My son was diagnosed with type 1 in early 2011. Since then, we have had to decrease his insulin twice. He started on 19 units of Lantus, 19 units of fast acting insulin, is now down to 12 units of Lantus, with 6 units of fast acting insulin. His most recent A1c was 6.4. His insulin dose is 0.35 units/kg and is blood sugars are very well balanced. Our nurse now suspects he has MODY, but is not sure. How can we determine this? My father, the only other family member with diabetes, has adult onset type 2.

This is a difficult question. Optimally, islet cell antibody, GAD-65 antibody and insulin antibody 2 could be checked at diagnosis or any time afterwards. If one or more were positive, then this would represent type 1 autoimmune diabetes mellitus in a teenager. However, about 20 to 30% of kids will be antibody negative so this is not definitive if negative, only if positive. Whether positive or negative, most Caucasian teenagers have type 1 diabetes. However, for those of African, Asian or aboriginal origin genetically, this information may not be the same. That is where the type 2 diagnosis or the MODY diagnosis must be entertained. There are specific genes that can be tested to see if they are similar to the MODY genotypes but they are expensive. Your physician would know where this can be sent. With DKA at diagnosis or with high ketonuria, this also favors type 1 rather than other types of diabetes. However, there are exceptions to all these “rules.”

Most likely, this is type 1 diabetes with a prolonged honeymoon period where the damaged pancreas works for some months and therefore there is stable glucose control and an excellent A1c. This lasts for about 3 to 6 months in many teenagers but occasionally lasts for a few years. We do not fully understand why this happens only occasionally although tight glucose control regimens seem to help make this happen more often and for longer duration. At this point in time, the best advice is usually to stay doing what you are doing successfully, use the insulin and make adjustments according to frequent blood glucose monitoring pre and post meals as a guide to optimize results. If this is “just” a honeymoon phase that will end when it is “ready to end,” then you will know this by the rising blood glucose readings and insulin needs increasing. My professional advice is that you do not have to spend so much money for expensive genetic tests (or even only moderately expensive antibody tests) since time will answer the question of how much insulin and how difficult or easy is the control. If this were a research question, these would all be very important for statistical and demographic purposes but for caring for your child, I don’t think that the extra money gives enough information to warrant such spending except out of curiosity.

SB