What is the role of metabolic anomalies in the pathophysiology of autism spectrum disorder (ASD)?

Updated: Sep 30, 2019
  • Author: James Robert Brasic, MD, MPH; Chief Editor: Caroly Pataki, MD  more...
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Answer

In animal studies, dysfunction of serotonin and the neuropeptides oxytocin and vasopressin has been associated with abnormalities in affiliative behaviors. Neurophysiologic dysfunction involving 1 or more of these substances may also be present in humans with autism.

Elevations of blood serotonin levels occur in approximately one third of individuals with autistic disorder and are also reported in the parents and siblings of patients. Functional anomalies in other neurotransmitters (eg, acetylcholine, glutamate) have also been identified in some people with autism spectrum disorder. [31, 46]

Serum biotinidase is reduced in some people with autistic disorder. This enzyme is required for the use and recycling of the B vitamin biotin. Deficiency of biotin has been linked with behavioral disorders.

Immunologic studies have identified abnormalities such as decreased plasma concentrations of the C4B complement protein. Such abnormalities may be the source of the increased susceptibility to infection seen in some people with autism.

Diet is a controversial aspect of autism. The greatest attention has been given to gluten- and casein-free diets; anecdotal information suggests that these diets help some children with autism. [47] Test findings suggest that low-functioning children with autism may have impairment in the metabolism of phenolic amines. [48] Therefore, symptoms of autistic disorder are possibly aggravated by the consumption of dairy products, chocolates, corn, sugar, apples, and bananas; however, no large population studies have confirmed this.

Oxidative stress may play a role in the pathogenesis and the pathophysiology of autism. [49] Compared with normal children, children with autism have decrements in the following: [49]

  • Plasma levels of cysteine, glutathione, and methionine

  • The ratio of S -adenosyl-L-methionine (SAM) to S -adenosyl-L-homocysteine (SAH)

  • The ratio of reduced to oxidized glutathione

Some children with autism display hyperlacticacidemia [50] as well as evidence of mitochondrial disorders [50] including carnitine deficiency. [51] These abnormalities may reflect disturbed neuronal energy metabolism.


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