Psychosis and relapse in bipolar disorder are related to GRM3, DAOA, and GRIN2B genotype.
OBJECTIVE
Dysfunction in glutamate signalling is thought to play a role in the pathophysiology of bipolar disorder (BD). There is evidence of associations between single nucleotide polymorphisms (SNPs) in GRM3, GRIN2B, and DAOA genes and the diagnosis of BD. In this pilot study, we investigated the frequency of SNP variants in these 3 genes within South African population groups, and assessed interactions between genes and phenotypes of BD disease severity.


METHODS
Multiplex SNaPshotTM PCR was used to genotype 191 case and 188 control samples. Cases comprised of 191 individuals in a South African cohort of mixed ancestry and Caucasians, with BD Type 1. Phenotypes of BD disease severity were: age of onset, number of illness episodes, number of hospitalisations for depression or mania and history of psychotic symptoms.


RESULTS
There were no significant difference in SNP allele frequencies between cases and controls. In the case-only analysis, the GRM3 rs6465084 heterozygote was associated with a 4-fold increased risk of lifetime history of psychotic symptoms, and the specific variants within the gene pair, DAOA and GRIN2B, had a significant interaction with the number of hospitalisations for mania, with lowest admission rates associated with both pairs of ancestral alleles.


CONCLUSIONS
In BD, variations in glutamatergic genes may influence phenotypes related to the severity of illness. Speculatively, newly derived genes associated with various evolutionary advantages, may also increase the risk for more severe BD. These preliminary findings deserve validation in a larger cohort.
Dalvie
S
S
Division of Human Genetics, MRC/UCT Human Genetics Research Unit, Faculty of Health Sciences, University of Cape Town Medical School, Observatory, Cape Town, South Africa.
Horn
N
N
Nossek
C
C
van der Merwe
L
L
Stein
D J
DJ
Ramesar
R
R
D001714:Bipolar Disorder / Q000235:genetics*; D002352:Carrier Proteins / Q000235:genetics*; D016022:Case-Control Studies; D015331:Cohort Studies; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D010641:Phenotype; D010865:Pilot Projects; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011618:Psychotic Disorders / Q000235:genetics*; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics*; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics*; D012008:Recurrence; D012720:Severity of Illness Index; D013019:South Africa
D002352:Carrier Proteins; C475071:DAOA protein, human; D047908:Intracellular Signaling Peptides and Proteins; C121001:NR2B NMDA receptor; D018094:Receptors, Metabotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; C102718:metabotropic glutamate receptor 3