Microsatellite instability and mutation analysis among southern Italian patients with colorectal carcinoma: detection of different alterations accounting for MLH1 and MSH2 inactivation in familial cases.
BACKGROUND
Microsatellite instability (MSI) is due to defective DNA mismatch repair (MMR) and has been detected at various rates in colorectal carcinoma (CRC). The role of MSI in colorectal tumorigenesis was assessed further in this study by both microsatellite analysis of two CRC subsets [unselected patients (n = 215) and patients <50 years of age (n = 95)], and mutation screening of the two major MMR genes MLH1 and MSH2 among familial CRC cases.


METHODS
PCR-based microsatellite analysis was performed on paraffin-embedded tissues. In CRC families, MLH1/MSH2 mutation analysis and MLH1/MSH2 immunostaining were performed on germline DNA and MSI+ tumour tissues, respectively.


RESULTS
The MSI+ phenotype was detected in 75 (24%) patients, with higher incidence in early-onset or proximally located tumours. Among 220 patients investigated for family cancer history, MSI frequency was markedly higher in familial [18/27 (67%)] than in sporadic [32/193 (17%)] cases. Three MLH1 and six MSH2 germline mutations were identified in 14 out of 36 (39%) CRC families. Prevalence of MLH1/MSH2 mutations in CRC families was significantly increased by the presence of: (i) fulfilled Amsterdam criteria; (ii) four or more CRCs; or (iii) one or more endometrial cancer. While MSH2 was found mostly mutated, almost all [8/9 (89%)] familial MSI+ cases with loss of the MLH1 protein were negative for MLH1 germline mutations.


CONCLUSIONS
Both genetic (for MSH2) and gene-silencing (for MLH1) alterations seem to be involved in CRC pathogenesis.
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002277:Carcinoma / Q000235:genetics*; D002471:Cell Transformation, Neoplastic; D015179:Colorectal Neoplasms / Q000235:genetics*; D004249:DNA Damage; D004252:DNA Mutational Analysis; D004260:DNA Repair / Q000235:genetics*; D005260:Female; D018095:Germ-Line Mutation; D006801:Humans; D007558:Italy; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics*; D008875:Middle Aged; D016133:Polymerase Chain Reaction