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- A couple has a child with classical CAH. What is the probability of having a
child with classical CAH in the subsequent pregnancy?
The couple had a child with classical CAH and both parents are apparently
normal. This suggests that both parents are likely to be carriers. As CAH is an
autosomal recessive disorder, the probability of having a baby with classical
CAH in the subsequent pregnancy is one in four. Rarely, 1–2 % of patients with
CAH may have spontaneous mutations, which are not present in either of the
parents. Therefore, stimulated 17(OH)P and genotyping should be performed
in both parents to predict the outcome (Fig. 10.9 ).- A woman with classical CAH is planning pregnancy. What is the probability of
having a child with classical CAH?
Since the woman has classical CAH, she has severe mutation in both alleles of
the 21α-hydroxylase gene. If her partner is not harboring any mutations, then
all their children will be carriers and none of them will develop CAH. Hence,
the probability of having a child with classical CAH depends on the likelihood
of her partner being a carrier for a gene for classical CAH. The frequency of
carriers for classical CAH is 1 in 60 in general population, as disease fre-
quency is 1:16,000. The probability of having a child with classical CAH when
a woman has classical CAH and her partner is carrier for classical CAH is
50 % (one in two) as depicted in the fi gure given below. Therefore, the proba-
bility of having a child with classical CAH in the index patient is 1 in 120
(Fig. 10.10 ).Affected Child Carriers Normal- Normal
- Disease
Fig. 10.9 Inheritance
pattern of CAH in a
couple who are carriers
for the disease
10 Congenital Adrenal Hyperplasia