Diabetes: the genetic connections.

Insulin dependent (IDD) and non-insulin dependent diabetes (NIDD) are separate disorders. Twin studies show that IDD cannot be entirely due to genetic causes as concordance is no more than about 50%, but there is some inherited predisposition to it as shown by HLA patterns. NIDD, on the other hand, is predominantly due to genetic causes since identical twins are nearly always concordant. Many cases of NIDD show chlorpropamide alcohol flushing (CPAF), a dominantly inherited feature which may precede the appearance of diabetes and thus act as a genetic marker for this type of diabetes. Diabetics who show chlorpropamide acohol flushing are less likely to develop retinopathy than those who do not. Genetic factors must therefore affect the incidence and severity of diabetic retinopathy. Chlorpropamide alcohol flushing is due to sensitivity to enkephalin. Enkephalin and other opioids affect carbohydrate metabolism and insulin release. It is possible therefore that they act as neurotransmitters and cause NIDD by a sympathetically mediated effect on the liver and pancreas--in other words, that as far as NIDD is concerned Claude Bernard's views on the cause of diabetes may have been right.