Publicly available databases, dbSNP (http://www.ncbi.nlm.nih.gov/SNP/) and HapMap (http://www.hapmap.org) were used to identify SNPs within the GRM8 gene. Genotyping was performed using Sequenom MassArray technology (http://www.sequenom.com, San Diego, CA, USA), homogenous MassEXTEND (hME). PCR primers, termination mixes, and multiplexing capabilities were determined with Sequenom MassARRAY Assay Designer software v3.1.2.2. Standard PCR procedures were used to amplify PCR products. All unincorporated nucleotides were deactivated with shrimp alkaline phosphatase. A primer extension reaction was then carried out with the mass extension primer and the appropriate termination mix (hME). The primer extension products were then cleaned with resin and spotted onto a silicon SpectroChip. The chip was scanned with a mass spectrometry workstation (Bruker) and the resulting genotype spectra were analyzed with the Sequenom SpectroTYPER software v3.4. All genotypic data were checked for Mendelian inheritance of marker alleles with the USERM13 (Boehnke 1991) option of the MENDEL linkage computer programs, which was then used to estimate marker allele frequencies. Chi square tests were used to ensure that all SNPs were in Hardy Weinberg equilibrium.
