Furthermore, after conducting with the quantitative scores in the Autism Diagnostic Interview-Revised, there were associations between restricted, repetitive, and stereotyped patterns of behavior (preoccupation with parts of objects or nonfunctional elements of materials) in ASD and SNPs in TPH2.
TPH2 alleles and haplotypes are not significantly associated in our sample with autism (rs4570625: TDT P = 0.27, and FBAT P = 0.35; rs4565946: TDT P = 0.45, and FBAT P = 0.55; haplotype P = 0.84), with any endophenotype, or with the presence/absence of prominent repetitive and stereotyped behaviors (motor stereotypies: P = 0.81 and 0.84, verbal stereotypies: P = 0.38 and 0.73 for rs4570625 and rs4565946, respectively).
Thus, it appears unlikely that the TPH1 and TPH2 genes play a significant role in the susceptibility to autism or to autism endophenotypes including sOCB and SSB.