Russell F. Jacoby

MLH3: a DNA mismatch repair gene associated with mammalian microsatellite instability.

DNA mismatch repair is important because of its role in maintaining genomic integrity and its association with hereditary non-polyposis colon cancer (HNPCC). To identify new human mismatch repair proteins, we probed nuclear extracts with the conserved carboxy-terminal MLH1 interaction domain. Here we describe the cloning and complete genomic sequence of MLH3, which encodes a new DNA mismatch repair protein that interacts with MLH1. MLH3 is more similar to mismatch repair proteins from yeast, plants, worms and bacteria than to any known mammalian protein, suggesting that its conserved sequence may confer unique functions in mice and humans. Cells in culture stably expressing a dominant-negative MLH3 protein exhibit microsatellite instability. Mlh3 is highly expressed in gastrointestinal epithelium and physically maps to the mouse complex trait locus colon cancer susceptibility I (Ccs1). Although we were unable to identify a mutation in the protein-coding region of Mlh3 in the susceptible mouse strain, colon tumours from congenic Ccs1 mice exhibit microsatellite instability. Functional redundancy among Mlh3, Pms1 and Pms2 may explain why neither Pms1 nor Pms2 mutant mice develop colon cancer, and why PMS1 and PMS2 mutations are only rarely found in HNPCC families.

A Juvenile Polyposis Tumor Suppressor Locus at 10q22 Is Deleted From Nonepithelial Cells in the Lamina Propria

BACKGROUND & AIMS Juvenile polyps are characterized by an abundant lamina propria that lacks smooth muscle and may contain cystically dilated glands, with epithelium that seems normal and is nondysplastic. Rarely, an autosomal dominant inheritance pattern occurs. The aim of this study was to test the hypothesis that the genetic defect in both sporadic juvenile polyps and hereditary juvenile polyposis involves loss of function for a tumor suppressor gene. METHODS Allelic losses were detected by comparing normal DNA with tumor DNA from a series of 47 juvenile polyps from 16 patients using polymerase chain reaction amplification of microsatellite markers and fluorescent in situ hybridization (FISH). RESULTS Somatic deletions at 10q22 were detected in 39 of 47 juvenile polyps (83%) from 16 unrelated patients with either hereditary or sporadic juvenile polyps, and the minimum overlap localized juvenile polyposis coli to the 3-cM interval D10S219-D10S1696. Fluorescent in situ hybridization shows that the cells affected by deletion mutation reside exclusively in the lamina propria, not in the epithelium. CONCLUSIONS The location of a novel tumor suppressor gene on chromosome 10 that is affected by deletion mutation in the majority of juvenile polyps was mapped. Unlike adenomas and carcinomas of the colonic epithelium, juvenile polyps originate in the lamina propria.

Genetic instability associated with adenoma to carcinoma progression in hereditary nonpolyposis colon cancer

BACKGROUND & AIMS Genetic instability related to defective DNA mismatch repair genes may be involved in the pathogenesis of carcinoma in hereditary nonpolyposis colon cancer (HNPCC). However, nonneoplastic tissues from patients inheriting defects in human MSH2 or human MLH1 do not show significant genetic instability. The aim of this study was to determine whether acquisition of genetic instability at the adenoma stage promotes malignant transformation by studying adenoma-carcinoma progression in HNPCC. METHODS Dinucleotide repeat loci were analyzed by polymerase chain reaction from microdissected adenoma and/or carcinoma stages from formalin-fixed paraffin-embedded HNPCC tumors. RESULTS Although genetic instability was observed at some loci in almost all cases, the proportion of microsatellite loci altered was significantly less (P < 0.01) in completely benign adenomas (24%) than in benign areas of adenomas with malignancy (54%). Molecular fingerprints indicated intratumor heterogeneity, with evolution of related subclones of neoplastic cells. However, in all cases of tumor progression, at least one subclone from the adenoma stage was closely related to the carcinoma. CONCLUSIONS Some genetic instability develops at the benign adenoma stage in most HNPCC tumors. Adenomas with a greater rate of genetic instability are more likely to progress to carcinoma. Topographic genotyping data provides evidence supporting the hypothesis of adenoma-carcinoma progression in HNPCC.

Del(10)(q22.3q24,1) associated with juvenile polyposis

Juvenile polyps are the most frequent gastrointestinal polyps with a malignant potential for which the genetic basis is unknown. Juvenile polyps, with a normal epithelium but hypertrophic lamina propria, are histologically quite distinct from adenomatous polyps which have dysplastic changes in epithelial nuclei. Furthermore, the adenomatous polyposis coli (APC) gene on Chr 5, mutated somatically in adenomatous polyps and mutated in the germline of patients with familial adenomatous polyposis, is not linked to hereditary juvenile polyposis. We provide the first report indicating that a tumor suppressor gene associated with juvenile polyposis may be located at 10q22.3q24.1. Cytogenetic studies of a patient with juvenile polyposis and multiple congenital abnormalities of the head, extremities, and abdomen revealed a de novo interstitial deletion of Chr 10 as the only defect, del(10)(10q22.3q24.1).

Diffuse nodular lymphoid hyperplasia of the colon: polyposis syndrome or normal variant?

Diffuse nodular lymphoid hyperplasia (DNLH) has long been recognized in the pediatric population and in adults with common variable immunodeficiency (CVID).1 More recently, an association with HIV has been described.2 Little is known about the prevalence, natural history, and clinical significance of DNLH in immunocompetent adults. DNLH is a rare lymphoproliferative disorder of unknown etiology. Typically, numerous polypoid nodules composed of hyperplastic benign lymphoid tissue are present in the small and/or large intestinal mucosa.3 Although often an incidental finding, presentation is variable and depends on the size and extent of the nodules, as well as the presence or absence of underlying immunodeficiency. Treatment is directed at associated conditions because the disorder itself generally requires no intervention. Though considered benign by most investigators, several case reports document an association with malignant intestinal lymphoma.3,4 When DNLH is found predominantly in the colon, it can mimic a variety of polyposis syndromes but does not have the high risk of malignancy of familial adenomatous polyposis (FAP).5 This underscores the importance of obtaining biopsy specimens for histopathologic diagnosis and the need for increased awareness of this poorly understood entity.

Neoplasia in ileal pouch mucosa after total proctocolectomy for juvenile polyposis : Report of a case

PURPOSE: Patients treated with restorative proctocolectomy for familial adenomatous polyposis or ulcerative colitis occasionally develop disease in the ileal pouch similar to that originally present in the colon. We investigated the possibility of analogous involvement in the ileal pouch of juvenile polyposis patients. METHODS: Endoscopic surveillance for neoplasia throughout the gastrointestinal tract was performed, with retrieval of all polypectomy specimens for histologic classification using the criteria of Morson. RESULTS: Multiple large juvenile polyps were found in the ileal pouch of one patient less than 10 years after restorative proctocolectomy for hereditary juvenile polyposis. The pouch was much more severely affected than the proximal ileum, small intestine, or stomach. Although most polyps had a completely benign histologic appearance, three had moderate to severe dysplasia. DISCUSSION: Mucosal changes induced by bacteria or stasis of luminal contents may promote manifestation in the ileal pouch of the disease phenotype usually more evident in the colon. Patients with severe or generalized juvenile polyposis should be considered for periodic endoscopic surveillance of the ileal pouch beginning several years after restorative proctocolectomy.