Table 1.

Abnormal metabolism associated with autism spectrum disorder from metabolomic studies in urine samples

Ref and Subjects	Age (years)	Method	Categories of Metabo- lite/ Metabolic pathway involvement	Changes in metabolites compared to typical children		Interpretation
				Increase	Decrease
Gevi et al. 2020
40 ASD compared with 40 typical children	3-8	Untargeted approach using UHPLC-MS	Neurotransmitter	Glutamate	GABA	There are abnormalities of neurotransmitters and metabolites related to microbiota-brain-gut axis in the urine of children with ASD.
					Pyridoxal phosphate
			Neurotransmitter/microbiota-brain-gut axis	4-Cresol	Noradrenaline
				Ascorbate	Adrenaline
				Homovanillic acid	MHPG Vanillylmandelic acid
Liang, Ke et al. 2020
40 ASD compared with 40 typical children	3-12	Untargeted approach using UHPLC-QTOF/MS	Nicotinate and nicotinamide metabolism	Nicotinamide		There are abnormalities of nicotinamide, phosphorylcholine, amino acid, acetyl-CoA synthase, lysine, nucleosides, neurotransmitter, naphthalene metabolites, sialic acid, purine, and lipid metabolism in urine of children with ASD.
			Phosphorylcholine metabolism	Phosphorylcholine
			Amino acid metabolism	Glycylglutamate Alanylthreonine Threonylaspartate Histidylproline Lysylproline Valylmethionine Methionylglutamine	Prolylserine
			Acetyl-CoA synthase	Acetylcarnitine
			Tryptophan kynurenine pathway	D-neopterin 7,8-Dihydroneopterin Anthranilic acid
			Catabolism of lysine	5-Aminopentanoic acid
			Modified nucleosides	1-Methyladenosine 3’-O-Methylinosine
			Neurotransmitter	N-Acetylaspartylglutamate
			Naphthalene metabolites	1-Naphthol
			Sialic acid pathway	N-Acetylneuraminic acid
			Purine metabolism	Deoxyinosine
			Lipid metabolism	Behenic acid
			Other	Bethanechol cation S-Methyl-5’-thioadenosine
Liang, Xiao et al. 2020
22 ASD compared with 22 non-ASD siblings	3-9	Untargeted approach using 1H-NMR	Cysteine metabolism	Taurine		There are abnormalities of cysteine, methionine, oxidative stress, sulfur, and tryptophan-serotonin-melatonin metabolic pathway in urine of children with ASD.
			Methionine cycle	Taurine
			Reactive oxidative stress	Taurine
			Sulfur metabolism	Taurine
			Tryptophan-serotonin-melatonin pathway	Tryptophan Serotonin	Melatonin
			Others	Creatine	Butyrate Citrate Lactate Pantothenate Trigonelline
Mussap et al. 2020
31 ASD compared with 26 typical children	2-11	Untargeted approach using GC-MS	Oxidative stress	Cystine	7-Methylxanthine Uric acid	There are differences of metabolite levels resulting from oxidative stress, mitochondrial dysfunction, sugar metabolism, gut dysbiosis, and diet in urine of children with ASD compared to those of typically developing children.
			Mitochondrial dysfunction	Lactic acid
			Sugar metabolism		Scylloinositol
			Gut dysbiosis	Quinic acid Hippuric acid Tryptophan Indole-3-acetic acid Allyl thioacetic acid Leucine
			Diet	1-Methylhistidine
			Others		Aminomalonic acid
Olesova et al. 2020
24 ASD compared with 13 typical children	6-10	Targeted approach using UHPLC-QqQ-MS/MS	Reactive oxidative stress	Methylguanidine N-acetylarginine		There are abnormalities of reactive oxidative stress and gut bacteria metabolism in the urine of children with ASD.
			Gut bacteria metabolism	Indoxyl sulphate Indole-3-acetic acid
Liu et al. 2019
57 ASD compared with 81 typical children	2-12	Targeted approach using LC-MS/MS	Ornithine (Urea) cycle Ornithine (Urea) cycle	Ornithine-to-Citrulline ratio	Proline	There are abnormalities of ornithine (urea) cycle, methionine, lysine, reactive oxidative stress, tryptophan-serotonin metabolism in urine of children with ASD.
