Increased Glutamate and Homocysteine and Decreased Glutamine Levels in Autism: A Review and Strategies for Future Studies of Amino Acids in Autism

Table 2

The level of amino acids in patients with autism in comparison to healthy controls.

Amino acid	Status
Leucine	Decreased in CSF [21]; Decreased in plasma [8, 16, 17, 21]
Lysine	Increased in plasma [8, 10, 16]; No difference in plasma [17]
Tryptophan	Decreased in plasma [16, 17]
Taurine	Decreased in plasma [16]; Increased in plasma [15, 22]
Homocysteine	Increased in serum [16, 23]; Increased total homocysteine (tHcy) in serum [24]; Decreased plasma levels of homocysteine [25]; Increased level in urine [26]
Citrulline	Decreased in plasma [17]
Alanine	No difference in plasma [17]; Increased in plasma [10]
Glycine	No difference in plasma [17]
Valine	Decreased in plasma [8, 16]; No difference in plasma [17]
Aspartic acid	Decreased platelet levels [27]
GABA	Decreased platelet levels [27]
Arginine	No difference in plasma [17]
Isoleucine	Decreased [21]
Threonine	Decreased in plasma [17]
Serine	Decreased in plasma [17]
Proline	No difference in plasma [17]
Asparagine	Decreased in plasma [15, 17]; Increased in plasma [10]
Aspartic acid	No difference in plasma [17]
Methionine	Increased in plasma [8]; Decreased [21]
Glycine	No difference in serum level [19]
D-serine	No difference in serum level [19]
L-serine	No difference in serum level [19]
Glutamic acid	Increased in plasma [10, 16, 17]; Decreased platelet levels [27]
Glutamate	Increased level in plasma [9, 10, 15, 19, 28]; Increased in some regions of brain [20]
Aspartate	Increased in plasma [22]
Phenylalanine	Decreased in plasma [8, 17]; Increased in plasma [10]
Glutamine	Decreased in plasma [9, 10, 15–17]; No difference in serum level [19]; Decreased platelet levels [27]
Lysine	Increased in plasma [10]
Tyrosine	Decreased in plasma [16, 17]; Increased in plasma [10]