Why Moms Are Less Likely to Pass on Type 1 Diabetes than Dads

A child is twice as likely to develop type 1 diabetes (T1D) if their father has the condition than if their mother does, according to a recent study presented at the Annual Meeting of the European Association for the Study of Diabetes (EASD) in Madrid, Spain. Though both mothers and fathers can undoubtedly pass on genes that make type 1 diabetes more likely to develop, it appears that when women with T1D are pregnant, they also protect their growing babies from the condition.

The study confirms prior research: Fathers with T1D tend to have higher rates of children with T1D. But why? The details are fuzzy, but the research is important, because identifying what protects or reduces a child’s risk of T1D could contribute to the development of preventative treatments. Here’s a closer look at this research.

How Pregnant Women Protect Against T1D Risk

“We wanted to establish whether having a mother versus a father with type 1 gives you long-term protection or if it’s short-term,” said Lowri Allen, MD, a doctor with Wales’ Cardiff and Vale University Health Board who contributed to the new study. “For example, with an infection, a mother can provide short-term protection because of antibodies she passes to the fetus during pregnancy. After birth, a baby would eventually lose that protection over time and become more susceptible to those infections.”

Allen and her colleagues wanted to know: Does this protection from the mother ‘wear off’ or does it stay with the child long-term? 

“And if it is short-term protection,” continued Allen, “will the data show that children with affected mothers develop type 1 diabetes later compared to when they develop the condition with affected fathers?” 

But the idea of “protection” isn’t simple either. Does the age of the parent’s diagnosis matter? To answer these types of questions, the study needed both a large number of participants and a lengthy period to track the rates of T1D diagnosis.

The recent study was the largest of its kind, with nearly 11,500 participants diagnosed with T1D between the ages of 0 and 88 years old. 

The researchers’ conclusions include:

Children born to fathers with T1D are twice as likely to develop T1D compared to children born to mothers with T1D.
There is no difference in the timing of the child’s T1D diagnosis based on whether they were born to mothers with T1D versus born to fathers with T1D.
The timing of the parent’s diagnosis is important. Children who develop T1D were more likely to have a father who was diagnosed with T1D before the child was born.
Women who were diagnosed with T1D after the child was born offered no additional protection.

The bottom line is that the difference in risk has nothing to do with the mother’s or father’s genes. Rather, the key was some kind of protection offered by a mother with type 1 diabetes through the womb.

At this time, researchers still aren’t sure what protective feature the fetus is getting from the mother.

“Further research is needed to determine what it is about exposure to type 1 diabetes in the womb that is most important,” added Allen. “Is it exposure to high blood glucose levels, insulin treatment, antibodies associated with type 1 diabetes, a combination of these, or exposure to another aspect of type 1 diabetes?”

Pregnancy and Blood Sugar Levels

For a woman with T1D, pregnancy can be one of the most intense experiences due to the pressure to maintain near-non-diabetic blood glucose levels. It’s well understood that A1C levels below 7 percent are critical during pregnancy to reduce the child’s risk of birth defects and the mother’s risk of complications, like preeclampsia.

Is it possible, though, that elevated blood sugar levels could in some way protect the growing child? Even with extremely tight blood glucose management and an A1C level in the 5s, a fetus is still exposed to higher-than-normal blood glucose levels compared to a non-diabetic pregnancy.

“So this is probably the million dollar question,” explained Allen. “At the moment, it’s all very hypothetical. We didn’t have data on glycaemic management during pregnancy in this study.” 

Allen points to past research, 1999’s BABYDIAB study, in which researchers analyzed A1C levels in the pregnant woman with T1D during the third trimester and the child’s risk of developing T1D. The children least likely to develop type 1 diabetes were the ones with mothers who had blood sugar levels that were moderately elevated — not too high, not too low.

“They reported that mothers with moderate hyperglycemia, A1C levels between 5.7 to 7 percent, [conferred] a lower risk of T1D compared to those with A1C levels below 5.7 percent,” explained Allen. “But then the risk of the child developing T1D was actually higher if the mother had A1C over 7 percent.”

Allen said this could indicate that moderately elevated blood glucose levels might stimulate beta cell growth in the pancreas of the baby before birth, reducing their diabetes risk. Beta cells are responsible for the production of insulin.

“But if the higher blood glucose exposure crosses a certain threshold, then the beta cells of the child could get exhausted and that could then increase the stress on them and the likelihood of diabetes,” added Allen.  

This is just one theory. Allen said there are many others, including the idea that glucose exposure could lead to changes in the child’s DNA.

“We need to get a clear picture of how glycemic exposure affects T1D risk in the child,” suggested Allen, “and then we need to work out how we use that information in a meaningful way.” Allen and her colleagues hope the research can eventually support the development of treatments to prevent and cure T1D. 

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