Comorbid conditions and ASD
Comorbid conditions are common in children and families with ASD. Parents of affected children have increased rates of stress, anxiety and depression [21]. Comorbid behavioural and developmental disorders in people diagnosed with ASD include intellectual delays, inattention, attention-deficit hyperactivity disorder, aggression and disruption, depression or anxiety, sleep disruption or sensory differences [22,23]. Other comorbidities include gastroesophageal reflux, flood selectivity and neurological disorders, such as tics, seizures or migraine [24]. Many of these conditions have been linked to the dysregulation of serotonergic systems [25-34]. Abnormalities in serotonergic function have been linked with ASD since Schain and Freedman reported hyperserotonemia in 1961 [35]. This observation has been confirmed in subsequent studies where in 25 to 33% of individuals diagnosed with ASD, whole blood serotonin levels were found to be elevated [36]. Furthermore, family members of children diagnosed with ASD with hyperserotonemia also exhibit raised blood serotonin levels [37].