MTNR1A and attention deficit-hyperactivity disorder: An altered mechanism of this hormone has been reported in ADHD patients, identifying a splice site mutation in ASMT and a nonsense mutation in MNTR1A (a gene encoding the melatonin receptor 1A, abundant in the prefrontal cortex and striatum) that nullifies the activity of the ASMT and AANAT enzymes and could explain the high comorbidity with sleep disorders reported in more than 25% of people with ADHD [50].