Hereditary Mixed Polyposis Syndrome

Definition

Hereditary syndrome characterized by the appearance of various types of polyps, many of which are mixed in pattern

Individuals and families may have mixtures of types of polyps and polyps containing mixed patterns
- Adenomas are most frequent type
  - Both tubular and villous
- Many polyps have features of juvenile polyps
  - Prominent edematous stroma
  - Cystic dilation of glands
  - Frequently resemble the polyps of Juvenile Polyposis syndrome
- Epithelium frequently serrated
  - May be mixed with other patterns
  - Classic hyperplastic polyps may be seen
    - Not clear if increased over normal
- Mixtures of above patterns are common
Polyps confined to colon and rectum
- Most cases have 1-15 polyps at presentation
  - Rarely over 50
Mean age at presentation 41 years
Increased incidence of colorectal adenocarcinoma
- Mean age 48, range 32-74
No familial extra-colorectal disorders reported
Autosomal dominant inheritance
- Genetic lesion not entirely resolved
  - BMPR1A has been proposed (Cheah, O'Riordan)
  - CRAC1 15q13-q21 has been proposed (Jaegher)
- Few kindreds reported
  - Most belong to one large Ashkenazi Jewish kindred

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting / updates: 12/27/09, 12/28/09 11/27/11