Early Infant Exposure to Excess Multivitamin: A Risk Factor for Autism?

Figure 1

The synthesis and degradation of serotonin and catecholamines. Oxidative deamination and methylation are two key mechanisms for inactivating monoamine neurotransmitters. Note that without labile methyl groups, methylation-mediated degradation of serotonin and catecholamines cannot take place, even though the methyltransferases involved are normal. 1, monoamine oxidase; 2, aldehyde dehydrogenase; 3, aldehyde reductase; 4, acetylserotonin O-methyltransferase; 5, catechol-O-methyltransferase. AADC: aromatic L-amino acid decarboxylase; DHMA: 3,4-dihydroxymandelic acid; DHPG: 3,4-dihydroxyphenylglycol; DHR: dihydropteridine reductase; DOPAC: 3,4-dihydroxyphenylacetic acid; GTP: guanosine triphosphate; MHPG: 3-methoxy-4-hydroxyphenylglycol; PAH: phenylalanine hydroxylase; PNMT: phenylethanolamine N-methyltransferase; PPAT: phenylalanine(histidine):pyruvate aminotransferase; SNAT: serotonin N-acetyltransferase; TH, tyrosine-3-hydroxylase; TPH, tryptophan-5-hydroxylase; VMA: vanillylmandelic acid.