ORIGINAL RESEARCH article

Front. Pharmacol., 19 September 2018

Sec. Pharmacogenetics and Pharmacogenomics

Volume 9 - 2018 | https://doi.org/10.3389/fphar.2018.01008

Development of an AmpliSeqTM Panel for Next-Generation Sequencing of a Set of Genetic Predictors of Persisting Pain

  • 1. Institute of Clinical Pharmacology, Goethe-University, Frankfurt, Germany

  • 2. Institute for Molecular Medicine Finland, HiLIFE, University of Helsinki, Helsinki, Finland

  • 3. Fraunhofer Institute for Molecular Biology and Applied Ecology – Project Group Translational Medicine and Pharmacology, Frankfurt, Germany

  • 4. Division of Pain Medicine, Department of Anesthesiology, Intensive Care and Pain Medicine, University of Helsinki and Helsinki University Hospital, Helsinki, Finland

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Abstract

Background: Many gene variants modulate the individual perception of pain and possibly also its persistence. The limited selection of single functional variants is increasingly being replaced by analyses of the full coding and regulatory sequences of pain-relevant genes accessible by means of next generation sequencing (NGS).

Methods: An NGS panel was created for a set of 77 human genes selected following different lines of evidence supporting their role in persisting pain. To address the role of these candidate genes, we established a sequencing assay based on a custom AmpliSeqTM panel to assess the exomic sequences in 72 subjects of Caucasian ethnicity. To identify the systems biology of the genes, the biological functions associated with these genes were assessed by means of a computational over-representation analysis.

Results: Sequencing generated a median of 2.85 ⋅ 106 reads per run with a mean depth close to 200 reads, mean read length of 205 called bases and an average chip loading of 71%. A total of 3,185 genetic variants were called. A computational functional genomics analysis indicated that the proposed NGS gene panel covers biological processes identified previously as characterizing the functional genomics of persisting pain.

Conclusion: Results of the NGS assay suggested that the produced nucleotide sequences are comparable to those earned with the classical Sanger sequencing technique. The assay is applicable for small to large-scale experimental setups to target the accessing of information about any nucleotide within the addressed genes in a study cohort.

Introduction

Persisting pain has been proposed to result from a gene environment interaction where nerve injuries or inflammatory processes act as triggers while the clinical symptoms develop only in a minority of subjects (Lee and Tracey, 2013). A role of the genetic background in pain is supported by evidence of many variants modulating the individual perception of pain and the development of its persistence (Diatchenko et al., 2005; Lötsch et al., 2009b; Mogil, 2012). Genetic variants have been reported to confer protection against pain such as the rs1799971 variant in the μ-opioid receptor gene (OPRM1) (Lötsch et al., 2006), or to increase the risk for persisting pain such as the rs12584920 variant of the 5-hydroxytryptamine receptor 2A gene (HTR2A) (Nicholl et al., 2011) or the rs734784 polymorphism in the voltage-gated potassium ion channel modifier, subfamily S member 1, gene (KCNS1) (Costigan et al., 2010). Nevertheless, the genetic background of persisting pain is still incompletely understood (Mogil, 2009; Lötsch and Geisslinger, 2010) and under intense discussion.

Until recently, research focused on the role of selected functional genetic variants as protective or risk factors of persisting pain. This has changed with the broader availability of next generation sequencing (NGS) (Metzker, 2010). To make use of these technical advancements, we developed a custom AmpliSeqTM library and sequencing assay for efficient detection of genetic variants possibly associated with persisting pain. We propose an assay of a set of 77 genes supported by evidence of an involvement in pain and its development toward persistence. The set size fully uses the technical specifications of the AmpliSeqTM gene sequencing library technique.

Materials and Methods

Selection of Genes Relevant for Persisting Pain

A set of candidate genes with shown or biologically plausible relevance to persisting pain was created by applying a combination of criteria, which provided three different genetic subsets. Subset 1 was chosen exclusively on the basis of computational functional genomics based on a recently published analysis of persisting pain regarded as displaying systemic features of learning and neuronal plasticity (Mansour et al., 2014). As discussed previously (Ultsch et al., 2016), the view of chronic pain as a dysregulation in biological processes of learning and neuronal plasticity (Alvarado et al., 2013) seems to be captured by the controlled vocabulary (Camon et al., 2004) of the Gene Ontology (GO) knowledge base by the GO terms “learning or memory” (GO:0007611)1 and “nervous system development” (GO:0007399)2. An intersection of the genes annotated to these GO terms with a set of 539 “pain genes” identified empirically as relevant to pain provided the first subset of 34 genes described in detail previously (Ultsch et al., 2016). Briefly, the intersecting set of so-called “pain genes” consists of a combination of (i) genes listed in the PainGenes database (Lacroix-Fralish et al., 2007)3, (ii) genes causally involved in human hereditary diseases associated with extreme pain phenotypes, (iii) genes found to be associated with chronic pain in at least three human studies, and (iv) genes coding for targets of novel analgesics under clinical development (Lötsch et al., 2013).

Subset 2 consisted of genes that were reported to carry variants modulating the risk or the phenotypic symptoms in at least two different clinical settings of persisting pain. They were obtained using (i) a PubMed database search for the string “(chronic OR persisting OR neuropathic OR back OR inflammatory OR musculoskeletal OR visceral OR widespread OR idiopathic OR fibromyalgia) AND pain AND (polymorphism OR variant) NOT review,” to which genes highlighted in overviews on pain genetics (e.g., Edwards, 2006) were added. The intersection of the queried genes with the set of 539 “pain genes” (see above) provided a subset of 13 genes (Table 1).

