“…The underlying mechanism for hyperserotonemia is investigated through genetic studies, mainly restricting to key regulators of 5-HT homeostasis such as tryptophan hydroxylase (TPH), 5-HT transporter (SERT), 5-HT 2A receptor and monoamine oxidases (MAO). Association studies using genes encoding proteins that regulate 5-HT levels and its activity are examined to identify genetic variants conferring susceptibility to ASD (Cohen et al, 2011;Conroy et al, 2004;Cook et al, 1997;Hranilovic et al, 2010;Kim et al, 2002;Yang et al, 2012), but inconsistent results on association made it difficult to accurately nail down an isolated gene or a group of genetic markers (Coutinho et al, 2004;Guhathakurta et al, 2006Guhathakurta et al, , 2008Jaiswal et al, 2015;Tassone et al, 2011;Verma et al, 2014). In addition to genetic analyses, researchers have used theoretical models to investigate the hyperserotonemia in autism (Anderson et al, 1987a;Janusonis, 2008).…”