In the present study we investigated genetic variants associated with bipolar disorder in a homogenous Norwegian sample, and potential genetic overlap with schizophrenia, using the Affymetrix 6.0 array.
We carried out a genome-wide association study (GWAS) by genotyping 620 390 single-nucleotide polymorphisms (SNPs) in a case-control sample of Norwegian origin (the TOP study) including bipolar disorder (n=194), healthy controls (n=336) and schizophrenia (n=230), followed by replication and combined analysis in a genetically concordant Icelandic sample of bipolar disorder (n=435), and healthy controls (n=10,258).
We selected 1000 markers with the lowest P values in the TOP discovery GWAS and tested these (or their surrogates) for association in the Icelandic replication sample. Polymorphisms on 35 loci were confirmed associated with bipolar disorder (nominal P value