VIPR2 and cocaine dependence: VIPR2 and PTPRN2 were significant in a linkage analysis of comorbid cocaine dependence and major depressive episode in humans.76 Further, Ptprn2 is significant in human GWASs for cognitive performance, risk taking, and smoking initiation.77 Copy number increases in Vipr2 are associated with schizophrenia and alter dopaminergic neurotransmission in engineered mice.78Ptprn2 knockout mice show decreased brain dopamine, norepinephrine, and serotonin concentrations.79