First, female individuals with ADHD may have a higher than expected risk of comorbid severe conditions and so may have a higher level of clinical heterogeneity as compared with male cases. This could indirectly point to a greater role of rare deleterious variants in female individuals with ADHD because such variants are strongly implicated in some of the comorbid conditions assessed 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 and this effect has been seen in other neurodevelopmental disorders 15, 16, 17, 18, 19. However, this needs to be tested directly because common variants also play an important role in such complex disorders 41, 42, and little is currently known about the contribution of rare variants to ADHD.
