The GWAS results are summarized in Figure 2 and the quantile-quantile plot is shown in Figure S1 in the Supplemental Material available online. The genomic inflation factor, which is mathematically defined as the ratio of the median of the observed distribution of the GWAS test statistic to the expected median (Devlin & Roeder, 1999) was acceptable, λ = 1.01. Extreme deviations in λ indicate an excess false positive rate, (i.e., inflation) in a GWAS, which may be attributable to technical problems in the genotyping or uncontrolled population stratification. Thus, in our study, technical issues and population stratification did not appear to inflate the results. The most associated SNP (p = 2.37 × 10-07) was located in zinc finger protein 407 (ZNF407) on chromosome 18.
