A prospective study of the clinical, genetic, screening, and pathologic features of a family with hereditary mixed polyposis syndrome.

In 1997, hereditary mixed polyposis syndrome (HMPS) was described in an Ashkenazi pedigree having colorectal polyps with mixed histology and risk for colorectal cancer (CRC). The mutation is now localized to 15q13-14. Since 1980, compliant relatives of an HMPS family were seen annually, tested genetically, and had colonoscopy offered every 1 to 2 yr from age 20 yr. The Israeli pedigree has 37 members (17 clinically affected by CRC or polyps), and seven of 13 available relatives entered our screening program. The others, followed-up elsewhere, provided clinical information. Half of our screened group had rectal bleeding; others were asymptomatic. Colonoscopy, performed a mean of four times, identified polyps in all seven patients (mean age 28 yr). Polyps were removed and included juvenile adenomas, mixed juvenile adenomas, hyperplastic polyps, mixed hyperplastic adenomas, serrated adenomas, and tubular adenomas. None of our screened patients developed CRC or extracolonic neoplasia. Linkage analysis localized their mutation to 15q13-14. This high-penetrance founder mutation so far is described only in Ashkenazim. The CRC pathway seems to be through juvenile and hyperplastic polyps. Mutation identification will aid screening for and evaluation of HMPS prevalence in Jewish and non-Jewish populations. Meanwhile, a cancer pedigree and correct classification of polyps will identify HMPS families. They require early and frequent colonoscopy, polypectomy, and elective extensive colectomy when indicated.