Table 1

Gene symbolNCBIGene descriptionReference
Subset #1
ADCY1107Adenylate cyclase 1Vadakkan et al., 2006
BDNF627Brain-derived neurotrophic factorObata and Noguchi, 2006
CDK51020Cyclin-dependent kinase 5Yang et al., 2014
CHRNB21141Cholinergic receptor, nicotinic, beta 2Dineley et al., 2015
CNR11268Cannabinoid receptor 1 (brain)Smith et al., 1998
DLG41742Disks, large homolog 4 (Drosophila)Florio et al., 2009
DRD11812Dopamine receptor D1Onojjighofia et al., 2014
DRD21813Dopamine receptor D2Onojjighofia et al., 2014
DRD31814Dopamine receptor D3Potvin et al., 2009
EGR11958Early growth response 1Ko et al., 2005
FOS2353Cellular oncogene FOSAbbadie et al., 1994
FYN2534Src family tyrosine kinaseLiu et al., 2014
GABRA52558GABA A receptor, alpha 5Bravo-Hernández et al., 2016
GALR28811Galanin receptor 2Hulse et al., 2012
GRIN12902Glutamate receptor, NMDA 1Petrenko et al., 2003
GRIN2A2903Glutamate receptor, NMDA 2APetrenko et al., 2003
GRIN2B2904Glutamate receptor, NMDA 2BPetrenko et al., 2003
GRM52915Glutamate receptor, metabotropic 5Walker et al., 2001
HRH311255Histamine receptor H3Huang et al., 2007
KIT3815Tyrosine kinase KITSun et al., 2009
NF14763Neurofibromin 1Wolters et al., 2015
NGF4803Nerve growth factorKumar and Mahal, 2012
NTF44909Neurotrophin 4Kumar and Mahal, 2012
NTRK14914Neurotrophic tyrosine kinase 1Kumar and Mahal, 2012
OXT5020Oxytocin prepropeptideGoodin et al., 2015
PLCB123236Phospholipase C, beta 1Shi T.-J.S. et al., 2008
PRKCG5582Protein kinase C, gammaSluka and Audette, 2006
PRNP5621Prion proteinGadotti and Zamponi, 2011
PTN5764PleiotrophinGramage and Herradon, 2010
PTPRZ15803Protein tyrosine phosphatase Z 1Ultsch et al., 2016
RELN5649ReelinBuchheit et al., 2012
S100B6285S100 calcium binding protein BZanette et al., 2014
SLC6A46532Serotonin transporterOffenbaecher et al., 1999
TH7054Tyrosine hydroxylaseBravo et al., 2014
Subset #2
ADRB2154Adrenoceptor beta 2Hocking et al., 2010
COMT1312Catechol-O-methyltransferaseFeng et al., 2013
ESR12099Extrogen Receptor 1Ribeiro-Dasilva et al., 2009
GCH12643GTP cyclohydrolase 1Tegeder et al., 2006
IL1B3553Interleukin 1BLoncar et al., 2013
IL43565Interleukin 4Sugaya et al., 2002
IL63569Interleukin 6Shoskes et al., 2002
IL103586Interleukin 10Stephens et al., 2014
P2RX75027Purinergic Receptor P2X7Sorge et al., 2012
SCN9A6335Sodium voltage-gated alpha subunit 9Reimann et al., 2010
SOD26648Superoxide dismutase 2Schwartz et al., 2009
TNF7124Tumor necrosis factorLeung and Cahill, 2010
TRPV17442Transient receptor potential cation channel, subfamily V, member 1Bourinet et al., 2014
Subset #3
ABHD1226090Abhydrolase domain containing 12Kim, 2015
ABHD16A7920Abhydrolase domain containing 16AKim, 2015
ABHD657406Abhydrolase domain containing 6Kim, 2015
CACNG210369Calcium voltage-gated channel auxiliary subunit gamma 2Nissenbaum et al., 2010
CSF11435Colony stimulating factor 1Thuault, 2016
DRD41815Dopamine receptor D4Buskila et al., 2004
FAAH2166Fatty acid amide hydrolaseJayamanne et al., 2006
FKBP52289Fk506 binding protein 5Fujii et al., 2014
GDNF2668Glial cell derived neurotrophic factorSah et al., 2005
GFRA12674GDNF family receptor alpha 1Yamamoto et al., 2003
GPR13229933G protein-coupled receptor 132Hohmann et al., 2017
HCN2610Hyperpolarization-activated cyclic nucleotide-gatedTsantoulas et al., 2016
HLA-DQB13119Major histocompatibility complex, class II, DQ beta 1Dominguez et al., 2013
HLA-DRB13123Major histocompatibility complex, class II, DR beta 1Dominguez et al., 2013
HTR1A33505-hydroxytryptamine (serotonin) receptor 1ALindstedt et al., 2012
HTR2A33565-hydroxytryptamine (serotonin) receptor 2ANicholl et al., 2011
IL1R27850Interleukin 1 receptor type 2Stephens et al., 2014
KCNS13787Potassium voltage-gated channel, modifier subfamily S, member 1Costigan et al., 2010
LTB4R1241Leukotriene b4 receptorZinn et al., 2017
LTB4R256413Leukotriene b4 receptor 2Zinn et al., 2017
OPRD14985Opioid receptor delta 1Law et al., 2013
OPRK14986Opioid receptor kappa 1Guerrero et al., 2010
OPRM14988Opioid receptor mu 1Lötsch and Geisslinger, 2005
RET5979RET receptor tyrosine kinaseSnider and McMahon, 1998
RUNX1861Runt related transcription factor 1Chen et al., 2006
TLR47099Toll like Receptor 4Hutchinson et al., 2010
TRPA18989Transient receptor potential cation channel, subfamily A, member 1Bourinet et al., 2014
TRPM879054Transient receptor potential cation channel, subfamily M, member 8Bourinet et al., 2014
TRPV459341Transient receptor potential cation channel, subfamily V, member 4Bourinet et al., 2014
TSPO706Translocator proteinLoggia et al., 2015

Genes included in the proposed NGS panel of persisting pain, combined from three subsets included on different bases.

Subset #1 comprises d = 34 genes that had resulted from a computational functional genomics analysis (Ultsch et al., 2016) pursuing the hypothesis that persisting pain displays systemic features of learning and neuronal plasticity (Mansour et al., 2014). Hence, from a set of genes identified empirically as relevant to pain and listed in the PainGenes database (http://www.jbldesign.com/jmogil/enter.html, Lacroix-Fralish et al., 2007), those were selected that are annotated to the Gene Ontology (Ashburner et al., 2000) terms “learning or memory” and “nervous system development.” The references are those found to provide evidence for an association with pain, except for PTPRZ1 that was a novel finding in (Ultsch et al., 2016). Subset #2 comprises d = 13 genes identified empirically as relevant to pain and listed in the PainGenes database (http://www.jbldesign.com/jmogil/enter.html, Lacroix-Fralish et al., 2007) and reported to carry variants that modulated the risk or the symptomatology in at least two different clinical settings of persisting paint. Subset #3 comprises d = 30 genes repeatedly shown during the last several years to play a role in the human genetics of persisting pain or recently reported as novel players.

Finally, subset 3 comprised genes that have consistently been included in human pain research projects over the last several years. One of them is the OPRM1 gene that codes for the human μ-opioid receptor and which has been shown to modulate the time course of persisting cancer pain by delaying the necessity of opioid treatment (Lötsch et al., 2010). However, further genes were added such as the GDNF gene coding for the glial cell derived neurotrophic factor, which has been shown to be involved in a glia-dependent mechanism of neuropathic pain (Wang et al., 2014) although no modulating human genetic variants have been reported so far. Following expert counseling within the EU-funded “glial-opioid interface in chronic pain, GLORIA” research consortium (Kringel and Lötsch, 2015)4, a subset of 30 genes (Table 1) was identified. Thus, the complete set as the union of the three subsets comprised 43 + 13 + 30 = 77 genes that are proposed to be included in an NGS panel of human persisting pain.

DNA Sample Origin

Due to the costs of assay development (for details, see second paragraph of the Discussion), the AmpliseqTM panel was established in a limited number of n = 72 DNA samples. This corresponds to the number of samples used in comparable recent studies for NGS assay establishment and validation (Bruera et al., 2018; De Luca et al., 2018; Mustafa et al., 2018; Shah et al., 2018). To further limit the project costs, the AmpliseqTM panel was established in a subset of samples originating from a clinical cohort of 1,000 women who had undergone breast cancer surgery (Kaunisto et al., 2013; Lötsch et al., 2018). The study followed the Declaration of Helsinki and was approved by the Coordinating Ethics Committee of the Helsinki University Hospital. Each participating subject had provided a written informed consent including genetic studies.

Specifically, for the presently reported method establishment, a subsample of 72 women (age 58.4 ± 8 years, mean ± standard deviation, weight 69.3 ± 11 kg), was drawn from the clinical subgroup not having developed persisting pain during the observation period. This was believed to come closer to a random sample than a mixture of patients with persisting and without persisting pain. This limitation of the sample selection has probably affected which and how many variants were identified. However, it is unlikely to have jeopardized the general applicability of the gene selection heuristics, assay establishment and validation, and of the functional analysis of the selected subset of genes.

DNA Template Preparation and Amplification

A multiplex PCR amplification strategy for the coding gene sequences was accomplished online (Ion AmpliseqTM Designer)5 to amplify the target region specified above (for primer sequences, see Supplementary Table 1) with 25 base pair exon padding. After a comparison of several primer design options, the design providing the maximum target sequence coverage was chosen. The ordered 1,953 amplicons covered approximately 97.5% of the target sequence (Supplementary Table 2). A total of 10 ng DNA per sample was used for the target enrichment by a multiplex PCR and each DNA pool was amplified with the Ion AmpliseqTM Library Kit in conjunction with the Ion AmpliseqTM “custom Primer Pool”-protocols according to the manufacturer’s procedures (Life Technologies, Darmstadt, Germany).

