When James Marshall in Inverness placed a newspaper ad for diabetics who were suffering terrible side effects since switching from animal to human insulin, six of the 30 people who wrote had developed multiple sclerosis like symptoms within months of making the change.

His own son, Stephen, now 27 a diabetic for 14 years went from having his condition well under control to suffering fit like hypos, stroke, ataxia (loss of co-ordination), before finally being diagnosed as having MS. Marshall says: "Now he can't walk unless I support him. He can't stand without help." Stephen has now switched back to animal insulin and, although his diabetic control has returned, he remains disabled.In Borehamwood, Joe Cooper's daughter also now apparently suffers from MS and uses a wheelchair. Within six months of switching to human insulin, her health began to deteriorate dramatically: she was diagnosed as having ataxia, epilepsy, a number of minor strokes and MS before going on to suffer a heart attack which, thankfully, she survived.

Since it was introduced 10 years ago, human insulin has become associated with a catalogue of side effects, most commonly the loss of warning signs of an impending hypo and increased severity of attacks.

Paul Lewis, 39, a diabetic since 1962, says he went from around four hypos in 24 years to having four or five a week after switching. Fit like hypos, where he would foam at the mouth, would strike without warning, to the point where he, too, was told he was epileptic a diagnosis eventually refuted by a neurosurgeon. In August 1989, he was in a diabetic coma for five days. He says he also suffered memory loss (which was written off by doctors as depression) and searing pain in his limbs. The pain and his other side effects subsided since reverting to animal insulin.

Lewis and Marshall went on to set up the National Diabetic Federation (see below) and say they now know of 30 diabetics where MS was diagnosed within a few months of switching insulin. They believe that human insulin can trigger a condition which is being mistaken for MS.

Yet the British Diabetic Association remains sceptical of any claims of problems. One of its medical spokespeople told WDDTY: "I haven't seen any data which suggests there is an excess number of diabetics with MS. You have to remember that MS is not that uncommon and having diabetes doesn't stop you getting MS."

Human insulin is, of course, not human at all but genetically engineered to resemble true human insulin."It was felt that if it is possible to produce something which is identical to the insulin the human body produces, it is better to use that than something designed for cows or pigs [the two sources of animal insulin]", says the BDA spokesperson. "In fairness, there is no proven benefit except in a few cases."

However, writing in the British Medical Journal, Liverpool based doctors Gareth Williams and Alan Patrick (BMJ, 8 August 1992) identify a difference which could begin to explain the range of neurological complications associated with human insulin. "Human and porcine insulins differ in only one out of 51 amino acid residues; although apparently trivial, this change evidently affects the physiochemical and pharmacokinetic properties of the molecule, as porcine insulin is more lipophilic than human insulin." "The more lipophilic porcine insulin could gain access to the brain more readily and, in theory, could modulate the effects of low glucose concentrations on hypothalamic or other neurones."

They add: "A direct effect of insulin on the human brain is suggested by the recent demonstrations that counterregulatory hormone responses and symptoms differ when comparable hypoglycaemia is induced by high or low insulin concentrations." In other words, it may not just be the level of your blood sugar alone which determines the impact of a hypo.

The National Diabetic Federation can be contacted on (0942) 833389 for advice or legal information.