Question

Cathy is pregnant for the second time. Her first child Donald, has Cystic fibrosis (CF). Cathy has two brothers Charles and Colin and a sister Cindy. Charles is married to an unrelated woman, Carolyn, and has a 2-year- old daughter, Debbie. Cathy’s parents are Bob and Betty. Betty’s sister Barbara is the mother of Cathy’s husband, Calvin. There is no previous family history of Cystic fibrosis.

1. What is the pattern of transmission of Cystic Fibrosis?
2. What is the risk for Cystic Fibrosis for Cathy’s next child?
3. Which people in this pedigree are obligate heterozygotes?

Answer 1

When Cathy is pregnant for the second time and first child has cystic fibrosis, it is the responsibility of the nurse to check the pattern of transmission of Cystic Fibrosis, risk rxisted for next child and heterozygotes.

1) The pattern of cystic fibrosis is different in father and mother. The person will have mutation of both copies of CFTR gene. If one mutated copy of gene is transmitted from each parrent then they will be the carrier. If father and mother is just carrier then their first child will have cf and second and third child will be carriers and fourth child will not be affected. If mother has cystic fibrosis, then first and second child has cf and third and fourth children will be carriers.

2) In Cathy's case she will be the carrier of cystic fibrosis and father is a carrier, hence Donald has cystic fibrosis and second child also has the risk of getting cf.