A healthy couple, who recently emigrated from Eastern Europe, bring their 3-year-old son to the office for evaluation of an eczematous rash. On examination, the child also shows signs of intellectual disability and gait abnormality and has a musty body odor. What is the likelihood that this couple's next child will be affected with the same disease?

Question

A healthy couple, who recently emigrated from Eastern Europe, bring their 3-year-old son to the office for evaluation of an eczematous rash.  On examination, the child also shows signs of intellectual disability and gait abnormality and has a musty body odor.  What is the likelihood that this couple's next child will be affected with the same disease?

Quizplus · Accepted Answer

Intellectual disability, gait or posture abnormality, eczema, and a musty body odor are signs of phenylketonuria (PKU). PKU is an autosomal recessive disease caused by mutation of the gene that codes for phenylalanine hydroxylase. In the United States, phenylalanine levels are measured in all neonates to screen for PKU. Because PKU is inherited in an autosomal recessive fashion, both of the healthy parents must be heterozygous carriers of the mutation. The probability that their next child will inherit the disease is: The probability that a child will inherit a mutant allele from each carrier parent is equal to p₁ x p₂ = 1/4, as these are independent events. Educational objective: Intellectual disability, gait or posture abnormality, eczema, and a musty body odor in a toddler are signs of phenylketonuria (PKU). Most infants with PKU are born to 2 heterozygous carrier parents. The probability that heterozygous carrier parents will transmit an autosomal recessive disease such as PKU to a child is 1/4.

A Healthy Couple, Who Recently Emigrated from Eastern Europe, Bring