Chelsea, age 14, recently had a colectomy. Her colon was lined with thousands of polyps. Pathology reported that these polyps were adenomas and a diagnosis of familial adenomatous polyposis (FAP) was made. Her 35-year-old mother and 38-year-old father are reported to be healthy. In fact, her father boasts that he hasn't needed to see a doctor since he was an adolescent. He has 3 children from a previous marriage. His father (Chelsea's paternal grandfather) died of colon cancer when he was 45 years old. FAP is an autosomal dominant condition caused by a mutated gene (Adenomatous Polyposis Coli (APC) located on the long arm of chromosome 5. Virtually all persons who carry the mutated gene will eventually develop 100s to 1000s of adenomatous polyps in the colon and if the colon is not removed, one or more of the polyps will eventually evolve into cancer. Persons are typically asymptomatic until polyps become cancerous. The mean age for colon cancer in persons with the mutated gene is 40 years of age. Persons with a mutated APC gene can have other manifestations such as gastric polyps, duodenal polyps, desmoid tumors, lipomas, osteomas, congenital hypertrophy of the retinal pigment epithelium, medulloblastoma, and/or hepatoblastoma.
1. What, if any, concerns do you have about Chelsea and her family?
2. What additional information do you want to know about Chelsea's family? FAP?
3. Are Chelsea's older half siblings at risk for FAP? Explain your answer.
4. The facts that different people with the same APC gene mutation can manifest different symptoms and can be affected to a different degree mean that the phenotype is (Choose the best answer and explain why you chose the answer that you did):
a) Heterogeneic and codominant
b) A phenocopy and incompletely penetrant
c) Incompletely dominant and allelic
d) Pleiotropic and variably expressed
5. Does a colectomy correct the phenotype or the genotype?
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