After each pool had undergone 18 PCR cycles, the PCR primers were removed with FuPa Reagent and the amplicons were ligated to the sequencing adaptors with short stretches of index sequences (barcodes) that enabled sample multiplexing for subsequent steps (Ion XpressTM Barcode Adapters Kit; Life Technologies). After purification with AMPure XP beads (Beckman Coulter, Krefeld, Germany), the barcoded libraries were quantified with a Qubit® 2.0 Fluorimeter (Life Technologies, Darmstadt, Germany) and normalized for DNA concentration to a final concentration of 20 pmol/l using the Ion Library EqualizerTM Kit (Life Technologies, Darmstadt, Germany). Equalized barcoded libraries from seven to eight samples at a time were pooled. To clonally amplify the library DNA onto the Ion Sphere Particles (ISPs; Life Technologies, Darmstadt, Germany), the library pool was subjected to emulsion PCR by using an Ion PGM HI-Q View Template Kit on an PGM OneTouch system (Life Technologies, Darmstadt, Germany) following the manufacturer’s protocol.

Sequencing

Enriched ISPs which carried many copies of the same DNA fragment were subjected to sequencing on an Ion 318 Chip to sequence pooled libraries with seven to eight samples. During this process, bases are inferred from light intensity signals, a process commonly referred to as base-calling (Ledergerber and Dessimoz, 2011). The number of combined libraries that can be accommodated in a single sequencing run depends on the size of the chip, the balance of barcoded library concentration, and the coverage required. The high-capacity 318 chip was chosen (instead of the low-capacity 314 or the medium-capacity 316 chip) to obtain a high sequencing depth of coverage for a genomic DNA library with >95% of bases at 30x. Sequencing was performed using the sequencing kit (Ion PGM Hi-Q Sequencing Kit; Life Technologies, Darmstadt, Germany) as per the manufacturer’s instructions with the 200 bp single-end run configuration. This kit contained the most advanced sequencing chemistry available to users of the Ion PGM System (Life Technologies, Darmstadt, Germany).

Data Analysis

Bioinformatics Generation of Sequence Information

The raw data (unmapped BAM-files) from the sequencing runs were processed using Torrent Suite Software (Version 5.2.2, Life Technologies, Darmstadt, Germany) to generate read alignments which were filtered by the software into mapped BAM-files using the reference genomic sequence (hg19) of target genes. Variant calling was performed with the Torrent Variant Caller Plugin using as key parameters: minimum allele frequency = 0.15, minimum quality = 10, minimum coverage = 20 and minimum coverage on either strand = 3.

The annotation of called variants was done using the Ion Reporter Software (Version 4.4; Life Technologies, Darmstadt, Germany) for the VCF files that contained the nucleotide reads and the GenomeBrowse® software (Version 2.0.4, Golden Helix, Bozeman, MT, United States) to map the sequences to the reference sequences GRCh37 hg19 (dated February 2009). The SNP and Variation Suite software (Version 8.4.4; Golden Helix, Bozeman, MT, United States) was used for the analysis of sequence quality, coverage and for variant identification.

Based on the observed allelic frequency, the expected number of homozygous and heterozygous carriers of the respective SNP (single nucleotide polymorphism) was calculated using the Hardy-Weinberg equation. Only variants within the Hardy-Weinberg equilibrium as assessed using Fisher’s exact test (Emigh, 1980) were retained. The SNP and Variation Suite software (Version 8.4.4; Golden Helix, Bozeman, MT, United States) was used for the analysis of sequence quality, coverage and for variant identification.

Assay Validation

Method validation was accomplished by means of Sanger sequencing (Sanger and Coulson, 1975; Sanger et al., 1977) in an independent external laboratory (Eurofins Genomics, Ebersberg, Germany). As performed previously with different AmpliSeqTM panels (Kringel et al., 2017) and other genotyping assays (Skarke et al., 2004, 2005), four DNA samples have been chosen randomly from an independent cohort of healthy subjects and sequenced with the current NGS panel. For the detected variant type, single nucleotide polymorphisms from five different genomic regions for which clinical associations have been reported (Table 2), i.e., rs324420 (FAAH), rs333970 (CSF1), rs4986790 (TLR4), rs4633 (COMT), and rs17151558 (RELN) were chosen for external sequencing. Amplification of the respective DNA segments was done using PCR primer pairs (forward, reverse) of (i) 5′-TTTCTTAAAAAGGCCAGCCTCCT-3′ and 5′-AATGACCCAAGATGCAGAGCA-3′ (ii) 5′-GCCTTCAACCCCGGGATGG-3′ and 5′-CTCCGATCCCTGGTGCTCCTC-3′ (iii) 5′-TTTATTGCACAGACTTGCGGGTTC-3′ and 5′-AGCCTTTTGAGAGATTTGAGTTTCA-3′ (iv) 5′-CCTTATCGGCTGGAACGAGTT-3′ and 5′-GTAAGGGCTTTGATGCCTGGT-3′ (v) 5′-GTTATTCCTCTGTAAGCAGCTGCCT-3′ and 5′-TGTTTGTTTTAGATTGTGGTGGGTT-3′. Results of Sanger sequencing were aligned with the genomic sequence and analyzed using Chromas Lite® (Version 2.1.1, Technelysium Pty Ltd, South Brisbane, QLD, Australia) and the GenomeBrowse® (Version 2.0.4, Golden Helix, Bozeman, MT, United States) was used to compare the sequences obtained with NGS or Sanger techniques.