				Arginine-to-Ornithine	Citrulline
				Arginine 4-Hydroxyproline	Aspartic acid
			Methionine cycle	Methionine sulfoxide	Homocysteine 5-Aminovaleric acid a-Aminoadipic acid Ethanolamine
			Lysine metabolism		Lysine
			Reactive oxidative stress		Anserine Carnosine
			Tryptophan-Serotonin metabolism	5-Hydroxytryptamine
			Others	2-Aminoisobutyric acid
Chen et al. 2019
156 ASD compared with 64 typical children	NA	Untargeted approach using GC/MS	Phenylalanine metabolism	Phenylactic acid		There are abnormalities of phenylalanine, TCA cycle, bone metabolism, mammalian-microbial co-metabolism in urine of ASD.
			TCA cycle		Aconitic acid Carboxycitric acid
			Bone metabolism		Phosphoric acid
			Mammalian-microbial co-metabolism		3-Oxoglutaric acid Carboxycitric acid
			Others	3-Hydroxy-3-methylglutaric	Fumaric
				Creatinine	N-Acetylcysteine
				Oxalic	Malonic
				Pyruvic	Tricarballylic
				4-cresol	Glycolic
				2-hydroxybutyric	Malic Tartaric 3-Hydroxyglutaric 2-Oxoglutaric
Xiong et al. 2019
51 ASD compared with 51 typical children	3-7	Untargeted approach using HPLC-QTOF-MS	Adenosine-Adenine pathway	Adenine		There are abnormalities of adenosine-adenine pathway, methylation regulation of retinoic acid-RORA pathway, and arginine metabolism, predominantly in female patient with ASD.
			Methylation regulation of retinoic acid-RORA pathway	2-Methylguanosine 7alpha-Hydroxytestololactone
			Arginine metabolism	Creatinine	Creatine
Bitar et al. 2018
40 ASD compared with 40 typical children	NA	Untargeted approach using 1H-NMR and LC-MS	Glycine, serine and threonine metabolism	Phosphoserine	Threonine Creatine Serine	There are abnormalities in amino acids, nicotinic acid, TCA cycle, purine, vitamin, and fatty acid metabolism in urine of ASD.
			Phenylalanine metabolism		N-acetylphenylalanine Tyrosine Hydroxybenzoic acid
			Glutamate, Arginine and Proline metabolism	Glutamic acid	Creatine Hydroxyproline
			Histidine metabolism	Glutamic acid	Urocanic acid
			Cysteine and Methionine metabolism	Phosphoserine	Cysteic acid Serine
			Propanoate metabolism		2-hydroxybutyric acid
			Nicotinate and nicotinamide metabolism	Nicotinamide ribotide Trigonelline
			TCA cycle		Citric acid
			Purine metabolism	5-amino-imidazole-4-carboxamide	Guanine
			Vitamin B6 metabolism	Riboflavin
			Fatty acid oxidation		N-amidino aspartic acid Acetylcarnitine
			Others	Glycerol-3-phosphate Cholic acid	Methyl acetoacetic acid
Lussu et al. 2017
21 ASD compared with 21 non-ASD siblings	4-16	Untargeted approach using 1H-NMR	Neurotransmitter	Glycine	Glutamate	There are abnormalities of neurotransmitter, tryptophan-serotonin, mammalian-microbial co-metabolism, oxidative stress metabolism in urine of ASD.
			Tryptophan-serotonin metabolism	Tryptophan
			Mammalian-microbial co-metabolism	Hippurate
			Oxidative stress		Taurine Lactate
			Others	Creatine D-threitol	Valine Betaine Creatinine
Xiong et al. 2016
62 ASD compared with 62 typical children	1.5-7	Untargeted approach using GC/MS	Mammalian-microbial co-metabolism	3-(3-hydroxyphenyl)-3-Hydroxypropionic acid 3-Hydroxyphenylacetic acid 3-Hydroxyhippuric acid		There are abnormalities in mammalian-microbial co-metabolism in urine of ASD.
