Using annotation provided in the Illumina 450K HumanMethylation Beadchip, 12 CpG sites were found to be within the OXTR associated CpG island. Consistent with prior studies (Kim et al, 2014; Simons et al., in press), the results of a principal component analysis suggested four orthogonal factors with eigenvalues greater than 1. Tabled results of the PCA are available in the supplemental material (Table S1). Consistent with prior research we identified a set of three CpGs (factor 4; cg09353063, cg17285225, and cg23391006) that cohered as a factor, were physically contiguous, and were located on the first exon of OXTR, suggesting strong potential for regulatory impact. The location of these loci is shown in the supplemental material (Figure S1), and they are identical to the set found previously in a different sample of African American adults by Simons et al. (in press). Accordingly, we standardized and then averaged the beta scores for each of the three loci to form our index of OXTR methylation.
