PKP4 and Borderline personality disorder: So far, one case-control GWAS, i.e. comparing BPD patients diagnosed using established diagnostic systems to controls, has been performed which did not identify associated single variants but indicated significant gene-based associations in the genes coding for dihydropyrimidine dehydrogenase (DPYD) and plakophilin-4 (PKP4), which have been previously linked to other mental disorders, e.g. schizophrenia [12].