From Miami, Florida, USA:
I have a 14 year old grandson who has just been diagnosed diabetic and put on insulin. Given the strong history of diabetes in our family, is there a reasonable probability that he has MODY, and what questions should be asked of his general physician?
He is overweight - perhaps by a factor of 2. His father is free of diabetes - as yet - but I expect him to get it. I am diabetic, as is my sister, my sole surviving sibling. My father was diabetic, as were two of his four siblings. Both my grandparents on my father's side, and several of their siblings were diabetic. Furthermore, the boys mother is half American Indian.
The combination of a family history affecting both males and females over five generations together with the obesity makes it quite likely that your grandson has one or other of the forms of Maturity-Onset Diabetes of the Young (MODY).
At the moment, the most important goal is to achieve the best possible control of his blood sugar rather than to be overly concerned for a precise diagnosis. Nevertheless I can see some reasons why it might be worth the time and expense to achieve an exact diagnosis. The first is for prognosis. MODY2 or glucokinase deficiency, a chromosomal abnormality on chromosome 7, usually has a mild course with a minimal tendency to vascular complications and usually doesn't require insulin. Several variants of this genetic abnormality have now been described. MODY1 and MODY3 are chromosomal abnormalities on chromosomes 20 and 12 of what are called the hepatocyte nuclear factors 4a and 1a. These forms of MODY are more vulnerable to long term complications and more likely to need insulin.
A second reason for exact diagnosis could be for genetic counselling within the family.
The third reason, of course, is to explore the possibility that your grandson may not require insulin after all. Perhaps the most expeditious way to deal with this is to ask your doctor about getting an antibody test and details of how to get this done can be obtained for the DPT-1 office at (800) 425-8361. If he has antibodies he has autoimmune Type 1 Diabetes and will need insulin for the rest of his life or until transplants become greatly more practicable. If he is antibody-negative, then the possibility of confirming MODY is increased especially if there is any African American or Hispanic inheritance in the family. Because there is no element of insulin resistance in any of the forms of MODY the next stage in diagnosis would be to do an intravenous glucose tolerance test with insulin levels and a test of insulin secretion rates during a graded glucose infusion. This would enable a differentiation from Type 2 Diabetes. Such a plan would almost certainly have to be negotiated in a specialised research Center and so of course would the ultimate determination of a specific chromosomal abnormality.
Finally, MODY is uncommon, probably less than 1% of all diabetics below age 20; but a significant proportion undiagnosed. Amongst all insulin dependant diabetics this group comprises 2-5%.
I hope this gives you a glimpse of the complexity of diagnosis; but also gives some encouragement to see if insulin may not be absolutely necessary for good control.
Additional Comment from Dr. Lebinger:If your grandson had ketones in the urine and had already lost some weight when he was diagnosed with diabetes, most likely he does not have a form of MODY and will need insulin treatment. If he did not have ketones in the urine and had not lost any weight prior to diagnosis, then further testing is necessary to decide if he has a form of MODY or early Type 1 (Insulin Dependent) Diabetes.
[Editor's comment: It's not clear from your question if your grandson has been under the care of a pediatric endocrinologist as well as a General Practitioner. If he's not, he ought to be. This is a rare situation, and requires specialized evaluation, as discussed by Dr. O'Brien in his answer. WWQ]
Original posting 8 Jun 97
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