2; GAIN-MDD-PS: P < 0.001; and PGC-MDD-PS: P < 0.2) to assess whether the effects of PS were larger at high levels of depression scores. Unlike linear regression models, which assess whether the mean value of the phenotype differs by PS level (the mean model), quantile regression models assess whether a specific percentile, for example, the median, differs by PS. Quantile regression was performed in the Statistical Analysis Systems software package, version 9.3 (SAS Institute, Inc., Cary,

Inhibitors,research,lifescience,medical NC). Coefficients for each decile in each of the four GWA substudies were estimated and then meta-analyzed (with inverse variance weighting). We bootstrapped (5000 replications) to test the association between each of the three PS approaches and the interquartile

Inhibitors,research,lifescience,medical range for the depression measure. A P-value <0.05 was considered a significant association with depression scores in quantile regressions. Results Initial analyses The 14-year long-term average depression score of 6989 women in the study had a mean of 1.83 with standard deviation (SD) of 0.65, consistent with that in the full NHS cohort. The analytic sample did not appreciably differ from the larger cohort across a range of demographic and other sample attributes (Table 1). Table 1 Characteristics of NHS full sample versus genetic study participants. The Cronbach's alpha for the seven-wave depression score Inhibitors,research,lifescience,medical was 0.83, suggesting these depression assessments measure a unified underlying attribute. In the full NHS cohort (N = 106,020), the long-term average depression score was significantly positively associated with cigarette smoking and negatively associated with physical activity (both P's for trend <0.0001). The association between BMI and depression score was U-shaped (P < 0.0001), such that both underweight and overweight Inhibitors,research,lifescience,medical women had higher depression scores than normal-weight women (Fig. 1). Figure 1 Distributions of behaviors and

BMI in relation to the 14-year long-term average composite depression phenotype in the full NHS cohort (N = 106,020). BMI, body mass index; NHS, Nurses’ Health Study. Meta-analyzed genome-wide SNP Inhibitors,research,lifescience,medical associations The genomic inflation factor (lambda) for each substudy ranged between 1.00 and 1.01. The QQ-plot (Fig. 2) indicated good adherence of observed meta-analyzed P-values to the line and of expectance, suggesting little evidence of Selleck 5 FU systematic genotyping error. No individual SNPs reached the conventional genome-wide significance threshold of 5 × 10−8 for the association with long-term average depression score (Fig. 3). The SNP with the lowest P-value was rs6763048 (P = 8.42 × 10−7), mapping to an intron of SCN5A on chromosome 3. A total of 14 SNPs had P-values <1 × 10−5, corresponding to eight independent SNPs (r2 < 0.05 in 500 kb) (Table 2). Table 2 Meta-analysis GWAS results of 14-year long-term average composite depression measure of top findings (P < 10−5) in four NHS substudies (N = 6989).