Sex differences in symptom presentation may influence the sex ratio in neurodevelopmental disorders, such as ADHD and ASD. Among cases of ADHD, approximately 80% of child clinic cases are male, whereas this decreases to approximately 50% in adult clinics. It has been hypothesized that boys show higher levels of hyperactivity and impulsivity, while girls manifest more inattentive symptoms and tend to be less disruptive, 20 and therefore less likely to receive a diagnosis. Similarly, it has been suggested that the sex ratio in ASD is the result of underdiagnosis in girls, because they tend to develop and maintain more language and cognitive skills than do boys. In addition, boys show higher levels of restricted/repetitive behaviors and interests than females, whereas there appear to be no gender differences in social interaction or communication overall. 21 Although the prevalence of schizophrenia is approximately equal in males and females, males with this disorder also have been shown to suffer from more severe symptoms, course and impact than females. 22
