Amino acids are the chemical building blocks of key neurotransmitters that act on the brain to influence mood and behaviour. For this reason, the proper balance of these nutrients is essential for healthy emotional and cognitive development in children.
Tryptophan is an amino acid the body uses to produce serotonin, a powerful regulator of mood and behaviour. Some researchers believe that dysregulation of serotonin function may profoundly influence the severity of symptoms in some individuals with autism, and may be closely connected with related immune system dysfunction. In one study, when researchers induced a clinical depletion of tryptophan in twenty autistic adults not taking pharmaceutical drugs, they observed a significant increase in behaviours such as pacing, rocking, self-hitting, as well as more anxiety and less happiness. In general, the autistic patients with highest baseline plasma levels of tryptophan showed the most severe responses after a tryptophan depletion was induced.
A recent case-control study by Belgian researchers found that plasma concentrations of tryptophan were significantly lower in a group of teenagers with autism than in age-matched controls. Investigators conjectured that this imbalance may be an important factor in the pathophysiology of autism.
High levels of excitatory neurotransmitter amino acids, such as glutamic acid and aspartic acid, have been observed in younger children with autism. These imbalances may be related to metabolic dysfunction involving Vitamin B6. This study also reported higher levels of the inhibitory amino acid taurine in the children, which may occur as their bodies try to “compensate” for excess levels of the excitatory neurotransmitters.
Levels of amino acids secreted in urine can also provide important clues about dietary and digestive factors influencing autism. A study published in JAMA reported that children with severe developmental disorders involving both autism and psychosis may have excessive levels of phenylalanine, a condition known as phenylketonuria (PKU), which can lead to brain damage and seizures.
Jon Pangborn, PhD, a leading expert on aminoacidopathies, observes that 24-hour urinary amino acid analysis in children with developmental disorders often reveals imbalances signifying maldigestion-such as elevated dietary peptides and their markers (anserine, carnosine, 1-methylhistidine, and beta-alanine). In addition, there may be deficiencies of essential and semi-essential amino acids, especially the sulfur amino acids methionine, cystine, and taurine, suggesting chronic digestive dysfunction, which can lead to dysbiosis (imbalanced microbial flora) over time.
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- McDougle CJ, Naylor ST, Cohen DJ, Aghajanian GK, Heninger GR, Price LH. Effects of tryptophan depletion in drug-free adults with autistic disorder. Arch Gen Psychiatry 1996;53(11):993-1000.
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- Lowe TL, Tanaka K, Seashore MR, Young JG, Cohen DJ. Detection of phenylketonuria in autistic and psychotic children. JAMA 1980;243(2):126-8.
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