Monday 31 December 2012
Many individuals with multiple or large colorectal adenomas or early-onset colorectal cancer (CRC) have no detectable germline mutations in the known cancer predisposition genes.
Using whole-genome sequencing, supplemented by linkage and association analysis, specific heterozygous POLE or POLD1 germline variants have been identified in several multiple-adenoma and/or CRC cases but in no controls.
The variants associated with susceptibility, POLE p.Leu424Val and POLD1 p.Ser478Asn, have high penetrance.
POLD1 mutation is also associated with endometrial cancer predisposition.
The mutations map to equivalent sites in the proofreading (exonuclease) domain of DNA polymerases ɛ and δ and are predicted to cause a defect in the correction of mispaired bases inserted during DNA replication.
In agreement with this prediction, the tumors from mutation carriers are microsatellite stable but tended to acquire base substitution mutations, as confirmed by yeast functional assays.
Further analysis of published data shows that the recently described group of "hypermutant, microsatellite-stable CRCs" is likely to be caused by somatic POLE mutations affecting the exonuclease domain.
Dec. 30, 2012 — - Rare DNA faults in two genes have been strongly linked to bowel cancer by Oxford University researchers, who sequenced the genomes of people from families with a strong history of developing the disease.
The researchers sequenced the entire DNA genomes of 20 people from families with a strong history of bowel cancer. Eight of the 20 people had developed bowel cancer, while the rest had a first-degree relative who had developed the disease. The findings are published in the journal Nature Genetics.
They found that everyone who had a faulty POLE or POLD1 gene developed bowel cancer or had a precancerous growth in the bowel.
To confirm their findings they then looked for faults in these two genes in almost 4,000 people with bowel cancer, and 6,700 people without the disease.
Neither of the genetic faults was found in people without bowel cancer. However, 12 people with a fault in the POLE gene were found in the bowel cancer group, and one person had a POLD1 gene fault.
The POLD1 fault was also found to increase the risk of getting womb cancer and possibly brain cancer, with seven people in the study being diagnosed with womb cancer and one developing two brain tumours.
Professor Ian Tomlinson, who led the research at the Wellcome Trust Centre for Human Genetics at Oxford University, said: ‘These are two rare faults, but if you inherit them your chance of bowel cancer is high. By testing people with a strong family history of the disease for these, we can identify those who are at high risk and try to prevent the disease by using colonoscopy and other methods.’
POLE and POLD1 are genes involved in processes that repair damage to DNA. Without these genes functioning properly, affected individuals can build up damage in their DNA which accumulates and it is thought this may lead to changes that cause bowel cancer.
‘This research highlights how much more we still have to find out about the rare gene faults that can increase a person’s risk of bowel cancer,’ said Dr Julie Sharp, senior science information manager at Cancer Research UK, which part-funded the work.
Germline mutations affecting the proofreading domains of POLE and POLD1 predispose to colorectal adenomas and carcinomas. Palles C, Cazier JB, Howarth KM et al. Nat Genet. 2012 Dec 23. doi : 10.1038/ng.2503 PMID: 23263490