A 38-year-old man is evaluated for bloody stools, weight loss, and anemia. The patient's medical history is unremarkable, and he does not take any medications. He smokes and consumes alcohol "socially." The patient's father died of colon cancer at the age of 40. His younger sister is afflicted with endometrial cancer. Examination reveals minimal right-sided abdominal tenderness without guarding against deep palpation. The stool tests positive for occult blood. A colonoscopy reveals a right-sided ulcerative colon mass. There are no polyps discovered. Adenocarcinoma is discovered after a mass biopsy.A mutation in which of the following genes is most likely responsible for this patient's condition?

Question

Quizplus · Accepted Answer

Eductional Objective: This case is typical of HNPCC, also known as Lynch syndrome, an autosomal dominant genetic predisposition to colon cancer. Colon cancer strikes HNPCC patients at a young age (age 50). In first-degree relatives, there is a high incidence of colon cancer and, on rare occasions, extraintestinal (eg, endometrial) cancers.
There is an inherited mutation in one of the genes responsible for DNA mismatch repair in HNPCC (eg, MSH2, MLH1). These genes' products proofread DNA during replication. Patients with HNPCC inherit a mutation in one allele, and the second allele is mutated later in life. Malignancies develop quickly when two dysfunctional copies are present.

A 38-Year-Old Man Is Evaluated for Bloody Stools, Weight Loss