Lastly, we set out to determine whether or not SLC1A1 is also associated with differential OCD symptom presentation, given the growing appreciation of OCD as a clinically, and possibly etiologically, heterogeneous disorder.38,41-43 We performed subphenotype analyses on the basis of Y-BOCS–ascertained OCD symptom severity and the hoarding phenotype evaluated by 2 measures: (1) a Y-BOCS factor analysis–derived hoarding symptom dimension,37 and (2) the magnitude of hoarding symptoms, as indexed by the SIR.39,44 We observed a nominally significant association of 1 eQTL SNP, rs3933331, with the hoarding phenotype. Specifically, this SNP was significantly associated with hoarding as assessed by both the Y-BOCS hoarding symptom dimension (β=.21, t216=2.9, P=.005) and total SIR scores (β=.19, t198=2.6, P=.009). That is, greater scores on the hoarding dimension, as well as more severe SIR symptom scores, were strongly correlated with the number of G alleles at rs3933331 (Figure 2). The association with SIR scores appears to be largely driven by the acquisitioning subscale (β=.22, P=.002), as rs3933331 was less strongly associated with the clutter (β=.18, P=.01) and difficulty discarding (β=.115, P>.05) subscales.
