An ancestral Ashkenazi haplotype at the HMPS/CRAC1 locus on 15q13-q14 is associated with hereditary mixed polyposis syndrome.

The putative locus for hereditary mixed polyposis syndrome (HMPS) in a large family of Ashkenazi descent (SM96) was previously reported to map to chromosome sub-bands 6q16-q21. However, new clinical data, together with molecular data from additional family members, have shown 6q linkage to be incorrect. A high-density genomewide screen for the HMPS gene was therefore performed on SM96, using stringent criteria for assignment of affection status to minimize phenocopy rates. Significant evidence of linkage was found only on a region on chromosome 15q13-q14. Since this region encompassed CRAC1, a locus involved in inherited susceptibility to colorectal adenomas and carcinomas in another Ashkenazi family (SM1311), we determined whether HMPS and CRAC1 might be the same. We found that affected individuals from both families shared a haplotype between D15S1031 and D15S118; the haplotype was rare in the general Ashkenazi population. A third informative family, SM2952, showed linkage of disease to HMPS/CRAC1 and shared the putative ancestral haplotype, as did a further two families, SMU and RF. Although there are probably multiple causes of the multiple colorectal adenoma and cancer phenotype in Ashkenazim, an important one is the HMPS/CRAC1 locus on 15q13-q14.

Clinical and molecular features of the hereditary mixed polyposis syndrome.

BACKGROUND & AIMS: Various inherited syndromes predispose to the development of colonic juvenile polyps and colorectal cancer, with potential importance for sporadic tumorigenesis. This study describes features of a possibly new syndrome of atypical juvenile polyps and other colonic tumors and compares these features with those of known gastrointestinal tumor syndromes. METHODS: A large family, St. Mark's family 96, with a tendency to develop colonic polyps of mixed histological types is described. Genetic linkage to known polyposis syndromes has been tested. RESULTS: Adenomatous and hyperplastic polyps occur in affected members of the family, although the characteristic lesion is an atypical juvenile polyp. Some affected individuals have developed polyps of more than one type, and individual polyps may contain features of more than one histological type. Polyps can undergo malignant change. Typically, fewer than 15 polyps are found at colonoscopy and there is no extracolonic disease associated with the development of polyps. The family's polyps seem to be inherited in an autosomal-dominant fashion, but the disease is probably unlinked to candidate loci with importance in colorectal tumorigenesis, such as APC, hMSH2, and hMLH1. CONCLUSIONS: We term this family's disease hereditary mixed polyposis syndrome (HMPS). Although mutations in the putative HMPS gene may be responsible for syndromes such as juvenile and Peutz-Jeghers polyposes, HMPS may also be a distinct disease.

Genetic mapping of hereditary mixed polyposis syndrome to chromosome 6q.

Hereditary mixed polyposis syndrome (HMPS) is characterized by atypical juvenile polyps, colonic adenomas, and colorectal carcinomas. HMPS appears to be inherited in an autosomal dominant manner. Genetic linkage analysis has been performed on a large family with HMPS. Data did not support linkage to the APC locus or to any of the loci for hereditary nonpolyposis colorectal cancer. Evidence that the HMPS locus lies on chromosome 6q was, however, provided by significant two-point LOD scores for linkage between HMPS and the D6S283 locus. Analysis of recombinants and multipoint linkage analysis suggested that the HMPS locus lies in a 4-cM interval containing the D6S283 locus and flanked by markers D6S468 and D6S301.