SLC6A4 and autism: Putative and known candidates for susceptibility to autism are categorized to differentiation of neurons (e.g. DISC1, MET, PTEN, and ITGB3), neuronal cell adhesion (e.g. NRXN1, NLGN3, and NLGN4X), transmission of nervous system (e.g. OXTR, SLC6A4, GABRB3, and SHANK3), and regulation of neuronal activity (e.g. FMR1, MECP2, and UBE3A).