Is Simple Virilizing CAH Hereditary? Family Risk Explained

Yes, simple virilizing congenital adrenal hyperplasia (CAH) is a hereditary condition ^[1]. If you have a confirmed diagnosis caused by pathogenic variants (mutations) in the CYP21A2 gene, your children will inherit at least one of these variants from you. However, your children’s risk of actually having CAH depends largely on the genetics of your reproductive partner ^[2].

Understanding Autosomal Recessive Inheritance

CAH is an autosomal recessive genetic condition ^[3]. We inherit two copies of every gene—one from our mother and one from our father. Simple virilizing CAH is most commonly caused by pathogenic variants in the CYP21A2 gene, which provides instructions for making the 21-hydroxylase enzyme ^[4].

For a person to develop CYP21A2-related CAH, they must inherit two pathogenic variants of the gene—one from each parent ^[2]. Because you have simple virilizing CAH, you have two pathogenic variants. You will pass one of these variants to every child you have.

Because your child receives one variant from you, their risk depends on the gene copy they inherit from your partner. The probabilities below apply to each individual pregnancy, assuming your own CYP21A2 diagnosis is established:

*A negative test greatly reduces, but does not completely eliminate, the chance that your partner is a carrier (known as residual risk).

Important Note on Severity: The clinical form of CAH (salt-wasting, simple virilizing, or nonclassic) depends on the specific combination of variants a child inherits ^[7]. If your child inherits CAH, their symptoms and severity might be different from your own ^[6].

Partner Carrier Testing and Genetic Counseling

Medical guidelines recommend preconception genetic counseling and reproductive-partner testing for people with 21-hydroxylase deficiency ^[8][9]. Close relatives may also be carriers and can discuss voluntary testing with a genetic counselor.

The CYP21A2 gene is notoriously difficult to analyze. The active gene is located very close to a highly similar, inactive “pseudogene” (CYP21A1P). This similarity can complicate testing ^[10]. Therefore, your partner’s testing must evaluate both gene sequences and larger structural changes (like deletions, duplications, or gene conversions) and be performed by a specialized laboratory experienced in CAH testing ^[11][5].

Even with comprehensive testing, a negative result greatly reduces but does not completely eliminate the risk, as some rare variants may remain undetected ^[10][5].

Exploring Your Options

It is highly recommended that you and your partner speak with a genetic counselor—ideally before trying to conceive, but also if you are already pregnant ^[9][2]. A genetic counselor can help you navigate:

• Your own genetics: Understanding your exact variants is required to interpret your child’s risk ^[12].
• Pre-pregnancy options: In-vitro fertilization (IVF) with preimplantation genetic testing (PGT-M) is an option to select embryos without CAH. However, this requires identifying your familial variants beforehand to build a custom test ^[9].
• Prenatal testing: If you are already pregnant, options like chorionic villus sampling (CVS) or amniocentesis can diagnose the fetus. These are invasive procedures with their own risks, and a genetic diagnosis does not perfectly predict clinical severity ^[9].
• Birth planning: Even if the prenatal diagnosis is uncertain, knowing the risk allows your medical team to plan for a prompt newborn evaluation, which is critical to preventing early salt-wasting crises ^[13].