A genome scan on a sample of families affected with schizophrenia, led to the discovery of a strong linkage signal on chromosome 6q23. This signal was further explored by typing single nucleotide polymorphisms (SNPs) in the vicinity of the linkage peak. A strong genetic association with schizophrenia for single SNPs and haplotypes in a genomic region of high linkage disequilibrium was identified. Within this region the association signal was strongest in the Abelson Helper Integration Site 1 (AHI1) gene and an adjacent, non-annotated primate-specific mRNA.
The findings of the invention indicate that the presence of specific SNP alleles and haplotypes in the RGS2 gene can be used to predict susceptibility and/or resistance to EPS and may thus be helpful in designing a treatment regimen that includes typical antipsychotics.