Table 2

GeneVariantdbSNP# accession numberKnown clinical associationReference
Pain context
FAAH1:46870761-SNVrs324420Effect of endocannabinoid degradation on painCajanus et al., 2016
FAAH1:46870761-SNVrs324420Cold and heat pain sensitivityKim et al., 2006b
CSF11:110466338-SNVrs333970Rheumatoid arthritisSolus et al., 2015
NGF1:115829313-SNVrs6330Procedural painErsig et al., 2017
NGF1:115829313-SNVrs6330Susceptibility to migraineCoskun et al., 2016
IL1B2:113590966-SNVrs1143634Adverse effects in postoperative painSomogyi et al., 2016
IL1B2:113590966-SNVrs1143634Low back painFeng et al., 2016
SCN9A2:167099158-SNVrs6746030Pain susceptibility in Parkinson diseaseGreenbaum et al., 2012
SCN9A2:167099158-SNVrs6746030Congenital insensitivity to painKlein et al., 2013
SCN9A2:167099158-SNVrs6746030Basal Pain SensitivityDuan et al., 2015
SCN9A2:167145122-SNVrs188798505Altered pain perceptionReimann et al., 2010
DRD33:113890815-SNVrs6280Acute pain in sickle cell diseaseJhun et al., 2014
DRD33:113890815-SNVrs6280Higher prevalence of migraineHu et al., 2014
ADRB25:148206646-SNVrs1042717Musculoskeletal painDiatchenko et al., 2006
ADRB25:148206885-SNVrs1800888MigraineSchurks et al., 2009
ESR16:152129077-SNVrs2077647MigraineSchürks et al., 2010
ESR16:152129077-SNVrs2077647Musculoskeletal painWise et al., 2009
OPRM16:154360797-SNVrs1799971Pain of various originsLötsch et al., 2009c
SOD26:160113872-SNVrs4880MigrainePalmirotta et al., 2015
IL67:22771039-SNVrs13306435Low back painEskola et al., 2010
OPRK18:54142157-SNVrs702764Neuropathic painGarassino et al., 2013
TLR49:120475302-SNVrs4986790Musculoskeletal painGbbbebura et al., 2017
TH11:2188238-SNVrs6357Widespread PainJhun et al., 2015
TH11:2190951-SNVrs6356MigraineCorominas et al., 2009
BDNF11:27679916-SNVrs6265Widespread PainErsig et al., 2017
DRD211:113283459-SNVrs6277Post-surgical painKim et al., 2006a
DRD211:113283477-SNVrs6275MigraineOnaya et al., 2013
P2RX712:121600253-SNVrs208294Cold pain sensitivityIde et al., 2014
P2RX712:121605355-SNVrs7958311Neuropathic painUrsu et al., 2014
HTR2A13:47409034-SNVrs6314Migraine susceptibilityYücel et al., 2016
TRPV117:3480447-SNVrs8065080Neuropathic painDoehring et al., 2011
KCNS120:43723627-SNVrs734784Neuropathic painDoehring et al., 2011
COMT22:19950235-SNVrs4633Postoperative painKhalil et al., 2017
COMT22:19950263-SNVrs6267Widespread PainLin et al., 2017
COMT22:19951271-SNVrs4680Altered pain perceptionWang et al., 2015
Other context
CSF11:110466466-SNVrs1058885PeriodontitisChen et al., 2014
CSF11:110466555-SNVrs2229165Carcinogenesis/breast cancerSavas et al., 2006
NTRK11:156846233-SNVrs6334NephropathyHahn et al., 2011
NTRK11:156848946-SNVrs6339Acute myeloid leukemiaSchweinhardt et al., 2008
SCN9A2:167143050-SNVrs41268673ErythromelalgiaKlein et al., 2013
TRPM82:234854550-SNVrs11562975Hyperresponsiveness in bronchial asthmaNaumov et al., 2015
TRPM82:234905078-SNVrs11563208Anthropometric parametersPotapova et al., 2014
DRD33:113890789-SNVrs3732783Phenotypic traits relevant to anorexia nervosaRoot et al., 2011
KIT4:55593464-SNVrs3822214Cancer riskPelletier and Weidhaas, 2010
KIT4:55602765-SNVrs3733542Glandular odontogenic cystSiqueira et al., 2017
HTR1A5:63257483-SNVrs1799921Bipolar disordersGoodyer et al., 2010
ADRB25:148206646-SNVrs1042717Cognitive dysfunction in opioid-treated patients with cancerKurita et al., 2016
DRD15:174868840-SNVrs155417Alcohol dependenceHack et al., 2011
HLA-DQB16:32629920-SNVrs41544112Ulcerative colitisAchkar et al., 2012
FKBP56:35544942-SNVrs34866878Clinical response in pediatric acute myeloid leukemiaMitra et al., 2011
CNR16:88853635-SNVrs1049353Bone mineral densityWoo et al., 2015
CNR16:88853635-SNVrs1049353Alcohol dependenceMarcos et al., 2012
CNR16:88853635-SNVrs1049353Nicotine dependenceChen et al., 2008
CNR16:88853635-SNVrs1049353ObesitySchleinitz et al., 2010
CNR16:88853635-SNVrs1049353Psychiatric disordersHillard et al., 2012
ESR16:152129077-SNVrs2077647Breast cancer susceptibilityLi et al., 2016
ESR16:152129077-SNVrs2077647Prostate cancer developmentJurečeková et al., 2015
ESR16:152129077-SNVrs2077647OsteoporosisSonoda et al., 2012
ESR16:152129308-SNVrs746432Mood disordersMill et al., 2008
ESR16:152201875-SNVrs4986934Endometrial cancer riskWedrén et al., 2008
OPRM16:154360508-SNVrs6912029Irritable bowel syndromeCamilleri et al., 2014
OPRM16:154360797-SNVrs1799971SchizophreniaSerý et al., 2010
OPRM16:154414573-SNVrs562859Depressive disorderGarriock et al., 2010
OPRM16:154414563-SNVrs675026Treatment response for opiate dependenceAl-Eitan et al., 2012
SOD26:160113872-SNVrs4880Development of type 2 diabetes mellitusLi et al., 2015
SOD26:160113872-SNVrs4880Breast cancer susceptibilityRodrigues et al., 2014
SOD26:160113872-SNVrs4880AsthmaYucesoy et al., 2012
ADCY17:45703971-SNVrs1042009Bipolar disorderShi J. et al., 2008
RELN7:103124207-SNVrs1062831Attention deficit hyperactivity disorderKwon et al., 2016
RELN7:103251161-SNVrs362691Childhood epilepsyDutta et al., 2011
OPRK18:54142154-SNVrs16918875Susceptibility to addictionKumar et al., 2012
TRPV18:72948588-SNVrs13280644Perception olfactory stimuliSchütz et al., 2014
TLR49:120475602-SNVrs4986791Breast cancer susceptibilityMilne et al., 2014
GRIN19:140051238-SNVrs6293SchizophreniaGeorgi et al., 2007
RET10:43610119-SNVrs1799939Hirschsprung’s diseaseVaclavikova et al., 2014
RET10:43615094-SNVrs1800862Medullary thyroid carcinomaCeolin et al., 2012
GFRA110:117884950-SNVrs2245020Age-related macular degenerationSchmidt et al., 2006
DRD411:637537-Delrs587776842Acousticous neurinomaNöthen et al., 1994
BDNF11:27720937-SNVrs66866077Irritable bowel syndrome-diarrheaCamilleri et al., 2014
DRD211:113283484-SNVrs1801028Neurologic disordersDoehring et al., 2009
GRIN2B12:13717508-SNVrs1806201Alzheimer’s diseaseAndreoli et al., 2014
TRPV412:110252547-SNVrs3742030HyponatremiaTian et al., 2009
P2RX712:121592689-SNVrs17525809Multiple sclerosisOyanguren-Desez et al., 2011
HTR2A13:47466622-SNVrs6305Susceptibility to substance abuseHerman and Balogh, 2012
LTB4R14:24785092-SNVrs34645221Asthma susceptibilityTulah et al., 2012
GABRA515:27182357-SNVrs140682Autism-spectrum disordersHogart et al., 2007
GRIN2A16:9943666-SNVrs2229193Hyperactivity disorderKim et al., 2017
DLG417:7099811-SNVrs17203281SchizophreniaTsai et al., 2007
SLC6A417:28530193-SNVrs6352Autism-spectrum disordersPrasad et al., 2009
NF117:29553485-SNVrs2285892NeurofibromatosisMaertens et al., 2007
HCN219:607984-SNVrs3752158Risk of depressionMcIntosh et al., 2012
PRKCG19:54394965-SNVrs3745396Osteosarcoma susceptibilityLu et al., 2015
PRNP20:4680251-SNVrs1799990Creutzfeldt-Jakob diseaseMead et al., 2009
HRH320:60791422-SNVrs3787430Risk of chronic heart failureHe et al., 2016
S100B21:48022230-SNVrs1051169SchizophreniaLiu et al., 2005

A list of coding human variants in the 77 putative chronic pain genes, found in the present random sample of 72 subjects of Caucasian ethnicity, for which clinical associations have been reported.

The selection is restricted to one or two publications per variant, and it focuses on a pain context corresponding to the main aim of the present NGS gene panel; however, functional variants highlighted in another clinical context are additionally provided in the lower part of the table. #Database of Single Nucleotide Polymorphisms (dbSNP). Bethesda (MD, United States): National Center for Biotechnology Information, National Library of Medicine. Available from: http://www.ncbi.nlm.nih.gov/SNP/ (Sherry et al., 2001).

