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From New Jersey, USA:

I really have two questions and I hope that you won't be offended by the nature of one of them. My boyfriend has Type 1 diabetes and our relationship is becoming quite serious. Unfortunately, he suffers from occasional impotence. What can be done about this (besides, of course, Viagra, but I'm not comfortable with the idea of him taking unnecessary medications)? Will it get worse? He's 23 and was diagnosed at age 16.

My other question relates to our potential progeny. There is no evidence of diabetes in my family so I don't believe that I am a carrier. Does diabetes follow a "Punnett" distribution for recessive traits? That is, not exhibited but carried in the F1 generation? Is it autosomal or sex-linked?

Can you recommend a web-page that would be somewhat technical in nature that will address some of these types of questions?


Impotence is an important and fairly common complication in male diabetics. It is however unusual for it to be a consequence of neurological or vascular problems when the diabetes has been present for less than ten years. Nonetheless, the first step to setting matters right is to make sure that blood sugar control is pursued to the point of reaching hemoglobin A1c levels that are at the upper range of normal. What is also probable though is that there is some psychological basis for the problem and this will take the utmost in tact and sensitivity to resolve, something you should try to achieve with the help of your friend's doctor. In the meantime and given that the problem is occasional and the subject in his 20's Viagra may in fact be the best approach. If control has in fact been poor over the early course then it may be necessary to embark on a more elaborate workup using a specialised clinic. Certainly any evidence of early complications for example, microalbumin, etc. need to be treated.

The inheritance of diabetes is a good deal more complex than can be interpreted on simple Mendelian principles. First of all, different subtypes of the disorder may reflect changes in a number of nuclear chromosomes as well as in mitochondrial DNA. The genes that confer susceptibility to Type 1A or autoimmune diabetes lie in the short arm of chromosome 6.This region contains nearly 200 genes most of which have some influence on the immune system. The most important lie in the HLA (Human Lymphocyte Antigen) region and produce a group of molecules characterised by a DR or DQ prefix which lie in a special locus on an antigen presenting cell and may bond to activated CD4 lymphocytes to produce clinical diabetes. The highest risk for Type 1A Diabetes is associated with individuals with amino acid chains identified with the expression DQA1*0501-DQB1*0201 and DQA1*0301-DQB1*0302 with DRB1*0401 or 0402.

It is important to remember however that the genetic endowment only confers susceptibility and that there is an additional and so far unknown environmental component that triggers actual clinical diabetes. One of the factors has been thought to be linked to the amount of cow's milk consumed that contains a variant protein called A1 beta casein.

Since you say that you are prepared for a certain amount of technical information there are two web sites that you might consult the first is and then go to Chapter 7. The second is in PubMed; if you search under 'diabetes,genetics' you will see 12 down on the first page an article by Morwessel. If you then click on 'see related articles' you access a good deal of relevant information.

The chance of a Caucasian child in the U.S. getting Type 1A diabetes before age 18 if the father is diabetic is around 7%. It is a little lower if the mother is diabetic.


Original posting 17 Apr 1999
Posted to Complications and Genetics and Heredity


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