Based on these lines of evidence, the transmission/disequilibrium test (TDT) was used to assess transmission disequilibrium between autism and haplotypes of three polymorphisms, including the promoter -1438 G/A single nucleotide polymorphism (SNP) in perfect linkage disequilibrium with the 102 T/C SNP in previous studies, a newly identified SNP in intron 1 near exon 2, and the SNP responsible for the His452Tyr amino acid change in exon 3.