ND patients harboring deletions or mutations affecting not only NDP but also MAO-A and/or MAO-B (which are neighboring genes to NDP) exhibit differential phenotypes; unlike patients with either MAO-A or combined MAO-A/MAO-B deficiency, patients with selective MAO-B deficiency (i.e., total lack of platelet MAO-B activity) failed to exhibit overt pathological behavior55. This evidence concerns the gene MAOB and Norrie disease.