A rare, hereditary form of autism has been found — and it may be treatable with protein supplements. Genome sequencing of six children with autism has revealed mutations in a gene that stops several essential amino acids being depleted. The mutations are likely to account for only a very small proportion of autism cases. The children in the study came from three families with Middle Eastern ancestry; in each case the parents were first cousins. Studying such families makes the hunt for the rare recessive mutations underlying some forms of autism simpler than it would be among the general population.
In each family, the research team identified mutations that inactivate the enzyme BCKD-kinase, which normally prevents the body from breaking down branched-chain amino acids called leucine, isoleucine and valine after a meal. Humans cannot synthesize these amino acids and must obtain them from food. Thus, after eating, the children have low blood levels of the branched-chain amino acids. How this deficiency causes autism is still a mystery. Branched-chain amino acids enter the brain through specialized transporters in the fortress of brain-protecting cells known as the blood–brain barrier. The transporter proteins also shuttle other large amino acids into the brain, and when levels of the branched-chain amino acids are low, more of these other large molecules get through.
The research team has tried supplementing the diets of the children with this form autism, using muscle-building supplements that contain branched-chain amino acids. The researchers found that the supplements restored the children's blood levels of branched amino acids to normal. As for their autism symptoms, the “patients did not get any worse and their parents say they got better, but it’s ”anecdotal”.