The FAP Gene

Bharati Bapat, PhD - Department of Pathology, Molecular Diagnostic Laboratory

Have you ever wondered why some of us are tall while others are red-haired or blue-eyed? Packets of genetic material called genes not only determine our looks but also our likelihood of diseases.

However, with about 50,000 to 100,000 genes in every cell in our body, scientists are trying to sort out the 10% of genes causing inherited diseases which can be passed on from one generation to the next. It is hard to imagine but over 4500 genetic diseases have been identified through altered genes. Although many of these diseases are considered rare on their own, many lives can be touched because of the hereditary risk to children and siblings of an affected individual.

How do scientists find genes in the first place? Genes lie along thread-like structures called chromosomes, strung like beads. There are 46 chromosomes in each cell in our body which contain all the instructions for making a human being. We receive two copies of every gene, one from our mother and one from our father. Finding chromosomes is the same as finding cities on a map. Since the distance between cities can be great, we look for landmarks to make our trip easier. Scientists also need some way to pinpoint where they are going when searching for genes. They try to locate markers on each chromosome to help them find their way. Once a gene is identified on a chromosome, scientists can find out what it does and why it went wrong.

In 1991, the gene for FAP was discovered. Although patients carry one copy of the disease gene from each parent, a defect in one copy of the gene causes the disease. A clear pattern caused by a single gene emerged so that each child of someone with FAP has a 50% chance of inheriting or not inheriting FAP. The gene is found on chromosome #5 of the 46 chromosomes and we now know many markers around this large gene. If these markers are very close to the gene, there is an increased chance that they are passed on together from the parent to the child.

A test has been developed to determine who is and who is not at high risk of FAP. The genetic test may tell us the probability of a "high" risk for an individual before clinical symptoms may develop. In many instances, test results may lead to feelings of guilt, sadness, or anger among family members. It is important to know what the test can and cannot do. A genetic counsellor is trained to talk with families beforehand about the test implications and afterward about the results.

Patients can learn how to reduce the genetic risks for their children and siblings. They can find out the chances of developing a disease and understand how an inherited disease can affect another generation. Knowing where to obtain medical information about the disease, its treatment, and available resources can make all the difference for affected families.

This research is exciting because it will allow doctors to save lives through early diagnosis. In the future, it may be possible to repair the faulty gene or even turn it off. Scientists believe the FAP may help us answer the riddle of hereditary bowel cancer and bowel cancer in the general population. By studying a precancerous disease like FAP, we may develop a model to control other types of cancer.