The exact cause of autism is unknown, but scientists generally agree it’s a result of abnormal brain structure and function often due to genetic factors. Scientists have hypothesized that the environment, in addition to genes, may be at play, including a lack of vitamin D, lead or mercury exposure, and viral infections, though the evidence to support many of these theories is weak. Some thoeries are even wildly inaccurate, such as the idea that vaccines cause autism.

But researchers are currently exploring one other avenue of study — the idea that diet, or certain nutritional supplements, may play a role in either the development or the treatment of autism. One recent study out of the Texas A&M Health Science Center College of Medicine focused on carnitine, a compound that is made naturally in the body but can also be received from certain foods — particularly fish, eggs, milk, and red meat. Carnitine can be taken as a dietary supplement for medical reasons, or even for bodybuilding.

The study, published in the journal Cell Reports, examines how carnitine as a prenatal supplement could act as protection against autism development. Carnitine is important because it helps transform fat into energy, which is used by many aspects of the body, including the muscles, heart, and brain. While it’s produced naturally by the body, some people may not have enough of it — particularly those who suffer from angina or or intermittent claudication, according to the University of Maryland Medical Center.

In some cases, people have a mutation in the TMLHE gene for an enzyme that produces carnitine, resulting in no carnitine production at all. Past research has found that a specific subgroup of mildly autistic boys were three times more likely to have this mutation in the TMLHE gene compared to non-autistic people. The theory is that a lack of carnitine in autistic patients exacerbates symptoms by causing defects in neural stem cells in the brain.

“Inborn errors in carnitine production cause significant issues in a cell type one would believe has to contribute to autism risk,” Vytas Bankaitis, the E.L/ Wehner-Welch foundation Chair in Chemistry at the Texas A&M College of Medicine and an author of the study, said in the press release.

In the latest study, the researchers worked on a new technology that could measure and analyze individual neural stem cells and their defects in the brain, whereas in the past conventional technology couldn't detect them.

“It’s very difficult to study neural stem cells in their complex natural environment,” Zhigang Xie, assistant research scientist at the Texas A&M Health Science Center College of Medicine and an author of the study, said in the press release. “But now we have a technology that makes such studies possible.”

They found that neural stem cells that can’t produce carnitine create a load of problems for the developing brain. When the researchers implanted carnitine into the lacking neural stem cells externally, however, the cells behaved normally — suggesting that carnitine supplements during a child’s development in the womb could potentially prevent autism, but only certain types.

"Even if this strategy works, it will not be a panacea for reducing all autism risk," Bankaitis said in the press release. "While it could work in cases involving carnitine-deficiency, other pathways are also in play because as many as 1000 genes might ultimately be found to relate to autism risk. Still, the potential impact of even such a limited preventive strategy could be significant as mutant TMLHE alleles are surprisingly common in the human population."

According to Autism Speaks, a 2012 study on carnitine’s link to autism found that the defect only affected a very small number of people with mild autism, and more research is needed to understand the link. And it’s possible that the carnitine defect is merely an association; researchers still aren’t sure whether it directly causes autism.

The ‘Autism Diet’

The carnitine study brings up questions about diets in general when it comes to autism. Some scientists have hypothesized in the past that diet and nutrition can, indeed, contribute either to the development of autism or its treatment — and their theories expand beyond carnitine.

For example, “autism diets” are more popularly known as gluten-free and casein-free (GFCF) diets. While some scientists laud the efficacy of these diets, others remain skeptical — especially since these diets may be lacking in other important nutrients. In addition, a gluten-free diet is typically only beneficial for people with celiac disease or a gluten intolerance; it’s not healthier for regular people, and there’s little evidence to support the notion that such a diet treats autism. In fact, some studies have gone so far to say the GFCF diet has absolutely no benefit for children with autism.

When it comes to carnitine, however, more research will help us better understand the link. “For some individuals, this simple nutritional supplement might really help reduce the risk of developing autism spectrum disorder,” Xie said in the press release. “Any progress on the prevention front would be welcome given the number of people affected.”

Source: Xie Z, Bankaitis V, et al. Cell Reports, 2016.