Question

A 15-year-old boy is referred to a genetics clinic to rule out neurofibromatosis 1. He reports having 25 café-au-lait spots and has started getting lumps and bumps on his skin since he hit puberty. During the family history, he describes his brother as being born with bowed legs and reports that he died at age 12 from a tumor in his neck that had been there since birth. He remembers that his brother had some birthmarks, but not nearly as many as he has. He does not recall his parents having any birthmarks, but they are not with him at the appointment.

What inheritance pattern for the disease is occurring in this family?
(A) autosomal dominant
(B) autosomal recessive
(C) X-lined dominant
(D) X-linked recessive
(E) multifactorial

Answer 1

The inheritance pattern for neurofibromatosis in the family is autosomal dominant, indicated by the presence of café-au-lait spots and skin tumors in the boy and the tumor in his deceased brother.

Step-by-step explanation:

The inheritance pattern for neurofibromatosis in the described family is autosomal dominant. This is evidenced by the presence of characteristic symptoms such as café-au-lait spots and skin tumors (lumps and bumps) in the 15-year-old boy and the previous history of a tumor in his deceased brother. Since autosomal dominant conditions only require one copy of the faulty gene to be present for the disorder to manifest, it is likely that one of the parents carries the defective gene, even if they do not exhibit symptoms. Neurofibromatosis type I is known to be an autosomal dominant condition where those heterozygous for the gene (Nn) have the condition, and those homozygous for the normal gene (nn) do not.