Autism is much more visible these days -- just last month the CDC reported that 1 in 88 children has been diagnosed with an autism spectrum disorder -- but despite earlier and more accurate diagnoses, we’re still largely in the dark about why some kids have it and others don’t. Every so often a study will come out implicating a new risk factor, but most of the time it turns out to be largely media hype rather than the big breakthrough we’ve been hoping for.
Studies looking at identical twins have found concordance rates of around 60-90 percent -- high enough to tell us that genetics certainly play a large role, but still low enough to suggest that environmental factors also matter. Many potential risk factors have been identified through observational studies, but most of their effects are modest. Just a few of these risk factors include parental age at birth, use of medication (specifically of psychiatric medication during pregnancy), having a multiple birth and even being born in the summer.
Another one of these risk factors is gestational diabetes, which was previously shown to double the risk of a woman having an autistic child. Because diabetes is characterized by a resistance to insulin, researchers decided to look at another metabolic condition with this hallmark: obesity.
In a new study, published last week in the journal Pediatrics, researchers at UC Davis followed a group of 1,004 children and their mothers over the course of seven years. This group included 517 kids with an autism spectrum disorder (ASD), 172 kids with another developmental disorder (DD) and 315 control children with neither disorder. As expected, they found that more mothers had either Type 2 or gestational diabetes during pregnancy in the DD group (11.6 percent) than in the control group (6.4 percent). And after adjusting for other factors that might explain differences between these groups, they found that mothers with diabetes were 2.3 times more likely to have a child with a developmental disorder. They also saw more diabetes in the ASD mothers (9.3 percent) than the control group, but the numbers were not statistically different.
What’s new about this study, though, is that they also looked at whether obesity was associated with an increased risk of having a child with an ASD. They found that obese women had a 67 percent higher risk of having a child with an ASD, and the risk of having a child with another DD more than doubled.
Although this study does not address how these two related metabolic conditions might contribute to autism and other developmental disorders, the researchers think one possibility may be that fetal exposure to excess glucose could lead to increased oxygen consumption and iron deficiency, either of which could have negative effects on brain development. Another possibility relates to the chronic inflammation seen during both obesity and diabetes, which could lead to chemical regulators of the immune system crossing the placenta and potentially disrupting brain development (but this has only been seen in animal studies so far, so it’s not yet known whether human development would be affected in the same way).
It’s also possible that something common to women with diabetes and obesity that wasn’t directly examined in this study is actually influencing the risk for these disorders. Even so, with one third of women of childbearing age obese today, understanding what’s driving these associations will be an important research question to consider with potentially large impacts on public health. Read more about the study here.