Metabolomic changes in children with autism

Table 1 The changes observed in each amino acid metabolic pathway in individuals with autism spectrum disorder, along with relevant studies and their methods

Ref.	Study methods	Amino acid pathway	Changes in ASD
Boccuto et al[40]	Blood or CSF sample analysis	phenylalanine and glutamate	Elevated phenylalanine and glutamate levels
Ormstad et al[41]	Metabolomic profiling	phenylalanine and glutamate	Decreased glutathione and creatine levels
Almulla et al[42]	Peripheral blood analysis	Tryptophan pathway	Disrupted tryptophan metabolism
Higazi et al[56]	Genetic analysis of MAOA, HAAO and AADAT genes using real-time RT-qPCR.	tryptophan pathway	significant decrease in the expression of the selected genes within ASD children relative to children with learning disabilities and healthy controls
Naushad et al[66]	Genetic analysis	Tryptophan pathway	Lower serotonin synthesis
Naushad et al[66]	Enzyme activity measurement	Phenylalanine and tyrosine metabolism	Reduced tyrosine synthesis
Arum et al[71]	Dietary intake assessment	Phenylalanine and tyrosine metabolism	Abnormal phenylalanine-to-tyrosine ratio
Geier et al[84]	Peripheral blood analysis	Methionine and sulfur metabolism	reduced levels of serum glutathione, cysteine, methionine, cystathionine, and homocysteine in pre-pubertal children
Suh et al[85]	Genetic analysis	Methionine and sulfur metabolism	Reduced SAM levels
Guo et al[86]	Meta-analysis of metabolomic profiling	Methionine and sulfur metabolism	Impaired methylation capacity
Haghiri et al[89]	Genetic analysis	Methionine metabolism	mutations of methionine synthase in children with ASD

AADAT gene: Aminoadipate Aminotransferase gene; ASD: Autism spectrum disorder; HAAO gene: 3-Hydroxyanthranilate 3,4-dioxygenase is a monomeric cytosolic protein gene; MAOA gene: monoamine oxidase A gene; SAM: S-adenosylmethionine.