Autism Spectrum Disorders in Children and Adolescents with Attention Deficit Hyperactivity Disorder

Background: Attention deficit hyperactivity disorder (ADHD) is characterized by severe inattention, hyperactivity, and impulsivity. Autism spectrum disorders (ASD) are characterized by impairments in social interaction and communication as well as repetitive and restricted behavior and interests. Current classification systems (ICD-10, DSM-IV) do not allow for a comorbid diagnosis of ASD and ADHD and there is a hierarchy of diagnosis, whereby a diagnosis of ASD overturns that of ADHD. Despite the diagnostic rules, many research studies have documented coexistence of ASD and ADHD diagnoses. ADHD and ASD appear to often co-occur in families. Several studies reported that 30–80% of children with ASD meet criteria for ADHD and 20–50% of children with ADHD meet criteria for ASD.

Objectives:  We aim to investigate the frequency of autism spectrum disorders in clinic-referred children with ADHD and compare  psychiatric comorbidity between children with ASD plus ADHD and only ADHD.

Methods: A consecutive series of 147 children and adolescents (mean age, 9.95 ± 3.02 y) with a diagnosis of ADHD were included in the study. All cases were interviewed by the first author for autism spectrum disorders according to DSM-IV criteria. Psychiatric co-morbidity was assessed using the Schedule for Affective Disorders and Schizophrenia for School Age Children-Present and Lifetime Version (K-SADS-PL-T).

Results:  Fourteen cases (9.5 %) were diagnosed as having a comorbid ASD (3 with autistic disorder, 3 with Asperger syndrome and 8 with PDD-NOS). Subjects with ASD plus ADHD were compared with subjects with ADHD without ASD. Hyperactive-impulsive subtype was more frequent in ADHD plus ASD group. ADHD and ASD comorbidity was significantly associated with a higher rate of males. Frequency of psychiatric disorders was higher in ADHD and ASD group.

Conclusions: Family and twin studies supported the hypothesis that ADHD and ASD originate from partly similar genetic factors. A screening for ASD should be performed in patients with ADHD, as these patients and their parents are frequently not aware that the impairment may be partly due to a comorbid ASD.