Role of Inherited Defects of MYH in the Development of Sporadic Colorectal Cancer Takeshi Kambara, 1,2 Vicki L. J. Whitehall, 1 Kevin J. Spring, 1 Melissa A. Barker, 1 Sven Arnold, 1 Coral V. A. Wynter, 1 Nagahide Matsubara, 2 Noriaki Tanaka, 2 Joanne P. Young, 1 Barbara A. Leggett, 1* and Jeremy R. Jass 3* 1 Conjoint Gastroenterology Laboratory, Royal Brisbane and Women’s Hospital Research Foundation and Queensland Institute of Medical Research, Brisbane, Australia 2 Department of Gastroenterological Surgery, Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan 3 Department of Pathology, McGill University, Montreal, Quebec, Canada Biallelic germ-line variants of the 8-hydroxyguanine repair gene MYH have been associated with multiple colorectal adenomas that display somatic G:C3 T:A transversions in APC. However, the effect of single germ-line variants has not been widely studied. To examine the relationship between monoallelic MYH variants and susceptibility to sporadic colorectal cancer (CRC), 92 cases of sporadic CRC, 19 cases of familial CRC not meeting the Bethesda guidelines, 17 cases with multiple adenomas, and 53 normal blood donors were screened for 8 potentially pathogenic germ-line MYH variants. Loss of heterozygosity (LOH) at 1p adjacent to the MYH locus, microsatellite instability (MSI) status, and somatic mutations in KRAS2 and APC were analyzed in sporadic cancers. Neither homozygote nor compound heterozygote MYH variants were observed in the germ-line of any subjects with sporadic CRC. There was no difference in the incidence of monoallelic variants between this group (20 of 92, 22%) and cancer-free controls (14 of 53, 26%). However, the presence of monoallelic germ-line MYH variants was negatively associated with an MSI-high (MSI-H) tumor phenotype, with an incidence of only 1 of 23 (4%) MSI-H CRCs as contrasted with 19 of 69 (28%) non-MSI-H (P = 0.02). Further, 4 of 5 tumors with 1p LOH contained monoallelic MYH variants compared with 15 of 53 without 1p LOH (P = 0.04) and the normal population (P = 0.03). The presence of G:C3 T:A transversions in KRAS2 or APC was significantly more common in single MYH variant tumors (9 of 12) than in MYH wild-type tumors (11 of 33; P = 0.02). These results suggest that single germ-line variants of MYH may influence genetic pathways in CRC. © 2004 Wiley-Liss, Inc. INTRODUCTION Colorectal cancer (CRC) arises from the accumu- lation of multiple mutations in the oncogenes and tumor-suppressor genes (TSGs) that support nor- mal growth and differentiation in the colon (Fearon and Vogelstein, 1990). Defects in DNA repair lead to an increased frequency of mutations, thereby increasing the likelihood that cancer will develop (Jiricny and Marra, 2003). A deficiency in DNA mismatch repair is known to be the basis for he- reditary nonpolyposis colorectal cancer (HNPCC; Fishel et al., 1993; Leach et al., 1993; Bronner et al., 1994), and its associated tumor phenotype, high-level microsatellite instability (MSI-H), also has been demonstrated in approximately 15% of sporadic CRC cases (Aaltonen et al., 1993; Kinzler and Vogelstein, 1996). A subset of the remaining sporadic CRC cases has exhibited low-level MSI (MSI-L) in association with transcriptional silenc- ing of the DNA repair gene MGMT by promoter hypermethylation (Whitehall et al., 2001). Methyl- ation and silencing of MGMT have also been asso- ciated with G3 A transitions in KRAS2 and TP53 in CRC (Esteller et al., 2000, 2001). However, the mechanism underlying genetic instability in most sporadic non-MSI-H CRC is unknown. Recently, the human homologue of the base excision repair (BER) gene MutY (MYH) has been implicated in the causation of an adenoma-prone phenotype (Al- Tassan et al., 2002). MYH is a DNA glycosylase responsible for the removal from DNA of adenines mispaired with 8-hydroxyguanine (8-OG), one of the most mutagenic DNA products of oxidative DNA damage (Slupska et al., 1996; Hayashi et al., 2002). In a study by Parker et al. (2002), 33% of microsatellite stable (MSS) CRC cell lines ana- Supported by: in part, Royal Brisbane and Women’s Hospital Research Foundation; Australian National Health and Medical Re- search Council; U.S. National Institutes of Health; Grant number: UO1-CA74778; Walter Paulson Memorial Tumor Bank. *Correspondence to: Barbara A. Leggett or Jeremy R. Jass. E-mail: barbara_leggett@health.qld.gov.au E-mail: jeremy.jass@mcgill.ca Received 19 September 2003; Accepted 16 December 2003 DOI 10.1002/gcc.20011 Published online 26 February 2004 in Wiley InterScience (www.interscience.wiley.com). GENES, CHROMOSOMES & CANCER 40:1–9 (2004) RESEARCH ARTICLE © 2004 Wiley-Liss, Inc.