Cystic fibrosis in an autosomal recessive disease in humans

Cystic fibrosis in an autosomal recessive disease in humans. Mr. and Mrs. Doe are both heterozygous for a low penetrance disease allele, CFTR Arg117His. The estimated penetrance of the disease is 10%. What is the likelihood that their first child will not be affected?

Solution

Ans:

Cystic fibrosis transmembrane conductance regulator-related disorders encompass a disease spectrum from focal male reproductive tract involvement in congenital absence of the vas deferens to multiorgan involvement in classic cystic fibrosis. The reproductive, gastrointestinal, and exocrine manifestations of cystic fibrosis transmembrane conductance regulator deficiency are correlated with CFTR genotype, whereas the respiratory manifestations that are the main cause of morbidity and mortality in cystic fibrosis are less predictable.

(CF is an autosomal recessive disease with an incidence of 1/2500; square root of 1/2500 is 1/50).

However for the above question Answer is 97.5% likely the first child will not get affected with cystic fibrosis. Since both parents are heterozygous for a low penetrance disease allele, None of their three children are affected and chance that she\'s a carrier is 0%. The estimated penetrance of the disease is 10% then 97.5% the first child will not get affected with disease.