A 26-year-old woman comes to the office for follow-up. The patient and her husband want to have a child, and she inquires about the risk of certain genetic conditions, including cystic fibrosis (CF). The patient is from a small city with a stable Caucasian population, where the carrier frequency for CF is 1/30 Caucasian individuals. Her husband is from a nearby community, where CF carrier frequency in individuals of Asian descent is 1/100. Both the patient, who is Caucasian, and her husband, who is of Asian descent, are healthy. What is the probability that a child born to a mother from the Caucasian community and a father from the Asian community will have the disease?

Question

A 26-year-old woman comes to the office for follow-up.  The patient and her husband want to have a child, and she inquires about the risk of certain genetic conditions, including cystic fibrosis (CF).  The patient is from a small city with a stable Caucasian population, where the carrier frequency for CF is 1/30 Caucasian individuals.  Her husband is from a nearby community, where CF carrier frequency in individuals of Asian descent is 1/100.  Both the patient, who is Caucasian, and her husband, who is of Asian descent, are healthy.  What is the probability that a child born to a mother from the Caucasian community and a father from the Asian community will have the disease?

Quizplus · Accepted Answer

11ec160b_3769_bb88_9249_a57cc354baf1_MD0001_00 Cystic fibrosis (CF) is an autosomal recessive disease. The patient, who is Caucasian, has a 1/30 probability of carrying the mutant CFTR allele and her husband, who is of Asian descent, has a 1/100 probability of carrying the same allele. If a parent is a carrier, the probability that the child will inherit the mutant allele from that parent is 1/2. However, to develop CF, the child must independently inherit a mutant allele from each parent (1/2 x 1/2 = 1/4 probability). Therefore: P(affected child) = 1/4 x P(carrier mother) x P(carrier father) = 1/4 x 1/30 x 1/100 = 1/12,000. An equivalent solution would be to state that the probability that the mother is a carrier and will transmit the mutant allele is (1/30 x 1/2) and the probability that the father is a carrier and will transmit the mutant allele is (1/100 x 1/2). The probability that both events will occur, producing a child with CF, is the product of the probabilities of these independent events = (1/30 x 1/2) x (1/100 x 1/2) = 1/12,000. Educational objective: The probability that a child of parents from 2 populations with different mutant allele carrier frequencies will inherit an autosomal recessive disease is 25% multiplied by the carrier frequencies.

A 26-Year-Old Woman Comes to the Office for Follow-Up