Gevi et al. 2016
30 ASD compared with 30 typical children	2-7	Untargeted approach using LC-MS	Purine metabolism	Inosine Hypoxanthine Xanthosine	Adenosine diphosphate	There are abnormalities of nucleic acid (purine, pyrimidine), amino acid (tryptophan), vitamins (B1, B2, B6, and pantothenate), mammalian-microbial co-metabolism, glutathione, pentose phosphate pathway, benzoate degradation, and carbohydrate metabolism in urine of ASD.
			Pyrimidine metabolism	Uridine
			Tryptophan metabolism	Xanthurenic acid Quinolinic acid Tryptophan	Kynurenine
			Mammalian-microbial co-metabolism	Indolyl 3-acetic acid Indolyl lactate
			Disaccharide metabolism	Trehalose/sucrose	Cellobiose
			Other amino acid metabolism	Phenylalanine Histidine	Methionine
			Glutathione metabolism		Pyroglutamic acid
			Pentose Phosphate Pathway	6-phospho-D-gluconic acid Ribose
			Benzoate degradation	p-cresol	p-hydroxybenzoate
			Vit B1 metabolism	Thiamine
			Vit B2 metabolism	Riboflavin
			Vit B6 metabolism	4-pyriodic acid
			Pantothenate and CoA metabolism		Glucose-6-phosphate
			Glycolysis		Glucose-6-phosphate
Diémé et al. 2015
30 ASD compared with 32 typical children	NA	Untargeted approach using 1H-NMR, 1H-13C-NMR and LC-HRMS	Reactive oxidative stress	N-acetylarginine	Methylguanidine Guanidinosuccinic acid	There are abnormalities in reactive oxidative stress, tyrosine, pyrimidine, and mammalian-microbial co-metabolism in urine of ASD.
			Tyrosine metabolism	Dihydroxy-1H-indole glucuronide I
			Pyrimidine metabolism		Dihydrouracil
			Mammalian-microbial co-metabolism	Indoxyl Indoxyl sulfate Alpha-N-Phenylacetyl-L-glutamine p-cresol sulfate	Desaminotyrosine
			Others	N-Acetylasparagine Valine Glucuronic acid
Cozzolino et al. 2014
24 ASD compared with 21 typical children	6.9 +/−2.1	Untargeted approach using Solid-phase microextraction with GC/MS	Leucine metabolism	3-Methylbutanal (under acid conditions)		There are abnormalities in leucine, fatty acid, and degradation of carbohydrate metabolism in urine of ASD.
			Peroxidation of fatty acid	3-Methylbutanal (under acid conditions) 2-Methylbutanal (under acid conditions)
			Dietary degradation of carbohydrate		2-Methylmercaptofuran (under acid conditions) 2-Pentylfuran (under acid conditions)
			Others	3-Methylcyclopentanone (under acid conditions)	2-Heptanone (under alkaline conditions)
				Hexane (under acid conditions)	Ethanol (under acid conditions)
				2,3-Dimethylpyrazine (under alkaline conditions)	Dimethyl trisulfide (under acid conditions)
				2-Methylpyrazine (under alkaline conditions)	Methoxy-phenyloxime (under alkaline conditions)
				Isoxazole (under alkaline conditions)	3-Ethylpyridine (under alkaline conditions) Acetophenone (under alkaline conditions)
Noto et al. 2014
21 ASD compared with 21 non-ASD siblings	4-16	Untargeted approach using GC/MS	Mammalian-microbial co-metabolism	3-(3-Hydroxyphenyl)-3-hydroxypropanoic acid Glycolic acid 4-Hydroxyhippuric acid		There are abnormalities of TCA cycle, Tryptophan, Glutathione, oxidative cleavage of N-acetylglucosamine, Tyrosine, pentose phosphate pathway, and mammalian-microbial co-metabolism in urine of ASD.
			TCA cycle	Aconitic acid
			Tryptophan metabolism	Tryptophan
			Glutathione metabolism	Pyroglutamic acid
			Oxidative cleavage of N-acetylglucosamine	Erythronic acid
			Tyrosine pathway	Phenylalanine Tyrosine 4-Hydroxyphenylacetic acid Homovanillic acid
			Pentose Phosphate Pathway	Ribose Arabinofuranose Threitol Polyols arabitol Xylitol
			From dietary sources		Fructose 1,2,3-Butanetriol Propylene glycol
Mavel et al. 2013
30 ASD compared with 28 typical children	6-14	Targeted approach using 1H-NMR	Organic acid	Succinic acid		There are abnormalities of organic acid and amino acid metabolism in urine of ASD.
