629 Hereditary non-polyposis colorectal cancer, first described in 1913, is char- acterized by early onset colorectal can- cer (mean age, 40 years). 1 HNPCC accounts for approximately 3% of all colorectal cancers and has an increased frequency of certain extracolonic neo- plasms. 2,3 The Amsterdam Criteria stipulate that HNPCC families should include 3 members with a diagnosis of colorectal cancer in 2 successive gen- erations, with one affected member who is a first-degree relative of the other two. 4 One affected member must have been given the diagnosis before age 50 years, and familial adenomatous polyposis must be ruled out. Subse- quent genetic analysis of some HNPCC families revealed linkage to chromosomes 2p and 3p, 5,6 now known to be the location of 2 of the DNA mismatch repair genes. 7,8 At least 5 human homologues of the yeast DNA MMR genes have been implicat- Germline characterization of early-aged onset of hereditary non-polyposis colorectal cancer Sherry C. Huang, MD, Joel E. Lavine, MD, PhD, Patricia S. Boland, BSN, PNP, Robert O. Newbury, MD, Richard Kolodner, PhD, Thu-Thao T. Pham, BS, Christian N. Arnold, MD, C. Richard Boland, MD, and John M. Carethers, MD From the Division of Gastroenterology and Nutrition, Department of Pediatrics, University of California, San Diego; Children’s Hospital and Health Center, San Diego, California; Division of Gastroenterology, Department of Medicine, and Cancer Center, University of California, San Diego; and Veteran’s Administration Research Service, San Diego, California. Supported in part by the American Digestive Health Foundation/American Gastroenterological Association/Astra Merck Fellowship/Faculty Transition Award (to S.C.H.), Public Health Ser- vice grants CA 39233 (to C.R.B.) and DK02433 (to J.M.C.), the Robert Wood Johnson Foun- dation (to J.M.C.), and the Charlotte Geyer Foundation (to J.M.C.). Submitted for publication June 16, 2000; revisions received Oct 3, 2000, and Nov 30, 2000; accepted Dec 4, 2000. Reprint requests: John M. Carethers, MD, VA San Diego Healthcare System, GI Section (9-111D), 3350 La Jolla Village Dr, San Diego, CA 92161. Copyright © 2001 by Mosby, Inc. 0022-3476/2001/$35.00 + 0 9/21/113620 doi:10.1067/mpd.2001.113620 hMLH1 Human mut L homolog gene hMSH2 and Human mut S homolog genes hMSH6 HNPCC Hereditary non-polyposis colorectal cancer hPMS1 and Human post meiotic segregation hPMS2 genes IVTT In vitro transcription translation assay MMR Mismatch repair MSI Microsatellite instability PCR Polymerase chain reaction TGFβRII Transforming growth factor-β type II receptor gene Objectives: Hereditary non-polyposis colorectal cancer (HNPCC) is char- acterized by the early onset of colorectal cancer (~40 years). Adolescent colorectal cancer is unusual in HNPCC families. We speculated that some DNA mismatch repair germline mutations might be associated with early onset of disease. Study design: Genomic DNA was extracted from members of a kindred with virulent HNPCC fitting the Amsterdam Criteria for HNPCC and se- quenced for 2 DNA mismatch repair genes, hMSH2 and hMLH1. A sigmoid adenocarcinoma from the 14-year-old proband was analyzed for high- frequency microsatellite instability and immunostained for DNA mismatch repair gene expression. Results: A germline mutation was identified at nucleotide 676 (codon 226) of the hMLH1 gene. The C to T transition created a nonsense mutation, truncating the hMLH1 protein. This mutation also alters the splice donor sequence, because nucleotide 676 is 2 base pairs from the 3´ end of the exon 8. The proband’s tumor demonstrated high-frequency microsatellite insta- bility and displayed loss of hMLH1 expression, indicating bi-allelic inactiva- tion of hMLH1. Conclusions: A complex mutation of hMLH1 at codon 226 is associated with adolescent onset of colorectal cancer in an HNPCC family. Genetic screening of other suspected HNPCC families with unusually young mem- bers with cancer might reveal certain genotypes with particularly virulent forms of this disease. (J Pediatr 2001;138:629-35) See related article, p 621. ORIGINAL ARTICLES