Definition

The CYP21A2 gene encodes the 21-hydroxylase enzyme, which is involved in cortisol and aldosterone synthesis in the adrenal glands. Deficiency of this enzyme accounts for approximately 95% of congenital adrenal hyperplasia (CAH); precursors accumulate and the excess is redirected toward androgen synthesis. The classic form is divided into two subtypes: the salt-wasting form (which can lead to a life-threatening salt-wasting crisis in the newborn) and the simple virilizing form; the non-classic (late-onset) form has the mildest presentation.

Gene/region examined

CYP21A2 - Deletion/Duplication

Method

MLPA Analysis

Accepted sample types

EDTA blood, AF, CVS

Inheritance

Autosomal recessive; a pathogenic variant in both copies of the gene is required for the classic forms to occur, and carrier parents are usually asymptomatic. The classic form occurs in approximately 1 in 15,000 newborns and is included in newborn screening programs.

Related Tests

Inheritance Patterns

Describes how a genetic condition is passed on within a family. There are five main patterns

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Carrier (Heterozygous / Homozygous)

Why it matters: In autosomal recessive inheritance, when each parent is a carrier (while both appear healthy), the chance of their child being born with the disease is 25% in each

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VUS (Variant of Uncertain Significance)

This is the situation where the test has detected a change in the DNA, but the role of this change in the development of disease is unconfirmed.

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How to Read a Genetic Test Result (Positive / Negative / VUS)

A genetic test result falls into three main categories

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Types of Genetic Tests

A genetic test is a type of medical test that detects changes in genes, chromosomes or proteins. Today there are more than 77,000 genetic tests available.

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