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- A woman with non - classical CAH is planning pregnancy. What is the probabil-
ity of having a child with classical CAH?
Non-classical CAH can be either due to the presence of severe and mild mutant
alleles or two mild mutant alleles of 21α-hydroxylase gene. If the woman has
non-classical CAH, the possibility of having a child with classical CAH arises
only if she has NCCAH due to severe and mild mutant allele and her partner is
a carrier for the gene for classical CAH. As approximately 75 % of patients with
non-classical CAH have one severe and mild mutant allele, the probability of
the index patient having one severe and mild mutant allele is three in four. The
frequency of carrier for classical CAH is 1 in 60 in general population. The
probability of having a child with classical CAH when a woman has non-clas-
sical CAH (with severe and mild mutant allele) and her partner is a carrier for
classical CAH is 25 % (one in four) as shown in the Fig. 10.12. Therefore, the
probability of having a child with classical CAH in the index patient is 1 in 320,
i.e., (3:4) × (1:60) × (1:4).Fig. 10.12 Inheritance pattern of CAH in a couple where mother has non-classical CAH (with
severe and mild mutant allele) and father is carrier for classical CAH
- Normal allele
- Mild mutant allele
- Severe mutant allele Classical Carrier Carrier Non-Classical
10 Congenital Adrenal Hyperplasia