Pharmacogenetic Analysis of Dopamine and Glutamate Receptor Gene Polymorphisms and Clinical Response to Clozapine in Patients wtih Schizophrenia

• Main Author: Hwang, Rudi Wei-ru
• Other Authors: Kennedy, James L.
• Language: en_ca
• Published: 2014
• Subjects: pharmacogenetics; schizophrenia; 0347
• Online Access: http://hdl.handle.net/1807/44116

Interpatient variability in clinical response to antipsychotics (AP) is observed in the treatment of schizophrenia (SCZ) with evidence to support a genetic basis for this phenomenon. Dysfunction in the dopaminergic (DA) system as well as the glutamatergic (GLU) system have both been implicated in the formation of SCZ symptoms. Therefore, we explored the role of DA and GLU receptor variation on clinical response to CLZ, an AP of last resort. We focused on DA receptor genes DRD3, DRD4, and DRD5 having already previously published on DRD1 and DRD2 in this sample. N-methyl-D-aspartate receptor (NMDAR) subunit gene variants and epistatic effects between and among these variants and DA receptor gene variants were also studied. For DRD3, we extended a statistically significant meta-analysis on single nucleotide polymorphism (SNP) rs6280 (Ser9Gly) previously performed by Jonsson et al. (2003). We observed a consistent trend for the serine allele and poor CLZ response (six of seven studies with the same direction of effect). Eight other tagged DRD3 SNPs were also tested with two identified for future replication. For DRD4, associations were observed between the 4-repeat allele of the exon III variable number tandem repeat (VNTR) polymorphism and better CLZ response in Caucasians with a non-significant but same direction of effect in African-Americans; the 142/140-base pair (bp) genotype of the intron 1 guanine mononucleotide repeat ((G)n) polymorphism with poor CLZ response in the whole sample; and the 1-copy allele of the 5’-flanking region 120-bp tandem repeat polymorphism in African-Americans. Three other tagged SNPs across DRD4 and five across DRD5 were negative. Our investigation of GLU receptor gene variants focused on NMDAR subunit genes GRIN1, GRIN2A, and GRIN2B with negative findings. Examining gene-gene epistatic effects among and between NMDAR subunit and DA receptor gene polymorphisms identified several interactions with the strongest result being between the DRD1 rs686 G carrier/DRD3 Ser9Gly G non-carrier group with good response. Overall, our results suggest possible minor roles for DA receptor gene variants on CLZ response. Integrating this data with exciting new advances in technologies and bioinformatics will surely bring us closer to personalized medicine in psychiatry.