You might not. In the early stages there may be no symptoms. Because early diagnosis makes such a difference to people with FAP, anyone who thinks they might be at risk should not wait for symptoms to develop, but should seek advice from their G.P.

There are 2 ways of determining if a person has FAP:

1. DNA analysis
2. Bowel screening

There have been many developments in this area.

Now that it is known that the gene responsible for FAP is on chromosome 5, it is possible to take a sample of blood, extract DNA from the sample and then test it to see if the affected gene is present or not.

The fault in the gene varies from family to family so it is necessary to find the exact faulty spot in each family. Once it has been found other individuals in the family can be tested to see whether they have got the same faulty spot. This test is more difficult to do for some families and, at the moment, does not work for everyone.

Before blood is taken for DNA analysis, a person will be offered genetic counselling. The counsellor will be able to explain the situation in more detail.

Suppose there is a suspected fault in a train and it is known that one of the bolts might be missing from under the back seat, on the left, in the fifteenth carriage. An engineer would soon be able to tell if there was a fault or not. This is like checking for a fault in a gene, in a family where the position of the fault has already been identified. But suppose nobody knows where the fault is in the train. In this case every carriage of the train would have to be examined thoroughly in order to find it. This is what has to be done when the faulty gene in a family has not yet been identified.

The check-up is straightforward. The doctor will ask questions about general health, feel the tummy and carry out a test called a sigmoidoscopy. A sigmoidoscopy involves passing a small telescope into the bottom so that the doctor can have a look to see if there are any polyps. Some people find the examination a bit embarrassing and uncomfortable but it should not hurt.

Polyps can appear in people at different ages and if nothing is seen during an examination the person may be invited to take part in a screening programme.

If during the examination, the doctors sees polyps a small sample (called a biopsy) will be taken. This is not painful and cannot usually be felt. The sample is sent to the laboratory for analysis to confirm that the polyp is an adenoma.