MUTATION SCREENING OF MSH2 AND MLH1 MESSENGER-RNA IN HEREDITARY NONPOLYPOSIS COLON-CANCER SYNDROME

Germline mutations in four human mismatch repair genes (MSH2, MLH1, PM S1, and PMS2) have been reported to cause hereditary non-polyposis col on cancer syndrome (HNPCC). The identification of germline mutations i n HNPCC kindreds allows precise diagnosis and accurate predictive test ing. To investigate further the genetic epidemiology of HNPCC and the nature and frequency of germline mutations in this disorder, we studie d 17 English HNPCC kindreds for germline mutations in MSH2 and MLH1. A previous genetic linkage study had suggested that most English HNPCC families will have mutations in one of these genes. Mutation analysis was performed in a three step process. (1) mRNA extracted from lymphob lastoid cell lines was analysed for gross rearrangements, (2) the in v itro transcription-translation (IVTT) assay was then performed to dete ct protein truncating mutations, and (3) partial cDNA sequencing of MS H2 or MLH1 was undertaken in families (n=6) linked to MSH2 or MLH1 but without a detectable mutation. Seven different germline mutations wer e identified in eight of 17 (47%) kindreds (five in MSH2 and three in MLH1). In three cases there was a deletion of a single exon in MSH2 mR NA, three mutations resulted in a truncated protein product, and two m issense mutations were identified by direct sequencing. Six mutations were novel. No precise correlation between genotype and phenotype was observed, although a MSH2 missense (Thr905Arg) mutation was associated with a susceptibility to multiple colorectal polyps. Age related risk s for colorectal and uterine cancer were similar for MSH2 and MLH1 mut ations.