Mutational germline analysis of hMSH2 and hMLH1 genes in early onset colorectal cancer patients.

EDITOR—Hereditary non-polyposis colorectal cancer (HNPCC) is a heterogeneous autosomal dominant disease with incomplete penetrance. The frequency is estimated at 1:200/1:1000. HNPCC results from constitutional mutation in one of the five human mismatch repair genes (MMR) that have so far been implicated: hMSH2, hMLH1, hPMS1, hPMS2, and hMSH6. 2 hMSH2 and hMLH1 account for the majority of mutations found in HNPCC families (25-70%). The function of MMR genes is to maintain genetic stability and tumour DNA from HNPCC patients shows an accumulation of replication errors exhibiting an instability phenotype at microsatellite loci (MSI). 4 Standard criteria have been established to define HNPCC clinically. These are known as the “Amsterdam criteria” and require that at least two generations be aVected by colorectal cancer (CRC), that three or more relatives with histologically verified CRC be present, one of whom is a first degree relative of the other two, and at least one case of CRC be diagnosed before the age of 50. The syndrome is characterised by synchronous and metachronous CRC tumours and by association of certain types of extracolonic tumours, especially endometrial neoplasia. In 45-86% of cases, genetic testing characterises the mutation in the index patient for each HNPCC family identified and predicts a possible predisposition to colon and/or related syndrome cancer in at risk subjects of the same kindred. In clinical practice, however, besides HNPCC families, there are families with multiple CRC patients that do not fulfil the Amsterdam criteria, or with a single case of early onset CRC, or with multiple primary tumours. These features can suggest an HNPCC syndrome. In these instances, the percentage of germline mutations of MMR genes is low and the lifetime incidence of colorectal cancer is lower than in Amsterdam families. 9 However, because of the diagnostic and prognostic value of the correct ascertainment of HNPCC families, eVorts should be made in order to identify all cases. Since the search for mutations in the hMSH2 and hMLH1 genes is time consuming, expensive, and available only at selected centres, it is important to establish alternative criteria to the Amsterdam criteria in order to select patients in whom MMR gene analysis should be undertaken. Since early onset CRC may suggest a genetic predisposition, we decided to analyse patients with onset of colorectal cancer before the age of 50, with the purpose of identifying clinical and molecular criteria that are simpler than the Amsterdam criteria, but may predict a positive outcome of genetic testing in patients suspected of HNPCC with no definitive demonstration or family history of the disease. We thus carried out molecular analysis for the detection of germline mutations of hMSH2 and hMLH1 genes, as well as MSI analysis in matched tumour and normal tissue, in 54 consecutive patients with occurrence of CRC between 20 and 50 years of age. Patients were recruited from various surgical and clinical units. Family history was not considered as an entry criterion, although the family history allowed us to separate these patients into three groups: 24 patients with no family history of CRC who were classified as sporadic; 14 patients with a family history not fulfilling the Amsterdam criteria, mostly reporting only one first degree relative with CRC or more relatives with cancer in other sites, who were classified as having a positive family history; and 16 patients whose family history fulfilled the Amsterdam criteria. Information was collected with regard to the type and site of cancer in the aVected subjects (tables 1, 2, and 3). All patients gave their informed consent for the