A genetic counselor is consulted by a young man who is worried about developing Huntington's disease, an inherited disorder caus
ed by a dominant allele of a single gene. The young man explains that his cousin was recently diagnosed with Huntington's disease, and the news has caused him to consider his own risk of developing the disorder. Which of the following questions will best help the genetic counselor to evaluate the risk of the young man developing Huntington's disease and transmitting it to his children? (A) Were you and your cousin born in the same geographical area?
(B) Were your parents or grandparents ever diagnosed with Huntington's disease?
(C) Were you in physical contact with a person diagnosed with Huntington's disease?
(D) Were you ever exposed to substances that are suspected of causing Huntington's disease?
Answer: B - Were your parents or grandparents ever diagnosed with Huntington's disease?
Explanation: In autosomal dominant disorder, affected offsprings must have an affected parent. Unaffected parents do not transmit the disease.
Since the disease is caused by a dominant allele, the young man would only be at risk of having Huntington's disease if his parents or grandparents had ever been diagnosed with the disease. He needs not to worry if his parents or grandparents had never been diagnosed with the disease.
His cousin who has been diagnosed with the disease could have inherited the allele from his other parent.
