Gender differences in ADHD subtype comorbidity

Objective: To examine gender differences in attention-deficit/hyperactivity disorder (ADHD) symptom comorbidity with oppositional defiant disorder, conduct disorder', separation anxiety disorder, generalized anxiety disorder, speech therapy, and remedial reading in children. Method: From 1994 to 1995, data from a large sample (N = 4,371) of twins and siblings studied in the Australian Twin ADHD Project were obtained by mailed DSM-IV-based questionnaires, investigating patterns of comorbidity in the three subtypes of ADHD: inattentive, hyperactive/impulsive, and combined. A total of 1,550 questionnaires were returned (87%) over the next 12 to 18 months. Results: Analysis of variance showed significant between-group differences in males and females for inattention and hyperactive/impulsive symptom counts with higher rates of oppositional defiant disorder and conduct disorder in males, and higher rates of separation anxiety disorder in females indicating internalizing disorders are more common in females and externalizing disorders are occurring more often in males. Differences were found between the ADHD subtypes and the no ADHD category for all comorbid conditions, for both males and females. Children without ADHD consistently had fewer symptoms, while children with the combined subtype showed consistently more comorbid symptoms indicating a strong relationship between high rates of externalizing symptoms and high rates of internalizing symptoms. Gender differences in speech therapy were significant only for the children without ADHD. The rates of separation anxiety disorder were higher in females with the inattention subtype and the rate of generalized anxiety disorder higher for females with the combined subtype, indicating that the subtypes of ADHD were associated with these internalizing disorders in different ways. Conclusions: Although comorbidity differs among ADHD subtypes, there were no significant gender differences in comorbidity for externalizing disorders. Inattentive girls may present with anxiety. Clinical approaches for both males and females should be sensitive to possible language and reading problems.