Understanding of the genetic and phenotypic (characteristic expression) overlap of ADHD and Autism is relatively new. Until recently, if a patient presented with symptoms of both conditions, the clinician had to choose which diagnosis fits best. While co-occurrence is common, it is also common to see elevated ADHD traits within Autistics or elevated Autistic traits for the ADHDer. A child may not meet the criteria of both and yet still have significant trait overlap.