These include the very rare polymerase proofreading associated polyposis (PPAP) syndromes and patients who grow adenomatous polyps but where we cannot find a genetic cause.
Polymerase Proofreading Associated Polyposis (PPAP)
The POLE and POLD1 genes. In 2013 Nature Genetics published findings of two newly identified genes POLE and POLD1 that had been linked to cancer and bowel polyps in some families. Both genes are involved in the process of copying DNA in the body.
How is PPAP inherited?
PPAP is dominantly inherited so if there is an alteration in one of the two copies of either gene in our bodies, this may stop the gene working properly and may cause that person to have a higher chance of developing certain cancers.
What are the clinical features of PPAP?
Patients may grow adenomatous polyps in the large bowel and there seems to be an increased risk of other cancers such as breast, endometrial and duodenal cancer.
What checks are advised?
Due to the rare nature of the condition, we cannot be certain of the exact nature of cancer risk and we look after each patient on an individual basis. Usually this condition is managed endoscopically with regular checks of the large bowel (colonosocpy), stomach and duodenum (gastroscopy). Some families may need additional checks depending on their family history of cancer and recommendations will be given based on current published research.
Adenomatous Polyposis with no genetic alteration identified
In around 20% of patients who develop adenomatous polyps we will not be able to identify a genetic alteration causing these polyps. In some cases, only a handful of polyps grow and it is only the presenting individual that needs screening. In other cases, the patient grows hundreds of polyps and exhibits signs exactly like FAP. When a genetic cause cannot be identified, the diagnosis is made clinically and screening and surgery is carried out according to the patient’s individual diagnosis. If a genetic cause cannot be found, this does not affect the patient’s clinical care but it does mean that if appropriate, family members will be invited for endoscopic screening and will not be able to have a genetic blood test to see if they have inherited the condition.