21-hydroxylase deficient congenital adrenal hyperplasia

21-hydroxylase defiency (21-OHD) is one of a group of conditions called congenital adrenal hyperplasia (CAH). All forms of CAH affect the adrenal glands which are located on top of the kidneys and produce a variety of hormones that regulate many essential functions in the body. In people with CAH due to 21-OHD, the adrenal glands produce excess androgens, which are male sex hormones.

There are three types of 21-OHD that vary in severity, they include two classic forms, known as the salt-wasting and simple virilizing types, and the third is called the non-classic type. The salt-wasting form is the most severe and causes people affected by the condition to lose a lot of sodium in the urine which can be life-threatening. People born with the simple-virilizing form of 21-OHD do not experience salt-wasting; however females born with either classic type are usually born with genitals that do not look clearly female or male (called ambiguous genitalia).

Females with non-classic 21-OHD do not have ambiguous genitalia but may experience other hormonal impacts such as irregular periods. Some people with non-classic CAH due to 21-OHD may not experience any signs or symptoms of the condition.

Quick facts about 21-hydroxylase deficient congenital adrenal hyperplasia
Genes: CYP21A2
Inheritance: Autosomal Recessive
Alternative Names: congenital adrenal hyperplasia due to 21-hydroxylase deficiency
Relevant resources for 21-hydroxylase deficient congenital adrenal hyperplasia

A quick genetics rundown

As humans we have about 23,000 genes. These genes are like tiny instruction manuals that influence our health, growth and development. We inherit half of our genes from our biological mum and the other half from our biological dad. These genes are lined up on structures called chromosomes. Most of us have 23 pairs of chromosomes. The first 22 pairs are called autosomes and for the most part - these are the same among men and women. The 23rd pair determine our sex - two X chromosomes for a female and one X and one Y chromosome for males.

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How is 21-hydroxylase deficient congenital adrenal hyperplasia inherited?

21-hydroxylase deficient congenital adrenal hyperplasia is known as an autosomal recessive condition. For autosomal recessive conditions, if a person has a variation in one copy of their gene, they are a carrier. This means that they are healthy because they also have a working copy of the gene. But, they can still pass their non-working copy to their child.

If the other parent also happens to be a carrier of the same gene, there is a 25% (1 in 4) chance that they both pass this gene variation on to their child — and as such, have a child affected by the disease.

If both parents are carriers of 21-hydroxylase deficient congenital adrenal hyperplasia, there’s a one in four chance that their children could develop symptoms.
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What is carrier screening?

Carrier testing is like a checkup for your genes. It tests to see if you carry a gene variation that could cause a serious genetic disease in your child. Eugene offers an inclusive genetic carrier screening panel that includes 21-hydroxylase deficient congenital adrenal hyperplasia, but there's a total 301 conditions that can be tested.

Eugene’s carrier test is a clinical grade test that can be done from the comfort of your own home — it’s just a saliva test. You're also paired with a genetic counsellor who provides mindful support and guidance every step of the way.

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Should parents screen for 21-hydroxylase deficient congenital adrenal hyperplasia before or early in pregnancy?

The biggest benefit of screening for 21-hydroxylase deficient congenital adrenal hyperplasia is that it can help future parents understand their reproductive risk so they can be ready and empowered to make more informed decisions. If neither partner are carriers, it provides reassurance and peace of mind that the risk of having a child with a genetic disease is low.

Since 90% of children that have a recessive genetic disease like 21-hydroxylase deficient congenital adrenal hyperplasia had no previous family history of it, it often feels completely out of the blue for the parents. Getting screened is a way to know this risk in advance, which can help familes manage or even prevent the disease in the first place.

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