Can Congenital Adrenal Hyperplasia Be Inherited? Carrier Risk

If you have congenital adrenal hyperplasia (CAH) caused by a specific gene variant, you will pass one of your variant genes to your biological children. However, whether your child is born with the condition depends mostly on your partner’s genetics ^[1].

CAH is a group of autosomal recessive conditions, meaning it requires two disease-causing genetic changes (called pathogenic variants)—one inherited from each parent—to be present in the same gene for a person to have the condition ^[1]. The most common form of CAH is 21-hydroxylase deficiency, caused by variants in the CYP21A2 gene ^[1]. If your partner does not carry a pathogenic variant in the exact same gene that causes your CAH, your children will be carriers (they will inherit one variant from you) but will usually not have the condition ^[1].

If your CAH is caused by CYP21A2 and your partner is confirmed to be a carrier of a variant in the same gene, there is a 50% chance with each pregnancy that your child will inherit two variants and have CAH ^[1]. If your partner also has CAH caused by the same gene, all of your children will inherit two variants ^[1]. Note that having two pathogenic variants does not always mean a child will have the severe “classic” form of CAH; the specific variants inherited help predict the severity, though they cannot perfectly forecast the exact symptoms ^[2].

Carrier Risk in the General Population

Many people are carriers of a CAH gene variant and do not know it, as carriers usually do not show symptoms of classic CAH ^[1]. The likelihood of your partner being a carrier depends on their ancestry and which specific variants are considered ^{[3] [4]}.

For example, the classic form of 21-hydroxylase deficiency is estimated to occur in roughly 1 in 15,000 to 20,000 births globally ^{[5] [6]}. However, the carrier frequency for milder, non-classic variants is much higher in certain populations. One study estimated that 15% of people of Ashkenazi Jewish descent and roughly 9.5% of the US Caucasian study population were carriers of a non-classic variant ^[4]. In some specific geographic or founder populations (communities originating from a small group of ancestors), the prevalence can be even higher ^[7]. Because these are only population averages, they do not replace the need for specialized genetic testing for your partner.

Genetic Counseling and Partner Testing

If you have CAH or know you are a carrier and are planning a family, medical guidelines recommend preconception genetic counseling and partner testing ^{[8] [9]}.

A genetic counselor is a specialized healthcare professional who can help you understand your risks based on your exact genetic variants and family history ^[10]. Before testing your partner, it is usually necessary to molecularly confirm your own specific genetic variants ^[11].

Testing for CYP21A2 is technically complex. The gene has a highly similar pseudogene (a piece of DNA that looks like the gene but does not function) located right next to it, which can cause false results in standard tests ^{[12] [13]}. Standard carrier screening panels might miss complex structural changes or deletions. It is important that your partner receives testing through a laboratory experienced with CAH that looks closely at the full CYP21A2 gene ^{[9] [12]}. It is also important to know that no test is perfect; a negative result significantly reduces the risk that your partner is a carrier, but it cannot completely eliminate the risk of rare or hard-to-detect variants ^[13].

Family Planning Options and Pregnancy Considerations

If testing reveals that your partner is a carrier, a genetic counselor can walk you through your family planning options. These may include:

• Natural conception with or without prenatal diagnosis.
• Prenatal diagnosis, such as chorionic villus sampling (CVS) or amniocentesis, to test the fetus during pregnancy ^{[9] [14]}. These are invasive procedures with some risks.
• In vitro fertilization (IVF) with PGT-M (preimplantation genetic testing for monogenic diseases), which screens embryos for the specific CAH variants present in your family before implantation ^{[9] [12]}. This requires knowing the exact familial variants and building a custom test.

Pregnancy with CAH: If you are the one with CAH, you must carefully manage your condition during pregnancy. Do not stop or change your glucocorticoid or mineralocorticoid replacement therapy without consulting your endocrinologist ^[8]. Pregnancy, severe morning sickness, and labor can cause physical stress that requires coordinated care between your endocrinologist and an obstetrician experienced in high-risk pregnancies to adjust your medication dosages and prevent an adrenal crisis ^[8].