Results

The NGS assay of the proposed set of 77 human genes relevant to persisting pain was established in 72 genomic DNA samples. As applied previously (Kringel et al., 2017), only exons including 25 bases of padding around all targeted coding regions for which the realized read-depths for each nucleotide was higher than 20 were contemplated as successfully analyzed. With this acceptance criterion the whole or almost whole coverage of the relevant sequences was obtained (Table 1; for details on missing variants, see Supplementary Table 3). The NGS sequencing process of the whole patient cohort required ten separate runs, each with samples of n = 7 or n = 8 patients. Coverage statistics were analogous between all runs and matched the scope of accepted quality levels [20–22]. A median of 2.85 ⋅ 106 reads per run was produced. The mean depth was close to 200 reads, the mean read length of called bases resulted in 205 bases and average chip loading was 71% (Figure 1A). To establish a sequencing output with a high density of ISPs on a sequencing chip, the chip loading value should exceed 60% (Life Technologies, Carlsbad, United States). The generated results of all NGS runs matched with the results obtained with Sanger sequencing of random samples (Figure 1B), meaning the accordance of nucleotide sequences between NGS and Sanger sequencing was 100% in all validated samples.

FIGURE 1

FIGURE 1

Assay establishment and validation. (A) Pseudo-color image of the Ion 318TM v2 Chip plate showing percent loading across the physical surface. This sequencing run had a 76% loading, which ensures a high Ion Sphere Particles (ISP) density. Every 318 chip contains 11 million wells and the color scale on the right side conduces as a loading indicator. Deep red coloration stays for a 100% loading, which means that every well in this area contains an ISP (templated and non-templated) whereas deep blue coloration implies that the wells in this area are empty. (B) Alignment of a segment of the ion torrent sequence of the COMT gene as a Golden Helix Genome Browse® readout versus the same sequence according to an externally predicted Sanger electropherogram. Highlighted is the COMT variant rs4633 (COMT c.186C>T → p.His62 =) as a heterozygous mutation and a non-mutated wild type. The SNP is part of the functional COMT haplotype comprising rs4633, rs4818 and rs4680, which showed >11-fold difference in expressed enzyme activity and was reported to be associated with different phenotypes of pain sensitivity (Diatchenko et al., 2005).

Following elimination of nucleotides agreeing with the standard human genome sequence GRCh37 g1k (dated February 2009), the result of the NGS consisted of a vector of nucleotide information about the d = 77 genes for each individual DNA sample (Figure 2). This vector had a length equaling the set union of the number of chromosomal positions in which a non-reference nucleotide had been found in any probe of the actual cohort. Specifically, a total of 3,185 genetic variants was found, of which 659 were located in coding parts of the genes, 1,241 were located in introns and 1,285 in the 3′-UTR, 5′-UTR, upstream or downstream regions. The coding variants for which a clinical or phenotypic association have been reported are listed in Table 2 together with an example of each variant. Most of the observed variants were single nucleotide polymorphisms (d = 571) whereas mixed polymorphisms (d = 26), nucleotide insertions (d = 18) or nucleotide deletions (d = 44) were more rarely found.

FIGURE 2

FIGURE 2

Mosaic plot representing a contingency table of the types of genetic variants detected by means of the present AmpliSeqTM panel versus the genes included in the assay. The vertical size of the cells is proportional to the number of variants of a particular type; the horizontal size of the cells is proportional to the number of variants found in the respective gene. The location of the variants is indicated at the left of the mosaic plot in letters colored similarly to the respective bars in the mosaic plot. Variants were not found at all possible locations of each gene, which causes the reduction of several bars to dashed lines drawn as placeholders and indicating that at the particular location no variant has been found in the respective gene. The figure has been created using the R software package (version 3.4.2 for Linux; http://CRAN.R-project.org/, R Development Core Team, 2008). UTR: untranslated region. NCExonic: Non-coding exonic.

Discussion

In this report, development and validation of a novel AmpliseqTM NGS assay for the coding regions and boundary parts of d = 77 genes qualifying as candidate modulators of persisting pain is described. The NGS assay produced nucleotide sequences that corresponded, with respect to the selected validation probes, to the results of classical Sanger sequencing. However, the NGS assay substantially reduced the laboratory effort to obtain the genetic information and provides the perquisites to be used in high throughput environments. In particular, the presented NGS assay is convenient for small up to large-scale setups. As mentioned in the methods section, a limitation of the present results applies to the identified genetic variants as only samples from Caucasian women were included. By contrast, the validity of gene selection and assay establishment is unlikely to be reduced by this selection chosen to remain within the financial limits of the present project.

Specifically, as observed previously (Kringel et al., 2017), the comprehensive genetic information and the high throughput are reflected in the assay costs. Specifically, sequencing of the 77 genes in 72 DNA samples required approximately € 18,000 for the AmpliSeqTM custom panel, € 5,500 for library preparation, € 700 for template preparation and € 700 for sequencing. Ten 318 sequencing chips cost around € 7,000 and in addition and basic consumables and laboratory supplies issued approximately € 800. With 7–8 barcoded samples loaded on ten chips, the expense to analyses the gene sequence for a single patient were around € 325. While NGS costs are likely to decrease in the near future (Lohmann and Klein, 2014), present assay establishment was therefore applied in DNA samples planned for future genotype versus phenotype association analysis, which required using DNA from patients of a pain-relevant cohort instead from a true random sample of healthy subjects.

As a result of the present assay development, a set of d = 77 genes was chosen as potentially relevant to persisting pain. The chosen set of genes differs from alternative proposals aiming at similar phenotypes (Mogil, 2012; Zorina-Lichtenwalter et al., 2016). However, when analyzing these alternatives for mutual agreement, only limited overlap could be observed (Figure 3). This emphasizes that the genetic architecture of persisting pain is incompletely understood, and several independent lines of research can be pursued. Of note, the present set showed the largest agreement with a set of d = 539 genes identified empirically as relevant to pain and listed in the PainGenes database (Lacroix-Fralish et al., 2007)6 or recognized as causing human hereditary diseases associated with extreme pain phenotypes (Lötsch et al., 2013; Ultsch et al., 2016). Combining all proposals into a large panel was not an option due to the technical limitations of the IonTorrent restricting the panel size to 500 kb (pipeline version 5.6.2); therefore, further genes would need to be addressed in separate panels.

FIGURE 3

FIGURE 3

Venn diagram (Venn, 1880) visualizing the intersections between the presently proposed set of human genes involved in modulating the risk or the clinical course of persisting pain (“Current set,” green frame), and two alternative proposals [“Mogil” (Mogil, 2012), blue frame and “Zorina-Lichtenwalter” (Zorina-Lichtenwalter et al., 2016), violet frame]. In addition, a set of d = 539 genes identified empirically as relevant to pain and either listed in the PainGenes database (http://www.jbldesign.com/jmogil/enter.html, Lacroix-Fralish et al., 2007) or added because recognized as causing human hereditary diseases associated with extreme pain phenotypes, found to be regulated in chronic pain in at least three studies including human association studies, or being targets of novel analgesics. The number of shared genes between data sets is numerically shown in the respective intersections of the Venn diagram. The figure has been created using the R software package (version 3.4.2 for Linux; http://CRAN.R-project.org/, R Development Core Team, 2008) with the particular package “Vennerable” (Swinton J., https://r-forge.r-project.org/R/?group_id=474).

