Synergistic association of PI4KA and GRM3 genetic polymorphisms with poor antipsychotic response in south Indian schizophrenia patients with low severity of illness

Literature indicates key role of glutamatergic pathway genes in antipsychotic response among schizophrenia patients. However, molecular basis of their underlying role in antipsychotic response remained unexplained. Thus, to unravel their molecular underpinnings, we sought to investigate interactions amongst GRM3 , SLC1A1 , SLC1A2 , SLC1A3 , SLC1A4 gene polymorphisms with drug response in south Indian schizophrenia patients. We genotyped 48 SNPs from these genes in 423 schizophrenia patients stratified into low and high severity of illness groups. The SNPs and haplotypic combinations of associated SNPs were examined for their association with antipsychotic response. Multifactor‐dimensionality‐reduction was further used to explore gene‐gene interaction among these SNPs and 53 SNPs from previously studied genes ( BDNF , RGS4 , SLC6A3 , PI4KA , and PIP4K2A ). Single SNP and haplotype analyses revealed no significant association with drug response irrespective of severity of illness. Gene‐gene interaction analyses yielded promising leads, including an observed synergistic effect between PI4KA _rs165854 and GRM3 _rs1468412 polymorphisms and incomplete antipsychotic response in schizophrenia patients with low severity of illness (OR = 12.4; 95%CI = 3.69–41.69). Further, this interaction was also observed in atypical monotherapy (n = 355) and risperidone (n = 260) treatment subgroups (OR = 11.21; 95%CI = 3.30–38.12 and OR = 13.5; 95%CI = 3.03–121.61 respectively). PI4KA is known to be involved in the biosynthesis of phosphatidylinositol‐4, 5‐bisphosphate which regulates exocytotic fusion of synaptic vesicles (glutamate, dopamine) with the plasma membrane and regulates duration of signal transduction of GPCRs. Whereas GRM3 regulates glutamate and dopamine transmission. Present findings indicate that PI4KA and GRM3 polymorphisms have potential to jointly modulate antipsychotic response. These results warrant additional replication studies to shed further light on these interactions. © 2014 Wiley Periodicals, Inc.