Objective: Autism/autistic disorder (MIM number 209850) is a complex, largely genetic psychiatric disorder. The authors recently mapped a susceptibility locus for autism to chromosome region 2q24-q33 (MIM number 606053). In the present study, genes across the 2q24-q33 interval were analyzed to identify an autism susceptibility gene in this region.
Method: Mutation screening of positional candidate genes was performed in two stages. The first stage involved identifying, in unrelated subjects showing linkage to 2q24-q33, genetic variants in exons and flanking sequence within candidate genes and comparing the frequency of the variants between autistic and unrelated nonautistic subjects. Two single nucleotide polymorphisms (SNPs) that showed evidence for divergent distribution between autistic and nonautistic subjects were identified, both within SLC25A12, a gene encoding the mitochondrial aspartate/glutamate carrier (AGC1). In the second stage, the two SNPs in SLC25A12 were further genotyped in 411 autistic families, and linkage and association tests were carried out in the 197 informative families.
Results: Linkage and association were observed between autistic disorder and the two SNPs, rs2056202 and rs2292813, found in SLC25A12. Using either a single affected subject per family or all affected subjects, evidence for excess transmission was found by the Transmission Disequilibrium Test for rs2056202, rs2292813, and a two-locus G*G haplotype. Similar results were observed using TRANSMIT for the analyses. Evidence for linkage was supported by linkage analysis with the two SNPs, with a maximal multipoint nonparametric linkage score of 1.57 and a maximal multipoint heterogeneity lod score of 2.11. Genotype relative risk could be estimated to be between 2.4 and 4.8 for persons homozygous at these loci.
Conclusions: A strong association of autism with SNPs within the SLC25A12 gene was demonstrated. Further studies are needed to confirm this association and to decipher any potential etiological role of AGC1 in autism.