observation potentially serves as independent evidence for association of markers in this region. DLGAP1 is a member of the neuronal postsynaptic density complex and is in the same family as the DLGAP3 gene, which has been shown in a convincing way to be responsible for OCD-like behaviors in DLGAP3 knockout mice models 54. A marker in the second genetic region (harboring GRIK2), also a top signal in the IOCDF-GC GWAS showed nominal significance in our study (P=0.045). Although failing to reach experiment-wise significance it is of note that DLGAP1 and GRIK2 interact (FUNCOUP 34). Following up these signals in a gene-set analysis for high confidence interaction partners of DLGAP1 and GRIK2 (identified using FUNCOUP 34) showed a trend for association and pointed to a potential role of a set of DLGAP1 and GRIK2 interactors in the etiology of OCD, involving genes such as NEUROD6, SV2A, GRIA4, and SLC1A2. Interestingly PTPRD was part of this gene set. It is of note that for both DLGAP1 and GRIK2 we identified more then 160 interactors each, thus indicating they are highly connected nodes (hubs) in the interactome. Earlier findings have suggested that only genes that are essential in (early) development (“essential genes”) tend
