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(American Journal of Pathology. 2001;159:1293-1300.)
© 2001 American Society for Investigative Pathology

Regular Articles

Comprehensive Analysis of SMAD4 Mutations and Protein Expression in Juvenile Polyposis

Evidence for a Distinct Genetic Pathway and Polyp Morphology in SMAD4 Mutation Carriers

Kelly L. Woodford-Richens^*, Andrew J. Rowan^*, Richard Poulsom, Stephen Bevan, Reijo Salovaara, Lauri A. Aaltonen, Richard S. Houlston, Nicholas A. Wright and Ian P. M. Tomlinson^*

From the Molecular and Population Genetics Laboratory^*
and the Histopathology Laboratory,
Imperial Cancer Research Fund, London, United Kingdom; the Section of Cancer Genetics,
Institute of Cancer Research, Sutton, Surrey, United Kingdom; and the Departments of Medical Genetics and Pathology,
Haartman Institute, University of Helsinki, Finland

Juvenile polyposis syndrome (JPS; OMIM 174900) is a rare disorder which is characterized by the presence of hamartomatous polyps throughout the gastrointestinal tract and an increased risk of gastrointestinal malignancy. Mutations of the SMAD4 gene on chromosome 18q21.1 have been shown to cause a subset of JPS cases, with estimates ranging from 20% to >50%. Characterization of the genes that cause the remainder of JPS cases relies on the certainty that SMAD4 is not the causative gene. We have undertaken a comprehensive analysis of germline SMAD4 mutations in a cohort of JPS patients to define the spectrum of mutations that cause JPS. We have analyzed a series of polyps from these patients for SMAD4 protein expression. We have also performed a blinded assessment of polyp material to look for morphological differences between polyps from patients with and without a germline SMAD4 mutation. The results indicate that almost all germline SMAD4 mutations are readily detectable by screening genomic DNA using polymerase chain reaction-based methods; SMAD4 can be excluded as the causative gene in the majority of our JPS cohort. Loss of SMAD4 expression occurs in most polyps from SMAD4 mutation carriers, even those with missense germline mutations. SMAD4 loss in polyps is, however, not a feature of cases that are not caused by SMAD4 mutations, indicating that these polyps develop along a SMAD4-independent pathway. The morphology of polyps from SMAD4 mutation carriers is subtly different from other JPS polyps, notably including a more prominent epithelial component in the former.

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