This is the first South African study of autistic individuals of different ethnic backgrounds that shows significant differences in allele and genotype frequencies of 5-HTTLPR.
We report a significant main effect of the HTR5A gene in autism (P = 0.0088), and a significant three-locus model comprising a synergistic interaction between the ITGB3 and SLC6A4 genes with an additive effect of HTR5A (P < 0.0010).