were excluded. All SNPs were genotyped in a subset of samples in replicate reactions to determine the genotyping error rate. Five SNPs (rs1127313, rs7543174, rs2072660, rs3787140 and rs3787138) had an error rate above 1% and thus were excluded from further analysis; the remaining SNPs had an average error rate of 0.4%. In total 15 SNPs (Figure 1) were included in the analysis. Mendelian errors were detected using PLINK’s (http://pngu.mgh.harvard.edu/purcell/plink/; Purcell et al. 2007) mendel option. If there was a Mendelian error detected in only 1 SNP within a family, this was considered to be sporadic and the genotypes for that family at the single SNP were removed. If there were 2 or more Mendelian errors detected within a family, the genotypes of the entire family were removed at all loci.
