Nature Or Nurture? Is It Genes Or The Environment Which Causes Type-1 Diabetes?

Type-1 diabetes - the condition in which blood sugar levels lose their automatic control, which usually comes on at school age and which requires injections of insulin every day - is an auto-immune disease, meaning that the cells which should be making insulin (in the pancreas) are mistakenly attacked and destroyed by one's own immune system.

No-one knows why, but white blood cells of the immune system - which are highly specifically geared to recognise foreign molecules on microbes entering the body - confuse surface proteins on the insulin-making cells with foreign agents. These white cells, called T-lymphocytes, then latch on to the insulin-making cells and destroy them as if they were bacteria or human cells infected by viruses. It is a case of a highly sophisticated surveillance and self-protection system going awry and there's nothing the sufferer can do about it - other than artificially replace the insulin that can no longer be made by the pancreas.

Medical scientists would love to know more about the causes of diabetes, especially given that the incidence of the condition is spiralling upwards in the Western world. What makes the T cells get the wrong message? Do the pancreatic cells start producing a new protein, which joins the numerous other ones on the outside of the cell surface membrane - in which case the T-cells won't have been 'educated' much earlier in life to recognise and therefore ignore it? Or is there a change in the immune cells which makes them treat a 'friendly' protein as an 'enemy'?

Because type-1 diabetes sometimes runs in families, a plausible hypothesis is that genes are implicated. After all, it is genes which code for all the proteins made by the body and a gene could be responsible for a new protein made by the beta-cells which make insulin. In fact, around 20 different genes have been found which are associated with diabetes. These genes, however, only seem to increase susceptibility to the condition and can't cause it on their own. Studies of identical twins show that if one develops type-1 diabetes, there is only a 50% chance that the other twin will get it too. So the environment must play its part - probably in league with the forms of genes inherited from one's parents.

In a few cases, type-1 diabetes appears to be contagious: it must be more than coincidence if two or more unrelated children, living in the same home or boarding school, develop the condition within a short period. Diabetes has been blamed on viral infections, which are believed to 're-set' the immune system so that it responds inappropriately. Conversely, there is a theory that lack of infectious diseases in childhood, because of life in over-hygienic conditions and the vaccination programme, means that the immune system is not properly stimulated and this may lead to auto-immune diseases like type-1 diabetes.

The jury is definitely still out, but - as with most non-infectious illnesses - the cause is probably multi-factorial.

By: Stephen George Adams

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