My 35 year-old fiance has juvenile diabetes. Can diabetes be inherited? If so, what are the chances of our children developing diabetes?
Recently studies have begun to see if insulin dependent diabetes can be accurately predicted and prevented in close relatives of people who already have this condition. We don't completely understand what causes this type of diabetes. What we do know is that in most individuals with insulin dependent diabetes, their pancreas has been failing for months to years before their blood sugar becomes abnormal. Diabetes seems to be an "autoimmune" condition. This means that the body has made antibodies against its own pancreas which have caused it to slowly stop making insulin. (Normally the body only makes antibodies against something foreign to the body. For instance the body normally makes antibodies against viruses and bacteria to prevent us from getting sick. Or if you receive a transplanted organ from someone else, your body will make antibodies against it and reject it unless special medication is given to prevent antibody formation and rejection.)
We don't know why the body "makes a mistake" and starts making antibodies against its own pancreas (or more specifically, against the islet cells of the pancreas. The islet cells make insulin.) We think you must inherit the tendency to make antibodies against your own pancreas. Diabetes is more common in people who have close relatives with this condition. If you have a close relative (a parent, sibling, or child), you have a ten times greater risk of developing diabetes than if you don't have any close relatives with diabetes. That is why we say diabetes is an inherited or genetic condition. It is more complicated than other inherited conditions. Actually, most people who develop insulin dependent diabetes do not have a close relative with diabetes. Even though your risk of developing Diabetes is greater if you do have a close relative with diabetes, than if you don't, the risk is low compared to other inherited conditions. (You have a 3 to 10% chance of developing it if you have a close relative.) If one identical twin develops insulin dependent diabetes, the other identical twin only has a 35 to 50% chance of developing diabetes. The other twin should have almost a 100% chance of developing diabetes if genetic inheritance were the only issue.
We think there may be viruses or chemicals in the environment that may trigger diabetes if the individual has inherited the susceptibility to this condition.
Several viruses have been thought to possibly trigger diabetes. The most common ones are mumps and Coxsackie viruses. We think that possibly these viruses can attack the pancreas, cause an inflammation, and trigger the body to make antibodies against the islet cells which, months to years later, causes diabetes when the pancreas can no longer make enough insulin to keep the blood sugar normal.
Recently, there have been reports suggesting that feeding babies formula made from cow's milk may trigger diabetes in individuals who have inherited the susceptibility. It seems that some of the proteins in cow's milk may be similar to some of the proteins on islet cells. If babies are fed cow's milk protein at a young age, they may make antibodies agains the cow's milk protein which may also attack their own islet cells and destroy them, causing diabetes.
Studies are planned to see if avoiding exposure to cow's milk protein in the first 6 to 12 months of life will help to prevent diabetes. It has been reported from Finland (where diabetes in children is more common than in other parts of the world), that children who were only breast fed, have less chance of developing diabetes later in life.
Since we now know that the the process leading to diabetes may take months to years, we are trying to identify individuals whose islet cells are being destroyed before their blood sugar becomes abnormal and try to prevent the complete destruction of the islet cells before they develop diabetes.
Right now, studies to predict and prevent diabetes are mainly being offered to individuals with close relative with diabetes. To predict which relative will prevent diabetes, first a blood sample is checked for antibodies against islet cells and/or insulin. If this is abnormal other studies can be done to identify which of these individuals are at the highest risk of developing diabetes. The most common test is an IV glucose tolerance test (not an oral glucose tolerance test, which is not helpful in predicting diabetes). In an IV glucose tolerance test, glucose is given intravenously and one measures how much insulin is found in the blood several times during the next ten minutes. The blood sugar level is also measured. It turns out, individuals who are at a higher risk of developing diabetes in the next year, make less insulin than those who are at a lower risk. Interestingly, even though less insulin is made in these higher risk individuals, the blood sugar is still normal.
In the past, there have been studies to try and prevent or even cure new onset diabetes using immunosupressants (drugs used in individuals who have received an organ transplant to prevent rejection by preventing the body from making antibodies), These studies have not been successful.
At the present time, there are two main large ongoing studies to try and prevent diabetes. One study which is mainly being carried out in Europe is using oral Nicotinamide. This is a B vitamin which may help prevent the islet cells from being destroyed by the antibodies.
In the United States, insulin is being used to try and prevent diabetes. Studies in animals suggest that giving insulin either by injection or orally may help to prevent diabetes either by preventing the body from making antibodies or protecting the islet cells from being destroyed by the antibodies.
Individuals who have been identified as being at a high risk of developing diabetes will be invited to participate in a national study (DPT-1). There are two parts to this study. Patients identified as having the highest risk of developing diabetes by the blood studies, will be invited to participate in a trial of combined subcutaneous and Intravenous insulin treatment to try and prevent the diabetes from developing. Half of these individuals will be treated with insulin injections twice a day in addition to continuous IV insulin for 4 days once every year. Half will receive no insulin to see if the treatment decreases the risk of developing diabetes. Individuals ranging in age from 4 to 45 are eligible to participate.
The second part of the study is for individuals identified by testing as being at a slightly lower, or "intermediate" risk of developing diabetes. They will be invited to participate in a study using oral insulin to try and prevent diabetes. Half the individuals will take capsules containing insulin daily, and half will take "placebo" capsules containing no insulin. Individuals ranging in age from 3 to 45 areng no insulin. Individuals ranging in age from 3 to 45 are eligible to participate.
Original posting 15 Apr 96
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