Specifically, one study found that both PTPRN2 and DLGAP2 contained a large number of variable number of tandem repeats that were expressed in the brain, some of which ultimately correlated with attention-deficit hyperactivity disorder, SZ, bipolar disorder, and depression in relation to cocaine addiction (Linthorst et al., 2020). This evidence concerns the gene PTPRN2 and depressive symptom measurement.