Providing information for patients and professionals on research and clinical care in genetic types of diabetes.

Information for Family Members

Now the cause of diabetes has been found in at least one member of your family it is possible to offer you what we call a ‘predictive genetic test’. This test will tell you if you are likely to develop the type of diabetes that your parent or brother or sister has. You should discuss this test with your local clinical genetics team, diabetes team or genetic diabetes nursebefore you decide whether or not to have the test. The following information, as well as talking to one of the people mentioned above, may help you make your decision.

What is Maturity-onset diabetes of the young?

Maturity-onset diabetes of the young or MODY is caused by a small change in the genetic code (or gene). All your genetic information can be thought of as a library, the genes are like different books giving information on different things. The total genetic information (or whole library) largely determines how you develop, your appearance and how your body works. It is just a small change in one of these genes (or books) that causes diabetes in your family. Diabetes can be identified by repeated testing of your blood sugar (which goes up when you have diabetes) or we can find out if you are at risk of developing diabetes by ‘predictive genetic testing’.

What is a predictive genetic test?

If your parent has MODY then there is a 50% (or 1 in 2) chance that you or your brothers or sisters will have the same change in the gene as your parent and will go on to develop diabetes. A predictive genetic test looks at your genetic code (or genes) to see if you have the same change that causes diabetes in a member of your family.

What does the predictive test involve?

The test involves having a blood sample taken from your arm. This can be taken locally and sent to us in the post.

What happens to the blood sample?

The blood sample is sent to the molecular genetics laboratory at the Royal Devon and Exeter Hospital where the DNA (or genetic information) is removed from some of the cells in the blood. The DNA will be examined to see whether or not you have inherited the same change in the gene as your family member who is known to have diabetes. Any remaining DNA is stored in a freezer.

Will other tests be done on the blood sample or DNA?

The blood sample you give will only be tested for the change in the gene already found to cause diabetes in one of your family members. The sample will not be tested for any conditions other than diabetes.

How will I find out the result?

The result is usually ready within 1-2 months of us receiving your blood sample. The result will be sent out to the doctor or health care professional who referred you. You will be given an appointment to discuss the result.

What are the possible results of a predictive test?

You could either have a ‘positive’ or ‘negative’ result. A ‘positive’ result means you have inherited the same change in the gene as your family member with diabetes. This means you are very likely to develop diabetes during your lifetime, however we cannot be sure when the diabetes will actually develop this is usually before 20 years and can be as young as 6 years but may not be until your 30’s or 40’s. We would suggest having a yearly blood sugar check with your GP, you could also watch out for any of the symptoms of diabetes such as thirst, passing a lot of urine or losing weight without trying. If you had any of these signs then you should also go to your GP for a blood sugar check. A ‘negative’ result means you have a normal copy of the gene. This means you have no more chance of developing diabetes than anyone else in the population and do not need regular check ups.

What if I choose not to have a predictive test?

You may choose not to have a predictive test. If this is your choice then we would suggest you arrange a blood sugar test with your local GP once a year to check whether or not you have developed diabetes in the last 12 months. This would make sure any diabetes didn’t ‘get missed’. This is important because unrecognised diabetes over many years can lead to the development of health problems arising from diabetes. If you did develop diabetes you could then have a genetic test to confirm that this was the same as your family member with diabetes as this can help with decisions about the best type of treatment for you.

How can I get more information?

For more information, please contact:

Dr. Maggie Shepherd

+44 (0) 1392 40 8261