Researchers at the University of California, San Diego, have identified a rare, hereditary form of autism that may be treatable with nutritional supplements, a new study reports.
The scientists sequenced the genomes of six children with both autism and epilepsy from three Middle Eastern families — in each case, the children’s parents were first cousins — and found that they had mutations in a gene that normally prevents the breakdown of certain amino acids. The end result is that children had low levels of these proteins — known as branched chain amino acids — which the body doesn’t make on its own and must be gotten through food.
Further, the researchers found, mice with the same gene mutation also showed low levels of branched chain amino acids and developed neurological problems, including tremors and epileptic seizures, related to autism. But when the mice were treated with protein supplements that restored depleted levels of the amino acids, their symptoms disappeared within a week.
“This might represent the first treatable form of autism,” Joseph Gleeson, lead author and a child neurologist at UCSD, told Nature News. “That is both heartening to families with autism, and also I think revealing of the underlying mechanisms of autism.”
The authors caution, however, that the rare mutation may contribute to only a small number of autism cases. The researchers selected the children in their study to best identify the recessive mutations involved, since there’s an increased likelihood that children from related parents will receive two copies of the mutation.
How that genetic mutation contributes to autism is unclear, but the researchers have a theory. The mutation inactivates a protein called BCKD-kinase, which prevents the breakdown of branched chain amino acids. Normally, these amino acids are ferried across the blood-brain barrier by special transporters. But when their levels drop, the transporters end up carting more of other large amino acids into the brain. These other amino acids serve as precursors for neurotransmitters like dopamine and serotonin, which play a role in mood and pleasure-seeking, and whose activities in the brain may be associated with autism.
When the research team profiled the brains of mice lacking the BCKD-kinase gene, they found very low levels of branched-chain amino acids and very high levels of these other amino acids.
“At this point, we do not know if it is the low levels of branched chain amino acids or the high levels of these other neurotransmitter precursors that lead to the autism and epilepsy features. We are trying to differentiate between these now,” said Gleeson in an email.
When the team supplemented the children’s diet with muscle-building supplements rich in branched chain amino acids, it corrected the amino-acid levels in their blood, which the researchers used as a biomarker for successful response. However, they don’t know whether the dietary supplementation will improve the kids’ autism and epilepsy symptoms over time.
“To address this question will require a longer-term study, which is why we labeled this as a ‘potentially-treatable’ form of disease,” says Gleeson. “Importantly, in the animal model we used, we found that the condition was both inducible and reversible, so we have reason to suspect that patients will improve clinically, but it remains to be proven.”
The study was published in the journal Science.