Study Suggests One-Third of Children With Autism Also Have ADHD

Many children with autism also have ADHD symptoms

Nearly one-third of children with autism spectrum disorder (ASD) also have clinically significant symptoms of attention deficit hyperactivity disorder (ADHD), according to researchers. That's three times higher than the incidence in the general population. The study, "Association between severity of behavioral phenotype and comorbid attention deficit hyperactivity disorder symptoms in children with autism spectrum disorders" published in Autism: The International Journal and Practice (online June 5, 2013), also found that children with the combined presence of ASD and ADHD face greater impairments and have more difficulty learning and socializing as compared to children with ASD only.

A young boy playing with his blocks
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How Autism and ADHD Are Similar and Different?

Both ASD and ADHD are neurodevelopmental disorders with the onset of symptoms in childhood. ASD is characterized by impairments in communication and social reciprocity and stereotypic and/or repetitive behaviors, with symptoms presenting in early childhood. ADHD is characterized by developmentally inappropriate levels of inattention, impulsivity, and/or hyperactivity and presents prior to age 12 years. Symptoms associated with both ASD and ADHD cause significant behavioral, social, and adaptive problems across home, school, and community settings.

Though symptoms of ADHD are often noted in children with ASD, until recently ASD and ADHD could not be officially diagnosed together under diagnostic guidelines. In May 2013, the Fifth Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) was released and this updated edition allows for a dual diagnosis of ASD and ADHD.

"We are increasingly seeing that these two disorders co-occur and a greater understanding of how they relate to each other could ultimately improve outcomes and quality of life for this subset of children," says Dr. Rebecca Landa, senior study author and director of the Center for Autism and Related Disorders at Kennedy Krieger in Baltimore, MD. "The recent change to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) to remove the prohibition of a dual diagnosis of autism and ADHD is an important step forward."

Study Findings Highlight Connection

The study examined rates of parent-reported clinically significant symptoms of ADHD in early school-age children (four to eight years old) with ASD. "We focused on young school-aged children because the earlier we can identify this subset of children, the earlier we can design specialized interventions," says Dr. Landa. "Tailored interventions may improve their outcomes, which tend to be significantly worse than those of peers with autism only."

Participants included 162 children enrolled in a prospective, longitudinal study of child development. Children were first divided into ASD and non-ASD groups. They were then further categorized according to parent-reported symptoms of ADHD. Out of 63 children diagnosed with ASD, 18 (29 percent) were rated by their parents as having clinically significant symptoms of ADHD. Children with ASD and ADHD were also found to have lower cognitive functioning, more severe social impairment, and greater delays in adaptive functioning than children with ASD only.

These findings highlight the need to assess for ADHD symptoms at an early age in children diagnosed with ASD. When ASD and ADHD occur together there is greater risk for increased level of impairment. When symptoms of ADHD remain unrecognized and untreated, positive outcomes are decreased. Research is needed to determine effective interventions for young children with ASD with comorbid ADHD in order to optimize outcomes for these children and families.

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  • National Institutes of Health, "Autism, ADHD Often Occur Together, Research Shows," MedlinePlus/HealthDay. 

  • Rao PA, Landa RJ. Association between severity of behavioral phenotype and comorbid attention deficit hyperactivity disorder symptoms in children with autism spectrum disorders. Autism. 2014;18(3):272-80. doi:10.1177/1362361312470494