SLC6A4 and psychiatric disorder: At the same time ASD is associated with multiple polymorphisms in the SLC6A4 gene with individuals heterozygous for the Gly56Ala plus 5-HTTLPR L/L promoter variants [73], and other studies into SLC6A4 and other psychiatric disorders suggests that haplotypes (multiple alleles) that include the 5-HTTLPR variants may contribute to this disorder [122,123].