The genetics of CAH
Matthew Neil Bainbridge / Associate Director - Pediatric Genomics
Rady's Children's Hospital
About 1 in 10,000 to 18,000 children are born with congenital adrenal hyperplasia (CAH). The most common cause of CAH, accounting for ~95% of all cases, is 21-hydroxylase deficiency (21HD). In the body 21-hydroxylase is created by a gene called CYP21A2. When this gene stops working properly not enough 21-hydroxylase is created. In south Asia, there are 6 main mutations in the CYP21A2 gene that cause CAH. These mutations may either make the gene work less efficiently or stop the gene from being made by the body at all. These latter mutations are more likely to lead to the more severe, salt wasting, form of the disease.
21HD is an autosomal recessive disease (see figure below). This means that both girls and boys have 2 copies of the gene and get the disease at approximately the same frequency. It also means you need to have both copies of this gene functioning improperly to get the disease. When you have one functioning copy and one non-functioning copy you will not have the disease but will be a “carrier” for CAH/21HD. In order to have a child with CAH, both parents must be carriers of the disease and the child must have gotten a bad copy of the gene from each parent. Most parents do not know they are carriers of the disease until they have a sick child as they show no outward signs of disease. Every child born to parental carriers has a 25% chance of getting the disease. If you have a child with CAH your other children will have a 50% chance of being a carrier for CAH and will be at increased risk of their own children developing CAH. Risk of having a child with CAH/21HD is increased if there is a family history of the disease, especially in families where cousins or other related individuals marry. Parents of a child with CAH should consider genetic testing for their unaffected children and should undergo genetic counselling to understand the risks of having more children.
Children fail to grow for a variety of reasons. Hormones, genetics, sleep, nutrition, general health and exercise are all factors for normal growth. If you suspect that your child is not growing normally, you are in the right place!
Congenital Adrenal Hyperplasia is an autosomal recessive genetic disorder, which means that it affects males and females in equal numbers, and that it requires both parents to pass on a gene in order for it to manifest as a disease. For a child to be born with any form of CAH, both parents must carry a gene for the disorder.
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We have created a Facebook page called Omkar's Journey with Congenital Adrenal Hyperplasia to chronicle all possible events and scenarios in the life of a child with CAH, with a view to let new parents know what to expect.
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The MAGIC Foundation India group on Facebook is a closed group and is for discussion and sharing of information to provide support services for the families of children afflicted with a wide variety of chronic and/or critical disorders, syndromes and diseases that affect a child's growth. This is a safe place for parents to exchange and seek information that might help them deal with the problem. Note that posts which are not relevant to disorders, syndromes and diseases that affect a child's growth and which are advertisements for sales of products, services or groups will be deleted and the person posting the message will be removed from the group without notice. If you wish to join this group: