SLC6A4 and autism: In a second vein, specific haplotypes related to the polymorphism of the SLC6A4 serotonin transporter (SERT) gene correlate with hyperfunctioning of serotonin transporter SERT in brain, in circulating platelets, and in enterocytes (17), further indicating interconnections between genetic risk factors for autism and gastrointestinal abnormalities.