Phenotypic characteristics of colo-rectal cancer in I1307K APC germline mutation carriers compared with sporadic cases.

The I1307K APC germline mutation is associated with an increased risk to colo-rectal cancer (CRC). Whether and to what extent the phenotype of CRC in mutation carriers differs from sporadic cases, remains unknown. To gain insight into this issue, we analysed 307 unselected Israeli patients with CRC, who were treated in a single medical centre, for harbouring the I1307K mutation. Twenty-eight mutation carriers (9.1%) were detected. Two of 28 mutation carriers (7.1%) and 93/277 (33.6%) of non-carriers, were of non-Ashkenazi origin (P < 0.01). In 74/278 (26.6%) of the sporadic cases, and only 1/28 (3.6%) of mutation carriers (3.6%) the tumour was located in the right colon (P < 0.01). Mutation carriers had a more advanced disease stage (14/28 - 50% Dukes C), as compared with 60 (19.5%) of non-carriers (P = 0.02). The mean age at diagnosis was similar: 65 (+/- 9.7) years and 66.3 (+/- 11.6) years, for mutation carriers and non-carriers, respectively. No statistical differences were noted between the two groups in sex distribution, tumour grade, and family history of cancer. We conclude that early age at diagnosis and family history of cancer cannot be used to predict who is likely to harbour the I1307K APC germline mutation carriers. However, the tumours in patients with this mutation appear different than those without, are less likely to be proximal and more likely to be advanced than tumours in non-carriers.

The I1307K APC polymorphism: prevalence in non-Ashkenazi Jews and evidence for a founder effect.

A missense mutation within the APC gene, I1307K, was described in Ashkenazi individuals at risk for colorectal cancer (CRC) and in the general population. The anecdotal reporting of the occurrence of this mutation in some non-Ashkenazi individuals led us to hypothesize that within the Jewish people, the I1307K polymorphism may reflect a founder mutation, and that the mutation is not restricted to ethnic Ashkenazis. To test that notion, and to establish the occurrence rate of the I1307K polymorphism in non-Ashkenazi Jewish populations, we screened Iraqi and Moroccan Jews and consecutive Jewish CRC patients and performed haplotype analysis with APC-linked markers in two I1307K carrier families. We analyzed Jewish individuals: 210 Moroccans, 160 Iraqis, 148 Ashkenazi, and 349 CRC patients (227 Ashkenazi and 122 non-Ashkenazi). The mutation detection scheme included PCR followed by denaturing gradient gel electrophoresis (DGGE) or modified restriction analysis (MRA). Haplotypes were assessed using three intragenic and three flanking markers. The I1307K polymorphism was detected in 29/227 Ashkenazi (12.8%), 2/122 (1.6%) non-Ashkenazi CRC patients, and in 2 individuals each (approximately 1%) within the Moroccan and Iraqi populations. Allelic pattern analysis in all our I1307K carriers, revealed a common haplotype for the three intragenic markers tested, in all mutation carriers, regardless of ethnic origin. The I1307K polymorphism, therefore, exists in all ethnic Jewish populations: Ashkenazi and non-Ashkenazi, with or without colon cancer. Jewish I1307K mutation carriers share a common allelic pattern with APC-linked markers. This strongly supports the notion of a founder mutation for I1307K.

Common origin of the I1307K APC polymorphism in Ashkenazi and non-Ashkenazi Jews.

A common germline missense mutation within the APC gene, I1307K, has recently been described in Ashkenazi Jews. We detected this polymorphism in two non-Ashkenazi Jewish women using denaturing gradient gel electrophoresis (DGGE), and hypothesized that in Jewish individuals it might not be restricted to Ashkenazim, and actually reflect a common ancestral polymorphism. To test this notion we performed allelic pattern determination using APC-linked markers in these two women and in nine Ashkenazi carrier controls. The pattern of the intragenic markers, as well as a single downstream marker 30-70 Kb from the APC gene was identical in all individuals, regardless of ethnic origin. We conclude that the I1307K polymorphism in Jewish individuals, is not restricted to Ashkenazim and probably reflects a founder mutation.