The link is far from certain, the researchers stress. However, their small study found that adult children of mothers with type 1 diabetes, in which the body produces no insulin, show a weakened response to sugar that could be a precursor of type 2 diabetes. Type 2 is the kind of diabetes that often develops in adulthood due to poor nutrition and lack of exercise, says the report in the May 31 issue of The Lancet.
"We are writing a proposal to follow a larger sample of children born to mothers with type 1 diabetes to see if they develop type 2 diabetes," says study author Dr. Eugene Sobngwi, a diabetes specialist at Saint-Louis Hopital in Paris.
It's not genetics, but something in the environment of the womb that might be responsible, the researchers say. They demonstrated that point in an ingenious way: the control group they used consisted of people whose fathers had type 1 diabetes.
"The main endpoint in our study was insulin secretion," Sobngwi says. "Twenty percent of the children born to mothers with type 1 diabetes had glucose intolerance, but none of the offspring of fathers with type 1 did."
Glucose intolerance is caused by inadequate production of insulin in response to sugar in the bloodstream. A glucose tolerance test can be used to diagnose type 2 diabetes or whether people are at risk for the disease.
When that test was given to 15 adults whose mothers had had type 1 diabetes during pregnancy, five of them showed glucose intolerance. But none of the 16 offspring of fathers with type 1 diabetes did, the researchers say.
Both genetic and environmental factors are known to contribute to the onset of type 2 diabetes. What happens in the womb could be one of those environmental factors, Sobngwi says.
There could be an effect on the parasympathetic nervous system, which regulates the activity of fetal organs, including the pancreas, which produces insulin, the researchers speculate.
Dr. Richard Jackson, an assistant professor of medicine at Harvard Medical School's Joslin Diabetes Center, calls the new theory "interesting," but he remains unconvinced.
What Jackson does find significant is that none of the people tested showed a decrease in insulin sensitivity, another significant warning sign for diabetes risk. "If what they are saying is true, you would expect that to show up," Jackson says.
Epidemiological studies haven't found a link between type 1 and type 2 diabetes, Jackson says, but those studies have not looked at the kind of relationship proposed by the French study.
And while children of mothers with type 1 diabetes are at greater risk of type 1, that risk does not depend on whether the mother's diabetes was diagnosed before or after the pregnancy, he says.