GRK3 is a gene on chromosome 22 that has been linked in some studies (and not others) to bipolar disorder.
In 2003, GRK3 alleles with a variant dubbed "P-5", located at the -382 position relative to the transcriptional start site, were found at a frequency of 0.007 (i.e. 7 out of 1000) in the general population, and at a ~4 fold higher frequency (0.028) in patients with bipolar disorder.[PMID 12808434]
The P-5 variant is quite rare, and lacks a dbSNP rs# at this time. For reference purposes, the sequence surrounding the variant is shown below, with R at position 195 designating the SNP. The common nucleotide is (G), and the rare variant is (A) at this SNP:
1 gcctccccat aaccccttgg gttgtggacg tctggcccag ggcttctctg ggtgagcggg 61 gcgggcatca gagcgcgtgg aacctggggc gggaggtcgg ggcagtgaag gaggaggaga 121 aggaggaggc ggagaccgag ggggagggag gggaggagga agaggaggag gagtccctcg 181 tggccacccc gaggRgaggg cgaccgtaga gacttggtcg ggaggcgccg gcccagcgag 241 gccgctggga ctgtgcactg aggggcgctg accgttggac gcgcgctccc cgcagaccct 301 cgctgaagga gcagggggcg gcgcgcgtgc gcggggcgcc gggcggcgcg cgagggggcg 361 gagcggggag gcgtgctgcg accccggccg gctacagcct gcggcgcgc
A more recent study (by the same scientists and therefore company selling a test) identified two bipolar disease-associated haplotypes in 181 Caucasian families. These two haplotypes have a combined frequency of 1 in 10, and are defined by four SNPs also located upstream of the GRK3 promoter region. The odds ratios for the haplotypes was reported as 2.50 and 2.36, p=0.0009 and 0.05 and still significant after correction for multiple testing. And once again, the authors do not cite any dbSNP rs#'s, and the supplementary information said to be online is not.[PMID 18075471] See also:10.1126/science.319.5861.274