Viruses that cause diarrhoea and vomiting may also trigger diabetes in children with a particular genetic make-up. The finding could one day lead to ādiabetesā vaccines that might be targeted at children with certain genes.
Some children are genetically predisposed to develop type-1 diabetes, but studies of identical twins show that if one twin gets the disease, the other has only a 40% chance of developing it too, suggesting that an environmental trigger is also at work.
One suspect is a family of viruses called Coxsackie B enteroviruses (CVBs). In type-1 diabetes, the body attacks and destroys insulin-producing pancreatic cells called beta cells. It is thought that when CVBs infect beta cells, they may trigger this āautoimmunityā, but only in children with a particular genetic make-up.
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This would make sense as the genes that are linked to type-1 diabetes code for proteins involved in the immune response. However, evidence supporting the theory has relied on a small number of samples. For example, in 2007, evidence of CVB infection was reported in two of five patients with type-1 diabetes, but not in 26 non-diabetic controls.
Tell-tale protein
To test the CVB theory in a much larger group, a team led by Noel Morgan at the in Plymouth, UK, analysed tissue taken from the pancreases of 72 children who had died of type-1 diabetes shortly after becoming ill.
In more than 60% of the pancreases, they found a protein that makes up CBVās viral coating, in the beta cells. There was almost no evidence of infection in control tissue samples taken from children who had not had diabetes.
āThis is the first time that scientists have been able to provide such extensive evidence for the relationship between enteroviral infection of the beta cells and the development of type 1 diabetes,ā says Morgan.
āConservative estimateā
Although 40% of the samples did not show evidence of CBV, Adrian Bone of the University of Brighton, UK, says the people that provided these samples may still have been infected with CBV ā evidence of it just didnāt show up in the protein test. āThe protein isnāt completely stable, so 60% is a conservative estimate,ā he says.
The next step will be working out which strains of CBV trigger type-1 diabetes, and testing whether these can be used in a vaccine that prevents the disease, says Bone.
āThe study is hugely significant because for the first time we have a large enough study of pancreas post mortem samples from patients who died near to diagnosis ā this has been lacking and therefore we have had to rely on the odd case report,ā says Mark Peakman at Kingās College London School of Medicine.
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