Related Experiment Video
Updated: Sep 27, 2025
Visualizing the Interrenal Steroidogenic Tissue and Its Vascular Microenvironment in Zebrafish
Published on: December 21, 2016
Molecular Diagnosis of Steroid 21-Hydroxylase Deficiency: A Practical Approach
María Arriba1,2, Begoña Ezquieta1,2
1Molecular Diagnostics Laboratory, Department of Laboratory Medicine, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
Insights
Genetic testing of the CYP21A2 gene is crucial for diagnosing congenital adrenal hyperplasia (CAH). This molecular analysis helps predict disease severity and guides genetic counseling for this common monogenic disorder.
Area of Science:
- Endocrinology and Genetics
- Molecular Diagnostics
Background:
- Congenital adrenal hyperplasia (CAH), primarily caused by steroid 21-hydroxylase deficiency (21-OHD) in 95% of cases, is a leading cause of adrenal insufficiency in children.
- The CYP21A2 gene encodes steroid 21-hydroxylase, and mutations in this gene are responsible for CAH.
Purpose of the Study:
- To highlight the critical role of CYP21A2 genotyping in diagnosing CAH.
- To emphasize the utility of molecular studies in predicting disease classification and aiding genetic counseling.
Main Methods:
- Detailed CYP21A2 genotyping is essential to accurately detect mutations, including pseudogene-gene chimeras and duplications.
- Analysis of a curated panel of known disease-causing alterations offers high diagnostic yield.
Main Results:
- CYP21A2 molecular alterations correlate strongly with the degree of enzymatic deficiency, enabling prediction and classification of clinical forms.
- Genetic testing provides reliable results, independent of physiological variations and analytical interferences.
Conclusions:
- CYP21A2 genetic testing is indispensable for identifying severe alleles in patients and carriers, including those with mild or late-onset forms.
- Molecular diagnosis of 21-OHD significantly improves disease management, genetic counseling, and applications like preimplantation diagnosis.
Abstract:
Adrenal insufficiency in paediatric patients is mostly due to congenital adrenal hyperplasia (CAH), a severe monogenic disease caused by steroid 21-hydroxylase deficiency (21-OHD, encoded by the CYP21A2 gene) in 95% of cases. CYP21A2 genotyping requires careful analyses that guaranty gene-specific PCR, accurate definition of pseudogene-gene chimeras, gene duplications and allele dropout avoidance. A small panel of well-established disease-causing alterations enables a high diagnostic yield in confirming/discarding the disorder not only in symptomatic patients but also in those asymptomatic with borderline/positive results of 17-hydroxyprogesterone. Unfortunately, the complexity of this locus makes it today reluctant to high throughput techniques of massive sequencing. The strong relationship existing between the molecular alterations and the degree of enzymatic deficiency has allowed genetic studies to demonstrate its usefulness in predicting/classifying the clinical form of the disease. Other aspects of interest regarding molecular studies include its independence of physiological variations and analytical interferences, its usefulness in the diagnosis of simple virilizing forms in males and its inherent contribution to the genetic counseling, an aspect of great importance taking into account the high carrier frequency of CAH in the general population. Genetic testing of CYP21A2 constitutes an irreplaceable tool to detect severe alleles not just in family members of classical forms but also in mild late-onset forms of the disease and couples. It is also helpful in areas such as assisted reproduction and preimplantation diagnosis. Molecular diagnosis of 21-OHD under expert knowledge definitely contributes to a better management of the disease in every step of the clinical course.
