A study of people born without a pancreas has provided a "key" which could help those with Type 1 diabetes.
The discovery of a defective gene - GATA6 - was made by Peninsula College of Medicine and Dentistry researchers at the University of Exeter.
The gene is vital to the development of the pancreas, which produces insulin cells to regulate blood-sugar levels.
It is hoped the GATA6 discovery could help lead to stem cell treatments for Type 1 diabetics.
Type 1 diabetes is a genetic auto-immune disease in which the body's own defences attack and destroy pancreatic beta cells.
Because their pancreases cannot produce insulin, patients have to inject themselves with insulin to stay alive.
Andrew Hattersley, professor of molecular medicine at the Peninsula College, said until now nobody had realised how crucial GATA6 was to the production of insulin-producing beta cells.
"If you want to give Type 1 diabetics back the cells they've lost, you have to open the right doors and what we've found is the key to the first door," he told BBC News.
"Of all our discoveries, this could perhaps be the more relevant to people with Type 1 diabetes."
The professor said finding that "key" was almost like trying to find one misspelled word in a library.
"If you didn't know where the spelling mistake is, the old fashioned way was to check every book," he said.
"But with the new genetics approach - checking the whole genome - you can check the whole library in one go."
The defective gene was found in a child born without a pancreas [pancreatic agenesis], to parents with healthy insulin-producing organs.
"Anything found in the child and not in the parents and you know that's where the problem is and that's where we found that first key," he said.
"This rare genetic condition has provided us with a surprising insight into how the pancreas develops.
"Our study suggests that GATA6 plays a very important role in this process and we hope this will help the crucial work to try and make beta cells for patients with Type 1 diabetes."
Prof Hattersley said his hope was that the discovery could eventually help people living with Type 1 diabetes throughout the world.
Stem cell treatment would not, however, help patients with Type 2 diabetes. This is not genetic, but linked to lifestyle and obesity.
The Peninsula research has been published in the journal Nature Genetics.