A Labour MP has said inbreeding may be partly to blame for a rise in diabetes cases in his constituency in Norwich.
Inter-family relationships could have led to a sharing of a gene linked to the condition, former science lecturer Dr Ian Gibson told BBC Radio Norfolk.
"There may be some degree of familiarity, family relationships, in terms of brothers and other families with the same name and so on," he said.
But a consultant at a local hospital said the remarks were "disgraceful".
"It's an insult to people with type-1 diabetes and their families and it's an insult to people in Norfolk," said Dr Ketan Dhatariya, a diabetologist at the Norfolk and Norwich University Hospital.
"There's no suggestion that that is the case. It's not the way that genetics works," he told the Eastern Daily Press newspaper.
"There is a genetic element, but it may be triggered by an environmental factor. Nobody knows why it is rising."