Abstract
identifiable. The new NHMRC guidelines out for public comment recommend follow up of patients: As multiplicity of adenomas is a strong determinant of risk of metachronous advanced and non advanced neoplasia, follow up should be at twelve months for those with five or more adenomas, and sooner in those with ten or more adenomas. The risk of colorectal cancer to relatives of patients with multiple adenomas is related to the number of adenomas in the proband – outside FAP and MYH. Therefore, as distinct from patients with small numbers of adenomas, relatives of patients with larger numbers (10 +) should be offered colonoscopy at an age relative to the age of presentation of the proband. The interval is not well defined but I would suggest 5 yearly. Hyperplastic polyposis HPS has no defined genetic basis as yet. These patients are at high risk of colorectal cancer, either through the serrated pathway or through their concurrent adenomas. Two yearly colonoscopy is advised. Although the mode of inheritance is also poorly defined, it is thought it may be recessive. Therefore siblings are offered surveillance, though usually not expected to be found with HPS themselves. There is however, a high risk of colorectal cancer in first degree relatives (siblings or parents) so colonoscopy should be offered to these relatives 5 yearly. Low level mosaicism, gonadal mosaicism, somatic mosaicism Somatic mosaicism is now well described in FAP, with respect to the APC gene; cases of multiple adenomatous polyposis may therefore be found with no germline (lymphocytic) APC mutati on. We have been searching for the same APC mutation in multiple polyps, and in
Highlights
In polyposis, the type and numbers of polyps, the pattern of inheritance, and any extraintestinal features are all important in strategic planning of the DNA mutational approach
Multiple adenomatous polyposis As a routine, we check to see if both sequencing and MLPA has been complete for APC, and full sequencing for MYH
We look for translocations by FISH analysis. If all this is negative, we move the patient to a research setting; Justine Marum is well into a PhD evaluating the role of AXIN mutations in this group of patients
Summary
Background In polyposis, the type and numbers of polyps, the pattern of inheritance, and any extraintestinal features are all important in strategic planning of the DNA mutational approach. Multiple adenomatous polyposis As a routine, we check to see if both sequencing and MLPA has been complete for APC, and full sequencing for MYH (though the return outside the three common mutations is low in our ethnic mix). Patients with multiple adenomas even without a germline mutation identified, are at increased risk of colorectal cancer; multiplicity of adenomas is the highest risk factor of subsequent colorectal cancer
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