APP and attention deficit-hyperactivity disorder: Third, children with trisomy 21, who over-express APP and have overwhelmingly high rates of AD (Wiseman et al., 2015), also have significantly elevated rates (43.9%) of ADHD symptoms (Ekstein et al., 2011) compared to the rates of ADHD in the general population (up to 7.1%; Willcutt, 2012).