Novel genetic variants of the Glutamate Receptor, Metabotropic 8 (GRM8) gene are described. Various genotypes, haplotypes, and haplotype pairs that exist in the general United States population are disclosed for the GRM8 gene. Compositions and methods for haplotyping and/or genotyping the GRM8 gene in an individual are also disclosed. Polynucleotides defined by the haplotypes disclosed herein are also described.
