OBJECTIVETo analyze the mutational features of adenomatous polyposis coli (APC) gene and to explore the effect of mismatch repair (MMR) deficiency on its mutations in hereditary non-polyposis colorectal cancers (HNPCC).

METHODSPCR-based in vitro synthesized protein test (IVSP) assay and sequencing analysis were used to confirm somatic mutations of whole APC gene in 19 HNPCC patients.

RESULTSEleven cases with thirteen mutations were determined. The frequency of APC mutation was 58%(11/19). The exhibiting mutations consisted of 9 frameshift mutations and 4 nonsense ones, indicating the existence of more frameshift mutations (69%). All of frameshift mutations were deletion or insertion of 1-2 bp and most of them (7/9) happened at simple nucleotide repeat sequences, particularly within (A) n tracts (5/9). All of four nonsense mutations resulted from C to T transitions at CpG sites.

CONCLUSIONMutational inactivations of APC gene were detected in more than half of HNPCC patients in this study, indicating that APC mutation is a common molecular event in the tumorigenesis of HNPCC. According to the location of frameshift mutations at simple nucleotide repeat sequences and point mutations at CpG sites, it was suggested that endogenous mechanisms like MMR deficiency might exert an effect on the nature of APC mutations in most HNPCC.