Folic acid has long been touted as an important supplement for expectant mothers, to prevent defects in the baby’s developing brain and spinal cord. It is added as a supplement to breads, pastas, rice and cereals to help ensure that women are exposed to sufficient amounts of this nutrient even before they know they’re pregnant.

In that vein, a team of scholars writing in Cell Reports suggest the supplement carnitine could protect against a certain type of autism. Some one percent of Americans are afflicted with autism, and the annual cost of autism management in the United States alone is estimated to be at least $236 billion. 

Carnitine, which the body can manufacture itself or extract from dietary sources, is required for transport of fatty acids into mitochondria—the compartment within the cell that converts these fats into energy. High levels of carnitine can be found in red meat, and one of the best vegetarian sources is whole milk. 

Other studies have suggested that inherited mutations in a gene (called TMLHE) that is required for carnitine biosynthesis are strongly associated with risk for development of autism-spectrum disorders, but why has been unclear. The new paper suggest genetic defects in the body’s ability to manufacture carnitine might be associated with an increased risk of autism if carnitine deficiency interferes with the normal processes by which neural stem cells promote and organize embryonic and fetal brain development.

The TMLHE gene encodes an enzyme that the body needs to manufacture carnitine. They suggest autism risk mutations inactivate this gene and, in the absence of their own ability to produce carnitine and without adequate outside supplementation, neural stem cells become less efficient at self-renewal. That is, when they divide, neural stem cells produce two “daughter” cells, one of which should remain a neural stem cell and the other that should differentiate. Neural stem cells confronted with carnitine deficiency too often divide to produce two differentiated cells, thereby failing to resupply the developing brain with a cache of neural stem cells.

The study’s lead author, Zhigang Xie, Ph.D., assistant research scientist at the Texas A&M Health Science Center College of Medicine, has refined a new technology that allows him to mark, follow and analyze individual neural stem cells in their native environment in a real developing brain. The researchers found that neural stem cells unable to produce carnitine don’t behave properly and are inappropriately depleted from the developing brain, but when genetically at-risk neural stem cells are supplied with carnitine from an outside source, they don’t have the same problems.

As this 'autism risk gene' is located on the X chromosome and males have only one X chromosome (females have two), that would explain why they are at greater risk. The authors say some pregnant women might absorb enough carnitine from their diet so as to make normal enzyme function less important in the context of autism risk for their babies. 

Since TMLHE's location on the chromosome is known, one possible first step for prevention is to test prospective mothers for TMLHE mutations before pregnancy, the authors say. If a prospective mother is a carrier for the mutated autism risk gene, supplementation of her diet with carnitine before and during pregnancy could help ensure that a sufficient supply of the nutrient is available to the developing embryo and fetus, thus helping to offset the genetic defect.

Source: Texas A&M