In the present study sample, selected with a certain bias by using, as explained above for cost saving, clinical samples from only women and only Caucasians, a total of 659 genetic coding variants were found. Regardless of the sample preselection, 105 clinical associations (Table 2) could be queried for the observed variants from openly obtainable data sources comprising (i) the Online Mendelian Inheritance in Man (OMIM®) database7, (ii) the NCBI gene index database8, the GeneCards database9 [27] and the “1000 Genomes Browser”10 (all accessed in December 2017). The observation of functional variants in the present cohort preselected for the absence of pain persistence is plausible as (i) variants can exert protective effects against chronic pain and (ii) most genetic variants identified so far exert only small effects on pain and the individual result of their functional modulations depends on their combined effects or from the sum of positive and negative effects on pain perception (Lötsch et al., 2009a).

The selection of genes (Table 1) relied on empirical evidence of their involvement in pain. For subset #1 (d = 34), this had been shown for 33 genes in the original paper (Ultsch et al., 2016). As the hypothesis that persisting pain displays systemic features of learning and of neuronal plasticity (Mansour et al., 2014) could be substantiated at a computational functional genomics level, the further gene (PTPRZ1, protein tyrosine phosphatase Z 1) can also be regarded as supported by prior knowledge to be included in the present set. The subset comprised, for example, genes associated with the mesolimbic dopaminergic system, i.e., DRD1, DRD2, DRD3, which code for dopamine receptors, and TH, which is the coding gene for the tyrosine hydroxylase, a metabolic restricting enzyme in dopaminergic pathways, which have been implicated in promoting chronic back pain (Hagelberg et al., 2003, 2004; Jaaskelainen et al., 2014; Martikainen et al., 2015). Further 14 genes were involved in the circadian rhythm recognized as a modulatory factor in various pain conditions such as arthritis (Haus et al., 2012; Gibbs and Ray, 2013) and neuropathic pain (Gilron and Ghasemlou, 2014). The subset further included three NMDA receptor genes (GRIN1, GRIN2A, and GRIN2B) known to be major players in a number of essential physiological functions including neuroplasticity (Coyle and Tsai, 2004). In addition, metabotropic glutamate receptors (mGluR) have been implemented in several chronic pain conditions. One subtype, mGluR5, coded by GRM5, is of particular interest in the context of pain conditions as recent studies showed a pro-nociceptive role of mGluR5 in models of chronic pain (Walker et al., 2001; Crock et al., 2012). Furthermore, genes associated with histaminergic signaling such as HRH3 have been implicated in pain transmission (Hough and Rice, 2011) and analgesia (Huang et al., 2007).

The second subset of genes relied on a new PubMed search rather than on a previously published and hypothesis-based selection of candidate genes. A computational functional genomics analysis of this subset (details not shown) suggested its involvement in (i) immune processes and (ii) nitric oxide signaling. The genes annotated to the GO term “immune system process” included interleukin (IL1B, IL4, IL6, IL10) (Dinarello, 1994; Choi and Reiser, 1998; Mocellin et al., 2004; Nemeth et al., 2004) and histocompatibility complex related (HLA-B) genes (Dupont and Ceppellini, 1989), which have been shown to be involved in immunological mechanisms of pain (Sato et al., 2002; de Rooij et al., 2009). This is also supported by published evidence for the further genes in this list, such as, TNF (Vassalli, 1992; Franchimont et al., 1999), GCH1 (Schott et al., 1993) and P2RX7 (Chen and Brosnan, 2006). The second major process group emerging from the functional genomics analysis of the key evidence for genetic modulation of clinical chronic pain was nitric oxide signaling, in particular metabolic processes, summarized in this context under the GO term “reactive oxygen species metabolic process” which includes the genes IL6 (Deakin et al., 1995), TNF (Deakin et al., 1995; Katusic et al., 1998), ESR1 (Clapauch et al., 2014), IL10 (Cattaruzza et al., 2003), GCH1 (Katusic et al., 1998; Zhang et al., 2007), IL1B (Katusic et al., 1998), IL4 (Coccia et al., 2000), P2RX7 (Gendron et al., 2003), SOD2 (Fridovich, 1978). Furthermore, catecholamines including noradrenaline, adrenaline and dopamine have multiple functions in the brain and spinal cord including pain perception and processing (D’Mello and Dickenson, 2008). Catechol-O-methyltransferase, encoded by the COMT gene, is one of several enzymes that degrade dopamine, noradrenaline and adrenaline and has become one of the most frequently addressed genes in pain research (Nackley et al., 2006).

Finally, subset #3 (d = 30) consists of genes repeatedly shown to play a role in the genetic modulation of persisting pain in humans or, by contrast, included a few novel items only recently published in the context of pain. This included members of the transient receptor potential (TRP) family (TRPA1, TRPM8, TRPV4) that are expressed at nociceptors and which are well established players in the perception of pain via their excitation by chemical, thermal or mechanical stimuli (Clapham, 2003). This similarly applies to the opioidergic system represented by the inclusion of the genes coding for the major opioid receptors (OPRM1, OPRK1 OPRD1), which have been associated with variations in pain or opioid response in various settings (Lötsch and Geisslinger, 2005). The most important of this group, the μ-opioid receptor encoded by the OPRM1 gene, carriers several variants of which the 118 A>G (rs1799971) has been studied most extensively since the early description of its association with a functional phenotype in humans (Lötsch et al., 2002).

Almost half of the present sets of genes were chosen based on a computational functional genomics analysis that attributed persisting pain to GO processes of “learning or memory” and “nervous system development” (Ultsch et al., 2016) as likely to reflect systemic features of persisting pain. This implied a functional bias and therefore, the present set of d = 77 genes (Figure 4) was analyzed whether this bias prevailed when comparing it with the alternative sets of human genes proposed to modulate persisting pain (Mogil, 2012; Zorina-Lichtenwalter et al., 2016). As applied previously (Lippmann et al., 2018), the biological roles of the set of d = 77 genes were queried from the Gene Ontology knowledgebase (GO)11 (Ashburner et al., 2000) where the knowledge about the biological processes, the molecular functions and the cellular components of genes is formulated using a controlled and clearly defined vocabulary of GO terms. Particular biological roles of the set of d = 77 genes, among all human genes, were analyzed by means of over-representation analysis (ORA). This compared the occurrence of the particular GO terms associated with the present set of genes with their expected occurrence by chance (Backes et al., 2007). In contrast to enrichment analysis, any quantitative criteria such as gene expression values are disregarded (Backes et al., 2007). The analyses were performed using our R library “dbtORA” (Lippmann et al., 2018)12 on the R software environment (version 3.4.2 for Linux; R Development Core Team, 2008)13.

FIGURE 4

FIGURE 4

Top–down representation of the annotations (GO terms) representing the taxonomy of the functional differences between the set of d = 77 genes included in the proposed NGS panel of persisting pain and two alternative proposals of genes modulating persisting pain in humans (Mogil, 2012; Zorina-Lichtenwalter et al., 2016). The figure represents the results of an over-representation analysis of the present set of d = 77 genes against the reference comprising the set intersection of the alternative gene lists. A p-value threshold of 0.01 and Bonferroni α-correction were applied. Significant terms are shown as colored circles with the number of member genes, the number of expected genes by change and the significance of the deviation of the observed from the expected number of genes indicated (yellow = headline, red = significant term, blue = significant term located as a leave at the end of a taxonomy in the polyhierarchy). The graphical representation follows the standard of the GO knowledgebase, where GO terms are related to each other by “is-a,” “part-of,” and “regulates” relationships forming a polyhierarchy organized in a directed acyclic graph (DAG, Thulasiraman and Swamy, 1992). The figure has been created using our R library “dbtORA” (https://github.com/IME-TMP-FFM/dbtORA, Lippmann et al., 2018) on the R software package (version 3.4.2 for Linux; http://CRAN.R-project.org/, R Development Core Team, 2008) and the freely available graph visualization software GraphViz (http://www.graphviz.org, Gansner and North, 2000).

