SLC6A4 and autism: In addition, five subjects (2%) of the 248 ASD-affected patients were heterozygous for the SLC6A4 base change c.167G > C, encoding p.Gly56Ala (Additional file 2: Table S2), which did not differ significantly from the frequency of 2.3% in the control populations, and has already been associated with autism and rigid-compulsive behaviors [28].