Hereditary mixed polyposis syndrome

Hereditary mixed polyposis syndrome (HMPS) is a rare inherited condition characterized by the development of multiple types of polyps in the colon and rectum. Unlike other polyposis syndromes where a single polyp type predominates, individuals with HMPS develop a mixture of polyp types including hyperplastic polyps, atypical juvenile polyps, sessile serrated adenomas, and conventional adenomas (tubular, tubulovillous, or villous adenomas). This mixed histological presentation is a hallmark feature that distinguishes HMPS from other hereditary polyposis conditions such as familial adenomatous polyposis or juvenile polyposis syndrome. The condition primarily affects the gastrointestinal system, specifically the large bowel. Polyps typically develop during adulthood and can number from a few to several dozen. A major concern with HMPS is the significantly increased risk of colorectal cancer if the condition is left unmonitored or untreated. The syndrome has been linked to genetic alterations in the region of chromosome 10q23 and, in some families, to duplications involving the GREM1 gene (also known as the SCG2 locus on chromosome 15q13.3), which encodes a BMP antagonist. Duplication upstream of GREM1 leads to ectopic expression of this gene in colonic epithelium, disrupting normal BMP signaling and promoting polyp formation. There is currently no cure for HMPS, and management focuses on regular colonoscopic surveillance to detect and remove polyps before they progress to malignancy. The frequency and timing of surveillance colonoscopies are individualized based on polyp burden and family history. In cases where polyps are too numerous to manage endoscopically, or if cancer develops, surgical intervention such as colectomy may be necessary. Genetic counseling is recommended for affected individuals and their at-risk family members to facilitate early detection and appropriate screening strategies.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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