			Amino acid	Glycine	Creatine
				β-alanine Taurine	3-methylhistidine
Emond et al. 2013
26 ASD compared with 24 typical children	6-14	Untargeted approach using GC/MS	Mammalian-microbial co-metabolism		1H-indole-3-acetate Hippurate 3-hydroxyhippurate	There are abnormalities of organic acid, fatty acid, phenols, and mammalian-microbial co-metabolism in urine of ASD.
			Organic acid	Succinate Glycolate
			Fatty acid		Palmitate Stearate 3-methyladipate
			Phenols		p-Hydroxy mandelate 3-hydroxyphenylacetate
Ming et al. 2012
48 ASD compared with 53 typical children	6-14	Untargeted approach combined using UPLC-MS/MS and GC/MS	Histidine catabolism	Trans-Urocanate		There are abnormalities of amino acid (Histidine, Lysine, Tryptophan, Leucine), reactive oxidative stress, and mammalian-microbial co-metabolism in urine of ASD.
			Lysine and tryptophan catabolism	Glutaroylcarnitine
			Leucine catabolism	3-Methylglutaroylcarnitine
			Mammalian-microbial co-metabolism	2-(4-Hydroxyphenyl) propionate	3-(3-Hydroxyphenyl) propionate
				Taurocholenate sulfate	5-Amino-valerate
			Reactive oxidative stress		Carnosine Urate
			Amino acid and gamma-glutaryl amino acids		Glycine Serine Threonine Alanine β-alanine Histidine Taurine N-acetylglycine Gamma-glutamylleucine Gamma-glutamyltyrosine Gamma-glutamylthreonine
Yap et al. 2010
39 ASD compared with 28 non-ASD siblings 34 typical children	3-9	Untargeted approach using 1H-NMR	Nicotinic acid metabolism	N-methyl-2-pyridone-5-carboxamide N-methyl nicotinic acid N-methyl nicotinamide		There are abnormalities of nicotinic acid, amino acid, mammalian microbial co-metabolism in urine of ASD
			Amino acid metabolism	Taurine N-acetyl glycoprotein fragment Succinate	Glutamate
			Mammalian microbial co-metabolites	Dimethylamine	Hippurate Phenylacetylglutamine
Nadal-Desbarats et al. 2014
30 ASD compared with 28 typical children	6-14	Targeted approach using combined 1H-NMR and 2D 1H-13C HSQC NMR	TCA cycle	Succinate		There are abnormalities of TCA cycle and glutamate metabolism in urine of ASD.
			Glutamate metabolism		Glutamate
			Others		3-methylhistidine

ASD autism spectrum disorder, TCA tricarboxylic acid cycle, UPLC-MS/MS ultra-performance liquid chromatography—tandem mass spectrometer, UHPLC-MS ultra-high-performance liquid chromatography-mass spectrometry, UHPLC-QTOF/MS ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry, UHPLC-QqQ-MS/MS ultra-high-performance liquid chromatography-tandem triple quadrupole-mass spectrometry, LC–MS liquid chromatography–mass spectrometry, LC–MS/MS liquid chromatography–tandem mass spectrometry, LC-HRMS liquid chromatography–high resolution mass spectrometry, GC–MS gas chromatography–mass spectrometry, ¹H-NMR hydrogen-1 nuclear magnetic resonance, ¹H-¹³C-NMR hydrogen-1 and carbon-13 nuclear magnetic resonance, 2D ¹H-¹³C HSQC NMR two-dimensional hydrogen-1 and carbon-13 heteronuclear single quantum correlation nuclear magnetic resonance; MS/MS: tandem mass spectrometry, HPLC-QTOF-MS high-performance liquid chromatography-quadrupole-time of flight mass spectrometry, GABA gamma-aminobutyric acid, RORA related orphan receptor alpha, NA data not available