Surprisingly, the results of this analysis indicated that the functional bias of the present gene set toward “learning or memory” (GO:0007611) and “nervous system development” (GO:0007399) was not maintained against the alternative gene sets. Instead, a few more general GO terms such as “behavior” (“single organism behavior,” GO:0044708), or “response to organic cyclic compound” (GO:0014070) and response to alkaloid (GO:0043279), which could be identified as morphine and cocaine when repeating the analysis with a less conservative α-correction (further details not shown), were overrepresented, as well as the pain specific term “sensory perception of pain” (GO:0019233). A possible explanation that the selection bias of the present gene set was not maintained when comparing it with alternative proposals is that the two biological processes, “learning or memory” and “nervous system development,” reflect indeed an important biological function of persisting pain and even when choosing candidate genes without having these processes in mind as for the alternative gene sets, they are nevertheless included. This may be regarded as support for the present gene set as suitable candidates for future association studies with persisting pain phenotypes.

Although the present gene set has been assembled with a focus of a relevance to pain, many of its members have pharmacological implications. Specifically, 58 of the 77 genes (75%) have been chosen as targets of analgesics, approved or under current clinical development (Table 3). Moreover, several of the genes in the present NGS panel have been implicated in pharmacogenetic modulations of drug effects (Table 4). Possibly the most widely studied gene in analgesic research is OPRM1 because coding for the primary target of opioids (Peiro et al., 2016). Several polymorphisms have been described in OPRM1, among which the best characterized may be rs1799971 (OPRM1 118A>G) that leads to an asparagine to aspartate substitution at the extracellular terminal of the receptor protein (Bond et al., 1998). May studies have addressed this variant (for reviews, see Walter et al., 2013; Somogyi et al., 2015). Summarizing its effects, the variant is associated with decreased receptor expression and signaling efficiency (Oertel et al., 2012) which leads to reproducibly reduced pharmacodynamic effects in human experimental settings while the effect size seems insufficient to be a major factor of opioid response in clinical settings, despite several reports of modulations of opioid demands or side effects. For example, subjects carrying the 118A>G variant were found to have a reduced response to morphine treatment (Hwang et al., 2014), reduced analgesic response to alfentanil (Oertel et al., 2006) and demanded higher doses of morphine for pain relief (Klepstad et al., 2004; Hwang et al., 2014). However, the importance of this variant seems to be comparatively high in patients with an Asian ethnic background, which might be related to the higher allelic frequency as compared to other ethnicities. COMT is a key modulator of dopaminergic neurotransmission and in the signaling response to opioids The Val158Met polymorphism (rs4680) causes an amino acid substitution in the enzyme, which reduced the enzyme active to a forth (Peiro et al., 2016). Carriers of the homozygous Met/Met variant had lower morphine requirements than those with a the wild type COMT (Rakvag et al., 2005). Furthermore, a modulation of the effects of TRPV1 targeting analgesics is supported by observations that intronic TRPV1 variants were associated with insensitivity to capsaicin (Park et al., 2007) while the coding TRPV1 variant rs8065080 was associated with altered responses to experimentally induced pain(Kim et al., 2004). Moreover, gain-of-function mutations in TRPV1 have been associated with increased pain sensitivity (Boukalova et al., 2014), for which TRPV1 antagonists would enable a specific pharmacogenetics-based personalized cure.

Table 3

GeneStatusDrugActionCompany
ABHD12
ABHD16A
ABHD6PreclinicalBenzylpiperidin methanoneAcylamino-Acid-Releasing EnzymeScripps Research Institute
ADCY1Under Active DevelopmentNB-001Adenylate Cyclase InhibitorsForever Cheer International
ADRB2Phase II/IIIGencaroSignal Transduction ModulatorsARCA
BDNFPhase ICXB-909Nerve Growth Factor (NGF) EnhancersKrenitsky
CACNG2PreclinicalHanfangchinCalcium Channel BlockersMillenia Hope Kaken
CDK5Biological TestingLitvinolinCDK5/p25 InhibitorsHong Kong University
CHRNB2Biological TestingEpiboxidineNicotinic alpha4beta2 Receptor AgonistsPfizer
CNR1RegisteredEpidiolexCannabinoid Receptor AgonistsInSys Therapeutics
COMTClinicalNitecaponeCatechol-O-Methyl Transferase (COMT) InhibitorsOrion
CSF1
DLG4PreclinicalAB-125Protein InhibitorsLundbeck University of Copenhagen
DRD1Phase II/IIIEcopipamDopamine D1 Receptor (DRD1) AntagonistsMerck & Co.
DRD2Phase II/IIISarizotan hydrochlorideDopamine D2 Receptor (DRD2) AntagonistsNewron
DRD3Phase IIBrilaroxazineD3 Receptor (DRD3) AgonistsReviva Pharmaceuticals
DRD4Biological TestingMesulergine hydrochlorideDopamine Receptor AgonistsNovartis
EGR1Phase IIBrivoligideEGR1 Expression InhibitorsAdynxx
ESR1Phase IIZindoxifeneSelective Estrogen Receptor ModulatorsEvonik
FAAHPhase I/IIMinervalFatty Acid Amide Hydrolase (FAAH) InhibitorsScripps Research Institute
FKBP5Phase IIBarusibanOxytocin Receptor AntagonistFerring
FOSRegisteredMacrilenFOS Expression EnhancersStrongbridge Biopharma
FYNPhase IIBafetinibFyn Kinase InhibitorsNippon Shinyaku
GABRA5Phase IIIGanaxoloneGABA(A) Receptor ModulatorsMarinus Pharmaceuticals
GALR2PreclinicalNAX-810-2GAL2 Receptor LigandsNeuroAdjuvants
GCH1
GDNFPhase IIEdonerpic maleateSignal Transduction ModulatorsToyama
GFRA1
GPR132
GRIN1Phase IIDimiracetamSignal Transduction ModulatorsMetys Pharmaceuticals
GRIN2APhase IDexanabinolNMDA Receptor Antagonistse-Therapeutics Pharmos
GRIN2BPhase IGacyclidineNMDA Receptor AntagonistsINSERM
GRM5Phase IIMavoglurantSignal Transduction ModulatorsNovartis
HCN2ClinicalIvabradineAdrenoceptor AntagonistsServier
HLA-DQB1
HLA-DRB1
HRH3Phase IImmethridineHistaleanAbbott
HTR1APhase IIEltoprazine hydrochloride5-HT1A Receptor AgonistsElto Pharma
HTR2APhase IIMidomafetamine5-HT2 Receptor AgonistsAssoc
IL10Phase IIBT-063Signal Transduction Modulators Anti-IL-10Biotest AG
IL1BPhase IIIResunabIL-1beta InhibitorsCorbus
IL1R2
IL4
IL6PreclinicalAzintrelSignal Transduction Modulators Anti-IL-6Jazz Pharmaceuticals
KCNS1PreclinicalCrotamineVoltage-Gated K(V) Channel BlockersCeltic Biotech
KITPhase IIVatalanib succinateKIT (C-KIT) InhibitorsNovartis
LTB4RPhase IICoversinSignal Transduction ModulatorsAkari Therapeutics
LTB4R2Phase IICoversinSignal Transduction ModulatorsAkari Therapeutics
NF1
NGFPhase IIITanezumabAnti-Nerve Growth Factor (NGF)Pfizer
NTF4
NTRK1Phase IIDanusertibNTRK1 InhibitorsPfizer
OPRD1PreclinicalMetenkephalinDelta-Opioid Receptor AgonistsTNI Pharmaceuticals
OPRK1Phase IIIMorphine glucuronideOpioid Receptor AgonistsPAION
OPRM1RegisteredNaltrexonemu-Opioid Receptor AntagonistsPfizer
OXTPhase IIBarusibanOxytocin Receptor AntagonistFerring
P2RX7PreclinicalBIL-06vAnti-P2RX7Biosceptre International
PLCB1Biological TestingVinaxanthoneSignal Transduction ModulatorsRoche
PRKCGPhase IIIRydaptProtein Kinase C (PKC) InhibitorsYeda
PRNP
PTN
PTPRZ1
RELNPreclinicalIAIPsSerine Protease InhibitorsProThera Biologics
RETPhase IIDanusertibRet (RET) InhibitorsPfizer
RUNX1
S100B
SCN9APhase IIIPriralfinamideVoltage-Gated Sodium Channel BlockersNewron
SLC6A4Phase IILitoxetineSignal Transduction ModulatorsSanofi
SOD2Phase IIAvasopasem manganeseSuperoxide Dismutase (SOD) MimeticsMetaPhore
TH
TLR4Phase IIEritoran tetrasodiumToll-Like Receptor 4 (TLR4) AntagonistsEisai
TNFPhase IIIGivinostat hydrochlorideTNF-alpha Release InhibitorsItalfarmaco
TRPA1Phase IICannabidivarinTRPA1 AgonistsGW Pharmaceuticals
TRPM8Phase IICannabidivarinTRPM8 AntagonistsGW Pharmaceuticals
TRPV1Phase I/IIResiniferatoxinTRPV1 (Vanilloid VR1 Receptor) AgonistsIcos
TRPV4Phase IIGSK-2798745TRPV4 AntagonistsGlaxoSmithKline
TSPOClinical[11C]CB-184Translocator Protein (TSPO) LigandsTokyo Metrop Geriatr Hosp Inst Gerontol

