Our gene-based test of 17,601 genes on autosomal chromosomes yielded two genes associated with delta power that survive Bonferroni correction (α = 2.84 × 10−6): DEFA4 and DEFA6 on chromosome 8 (both p-values < 1 × 10−6). Both encode defensins, a family of peptides thought to be involved in host defense. DEFA4 encodes a protein expressed in neutrophils (leukocytes) (i.e., in the blood) that inhibits corticotropin stimulated corticosterone production, and DEFA6 encodes a protein that is highly expressed in the bowel. These two genes are located in close proximity to each other. We followed up this finding by using RFGLS to analyze SNPs imputed with reference to 1000 Genomes to provide denser coverage of this region than the Illumina array provided. Results are plotted in Figure S8 in the supplement to this article. None of the imputed SNPs yielded a genome-wide significant p-value. The smallest p-values largely fall between the two genes and appear to represent a single signal.
