Current Aspects of Genetic Diagnosis of 21-Hydroxylase Insufficiency

Objective of the Review: To discuss the current peculiarities of 21-hydroxylase insufficiency diagnostics. Key Points. Congenital adrenal hyperplasia (CAH) is a group of autosomal-recessive pathologies, associated with a defective enzyme or transport protein participating in cortisol biosynthesis. Currently, there is information on CAH genetics including information on 21-hydroxylase insufficiency. Neonatal screening, antenatal and postnatal methods to diagnose 21-hydroxylase deficit have been developed. Timely diagnosis and correct therapy have been found to facilitate normal physical and mental development of patients. Molecular genetic testing for CAH associated with 21-hydroxylase deficit is widely used both in Russia and globally and is of importance for differential diagnosis, identification of pathogenic CYP21A2 gene carriers and adequate genetic counselling. The best strategy to diagnose 21-hydroxylase insufficiency is 2-stage CYP21A2 gene analysis. The test should include both gene sequence analysis and identification of point replacements, minor deletions and duplication (e.g., dideoxynucleotide chain-termination method or Next Generation Sequencing), and identification of extended deletions and duplication (multiplex ligation dependent probe amplification, real-time polymerase chain reaction). Such a comprehensive approach can help finding a majority of types of possible changes. Conclusion. Correct genetic testing methods ensure detection of pathogen variants in CYP21A2 gene; evaluation of the possible rate of clinical manifestations of the disease, both during antenatal testing and if an unknown clinical CAH form is encountered; prescribing an adequate therapy; and ensuring genetic counselling in order to develop a management strategy, including when planning for pregnancy in a woman with confirmed CAH. Keywords: congenital adrenal hyperplasia, CYP21A2 gene, genetic counselling, 21-hydroxylase