Congenital means ‘from birth’, so all everyone with CAH was born with the condition, even if they have late onset varieties which didn’t show symptoms until later in life.
Autosomal means the condition affects both sexes equally.
Recessive means that in order to inherit CAH, the genes inherited from both mother and father must be affected.
Everyone is made of millions of cells. All of these cells normally have 46 chromosomes, 23 from each parent. Chromosomes govern your genetic make-up – for example whether you have blue eyes, brown hair or conditions such as CAH. The chromosomes are made up of Deoxyribonucleic Acid, known as DNA for short.
DNA has thousands of segments, called genes. Genes contain instructions for each cell – how it should be constructed, how it should operate and how it should repair itself.
If any of these genes are damaged they won’t work properly – the genes will be ‘mutated’. There are four types of mutations; deletion (where part of the DNA on a gene is lost), addition (where extra DNA is added), point mutation (where DNA is altered), and recombination (where DNA is swapped among different genes).
The different forms of CAH are caused by mutations of different genes including CP21A2, CP17A1 and CP11B1.
CAH is an autosomal recessive condition which means that faulty genes must be passed on by both parents.
A child will inherit, and be affected by CAH if a pair of mutated genes are passed on to them (one from the mother, and one from the father). On the other hand, if only one mutated gene is passed on (from either parent), the child will be an unaffected carrier of CAH. Finally, if no affected genes are passed on from either parent, the child will be unaffected.
There are 6 cases to consider when looking at the chances of having children with CAH. The chances are the same for each child – so for example, a 25% (1 in 4) chance of having a child with CAH doesn’t mean that if you had 4 children, 1 would have CAH. It means that every time a child is conceived, there is a 25% chance of them having CAH. It’s like rolling a dice – the chances of scoring a 6 are the same each time, regardless of what you scored on the time before.
We’ll take a look at the six cases below:
Case 1: Both parents have CAH – It is certain that any children would have CAH.
Case 2: Both parents are carriers of a CAH gene -There is a 25% chance that a child would be unaffected, a 25% chance that a child would have CAH, and a 50% (1 in 2) chance that a child would be a carrier.
Case 3: One parent has CAH, the other is a carrier – There is a 50% chance that any child would be a carrier, and a 50% chance that any child would have CAH.
Case 4: One parent has CAH, the other unaffected – It is certain that any children would be carriers.
Case 5: One parent is a carrier, the other is unaffected. There is a 50% chance that any child would be unaffected, and a 50% chance that any child would be a carrier.
Case 6: Both parents are unaffected – It is certain that any children would be unaffected.