Current targeting of the genes included in the proposed NGS panel of persisting pain by novel drugs that are currently under active clinical development and include analgesia as the main clinical target or at least as one of the intended clinical indication.

The information was queried from the Thomson Reuters Integrity database at https://integrity.thomson-pharma.com on July 11, 2018.

Table 4

Modulated processGeneVariantAffected drugFindingsReference
G protein coupled signalingCOMTrs4680 (Val158Met)MorphineCarriers of val/val and val/met genotype required higher morphine dose compared to carriers of met/met genotypeReyes-Gibby et al., 2007
DRD2rs6275HeroinePolymorphism is associated with decreased likelihood of headache disordersCargnin et al., 2014
DRD4rs1800955HeroinePolymorphism had lower pain threshold versus CC/CT controlsHo et al., 2008
OPRM1rs1799971 (A118G)Various opioidsTendency toward increased pain in dose-dependent manner with the μ-opioid receptor variant 118GLötsch et al., 2009c
OPRK1rs1051660MorphinePatients with the polymorphism and cancer-related pain may require a reduced dose escalation of morphineChatti et al., 2017
NeurotransmittersBDNFrs6265Various opioidsPolymorphism is associated with decreased likelihood of headache disordersCargnin et al., 2014
HTR2Ars12584920Various opioidsIncreased likelihood of having chronic widespread painNicholl et al., 2011
Ion ChannelsTRPV17 intronic SNPsCapsaicinTRPV1 polymorphisms had only 50% of the mRNA and protein expression levels of normally sensing subjectsPark et al., 2007
Proinflammatory CytokinesIL6rs1800795EtanerceptPolymorphism is associated with increased response to adalimumab, etanercept or infliximab in people with painful ArthritisDavila-Fajardo et al., 2014
OtherESR1rs2234693LeflunomidePolymorphism is associated with increased response to leflunomide in women with painful ArthritisDziedziejko et al., 2011
FAAHrs2295632Various opioidsPolymorphism is associated with increased risk of Respiratory InsufficiencyBiesiada et al., 2014
TLR4rs4986790MethotrexatePolymorphism associated with increased risk of adverse drug events when treated with folic acid and methotrexate in people with ArthritisKooloos et al., 2010
TNFrs361525InfliximabPolymorphism is associated with increased response to infliximab in people with painful ArthritisMaxwell et al., 2008

Summary of variants in genes included in the proposed NGS panel of persisting pain, that have been implicated in a pharmacogenetic context to modulate the effects of drugs administered for the treatment of pain or as disease modifying therapeutics in painful disease.

The information was derived by literature search and by querying the Pharmacogenetics Research Network/Knowledge base at http://www.pharmgkb.org (accessed in July 2018). Only key or example references are given.

Conclusion

The breakthrough in mapping the whole human genome (Lander et al., 2001; Venter et al., 2001) along with genome wide association studies (GWAS) has led to rapid advances in the knowledge of the genetic bases of human diseases (Wellcome Trust Case Control and Consortium, 2007). Genetic research in pain medicine has directed to the recognition of genes in which variants influence pain behavior, post-operative drug requirements, and the temporal developments of pain toward persistence (James, 2013). While many candidate gene association studies have identified multiple genes relevant for pain phenotypes (Fillingim et al., 2008), pain related genetic studies have so far been owned by investigations of a limited number of genes. Roughly ten genes or gene complexes account for over half of the extant findings and several of these candidate gene associations have held up in replication (Mogil, 2012). The selection of variants has been limited and they have been addressed in most studies repeatedly, leading to the perception that genetic research in pain produces often unsatisfactory results (Mogil, 2009). However, this may soon change with the arise of new technologies. In this manuscript, we present a validated NGS assay for a set of 77 genes supported by empirical evidence and computational functional genomics analyses as relevant factors modulating the risk for persisting pain or its clinical picture.

Statements

Author contributions

JL, DK, and EK conceived and designed the experiments. DK performed the experiments. JL and DK analyzed the data and wrote the paper. CL provided methodological expertise and bioinformatical tools. DK and JL interpreted the results. EK and MK provided DNA samples.

Funding

This work has been funded by the European Union Seventh Framework Programme (FP7/2007 – 2013) under grant agreement no. 602919 (“GLORIA”, EK and JL) and the LandesOffensive zur Entwicklung Wissenschaftlich-ökonomischer Exzellenz (LOEWE), LOEWE-Zentrum für Translationale Medizin und Pharmakologie (JL). These public funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fphar.2018.01008/full#supplementary-material

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Summary

Keywords

pain, data science, knowledge discovery, functional genomics, next generation sequencing (NGS)

Citation

Kringel D, Kaunisto MA, Lippmann C, Kalso E and Lötsch J (2018) Development of an AmpliSeqTM Panel for Next-Generation Sequencing of a Set of Genetic Predictors of Persisting Pain. Front. Pharmacol. 9:1008. doi: 10.3389/fphar.2018.01008

Received

24 May 2018

Accepted

17 August 2018

Published

19 September 2018

Volume

9 - 2018

Edited by

Ulrich M. Zanger, Dr. Margarete Fischer-Bosch-Institut für Klinische Pharmakologie (IKP), Germany

Reviewed by

Theodora Katsila, University of Patras, Greece; Cheryl D. Cropp, Samford University, United States

Updates

Copyright

*Correspondence: Jörn Lötsch,

This article was submitted to Pharmacogenetics and Pharmacogenomics, a section of the journal Frontiers in Pharmacology

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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