DDAH1 and attention deficit-hyperactivity disorder: As for ADHD, a pediatric onset disorder typically lacking stereotypies but characterized by presence of other forms of ARB, nine of the 15 identified proteins are disorder associated biomarkers (i.e., Prdx5, Ahr, Ddah1, Dlk1, Gcg, Parp1, Pdgfb, Plxna4, Qdpr; see Fig 4b).