MAOA and sudden infant death syndrome: Given that MAOA plays an important role in the inactivation process of serotonin and noradrenalin in the human brainstem, the findings of the higher frequency in male infants with SIDS carrying low-expression alleles of the MAOA promoter are, thus, supported by theoretical evidence, with the correlation between 5-HT level and SIDS being of great potential for further investigation.