**5.6 ADHD comorbidity theories**

Evidence suggests that core ADHD symptoms and associated externalising disorders are overrepresented in both groups of interest, young people with neurodiversity and young people with gender variance. One large retrospective study had a surprising finding of a significant overrepresentation of gender variance, occurring 6.64 times more frequently among children with ADHD, than among a non-referred comparison group [47]. This study determined that parental report of gender variance was significantly greater in two groups of children, ASD group (5.4%) and ADHD group (4.8%) that collectively represent children with neurodevelopmental disorders, while the proportion of children with gender variance among combined medical group (1.7%) and non-referred comparison group (0–0.7%) were statistically different from ASD and ADHD groups; gender variance occurred equally in girls and boys [47]. In ADHD, impulse control difficulties are essential criteria for diagnosis and could potentially affect gender expression by reducing ability to inhibit primary gender impulses in spite of societal pressure to conform to gender stereotype [47]. Among transgender youth with ASD, children and adolescents may be less aware of the social stereotypes, hence the ASD/ADHD cohort are likely to ignore the societal influences against cross-gender expression and express their gender inclinations more freely or even parade their feelings of gender incongruence as an oppositional response to unaccepted societal rules.
