KLK8 and attention deficit-hyperactivity disorder: However, in terms of common variation, no genome-wide significant association could be found between variants in the KLK8 locus and mental disorders in the currently largest major depressive disorder (MDD), SZ, bipolar disorder (BD), ASD or attention deficit hyperactivity disorder (ADHD) genome-wide association studies (GWASs) [58–62] (Fig. 5 and Additional file 1: Figure S2).