Congenital adrenal hyperplasia (CAH) is a monogenic autosomal recessive disorder and more than 150 mutations of the CYP21A2 gene have been already reported and based on the degree of the enzymatic defect, CAH is classified into two major forms, classical (C) and non classical (NC). However, recent findings support the notion that rather than discrete phenotypic categories, CAH is better represented as a continuum of phenotypes, from severe to mild. The incidence of classic form of CAH ranges about 1:1.300 to 1:5.000, whereas in non-classic CAH is estimated from 1:500 to 1:100 births and the frequency of heterozygotes for CYP21A2 defects is considered quite common and varies considerably, ranging from 1:10 to 1:60. Accordingly, CAH constitutes one of the most frequent inborn errors of metabolism.

However, despite the high incidence and the monogenic nature of the disease there is a low genotype-phenotype correlation and several issues related to disorder remain unsolved. This phenomenon may be partly attributed to the fact that adrenal androgen hyper secretion is modified under stressful conditions and the final result depends on androgen’s receptor function on different tissues.

Especially in females where a mild increase in androgens may modify several aspects of body function the situations is further complicated. Indeed, the common clinical/hormonal findings of CAH patients with other common endocrinopathies (e.g polycystic ovary syndrome, subfertility) may delay the diagnosis leading to mismanagement and inappropriate treatment. Furthermore, we should keep in mind that the same patient display different requests through years and the caring physician should perform a tailor made approach in order to cover the special needs of the patient at different stages of life.

This long lasting disease demands the cooperation of both pediatric and adult endocrinologists as well as with other disciplines aiming to provide the best care to our patients. This series of articles will try to provide the reader with current knowledge on different aspects of CAH, with a special focus on reproduction, because several issues on clinical management have not fully clarified yet and the emergence of novel diagnostic and therapeutic approaches has not been fully implemented on everyday practice.

Keywords: Adrenals, 17OH progesterone, Cortisol, Fertility, Polycystic ovary syndrome

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