A novel splice-site variant of the base excision repair gene MYH is associated with production of an aberrant mRNA transcript encoding a truncated MYH protein not localized in the nucleus

The MYH gene encodes a DNA glycosylase involved in the excision repair of adenines paired with 8-hydroxyguanines, a major component of oxidative DNA damage, and bi-allelic germline MYH mutations have been reported to predispose individuals to multiple colorectal adenomas and carcinoma. To determine whether the MYH gene is involved in gastric carcinogenesis, we examined blood specimens from 20 Japanese familial gastric cancer (GC) patients for MYH mutations by polymerase chain reaction–single-strand conformation polymorphism (PCR–SSCP) analysis followed by direct sequencing. Bi-allelic germline MYH mutations were not found in any of the specimens, but in addition to four known variants, a novel splice-site variant, IVS10-2A > G (c.892-2A > G), was found in two patients as its heterozygote. Reverse transcription–PCR analysis revealed that the IVS10-2A > G variant caused the production of an aberrant mRNA transcript encoding a truncated MYH protein. Immunofluorescence analysis showed that the wild-type MYH protein, but not the variant-type, is localized in the nucleus. We then searched for the IVS10-2A > G variant in 128 digestive tract cancer patients by PCR with confronting two-pair primers, and eight cancers from six patients with the IVS10-2A/G genotype were identified. However, no other germline MYH mutations or inactivation of the remaining wild-type allele was detected. We next tested the presumed correlation of the IVS10-2G allele with GC risk in a case-control study of 148 GC cases and 292 controls, but no significant difference in the distribution of the IVS10-2A > G variant was found between the cases and controls. Interestingly, the homozygote for the IVS10-2G allele was found in one GC case, but not in any controls. These results suggested that the ability to repair 8-hydroxyguanine in nuclear DNA may differ among Japanese individuals due to the splicing abnormality based on the MYH IVS10-2A > G variant, and that the bi-allelic IVS10-2A > G variation may be responsible for the occurrence of GC.