A QQ plot of the p-values for the genotyped SNPs (supplementary material File S1) suggested negligible inflation due to population structure or cryptic relatedness (genomic control λ = 1.014), but also little evidence of p-values below those expected under the null hypothesis. Results from the main-effects analyses are shown in Figure 1a, and Table 1. Both genotyped and imputed SNPs within the gene ARRDC4, at the distal end of 15q, almost reached p = 10−6. We identified several imputed SNPs with p<10−6 on 6q, within the gene NKAIN2, which has not previously been reported in linkage or association studies, although the strongest association at a genotyped SNP (rs11154221) in this gene has p≈10−4. No SNP showed a notable interaction with sex (Figure 1b). SNP by age interaction analyses revealed multiple associations at the distal end of 13q within gene GPC6 (Figure 1c, Table 1). The strongest signal (p≈10−7) was at a genotyped SNP, rs9561329; EPQ score tends to increase with age for carriers of the minor allele, and decreases for non-carriers (Figure 2). Conditional regression analyses revealed that the signal
