New research shows that almost one-third of children aged between 4 and 8 years who are diagnosed with autism spectrum disorder (ASD) also have attention-deficit/hyperactivity disorder (ADHD).
While the two conditions are separate disorders, those who have both conditions are far more likely to have lower cognitive function, to be more severely impaired socially, and to have greater delays in adaptive functioning than those children with ASD alone.
The research was conducted at the Baltimore-based Kennedy Krieger Institute. Of the total 162 participants, 63 children were diagnosed with an ASD, of whom 29% showed clinically significant ADHD symptoms. Of those 18 children with both disorders, almost two thirds (61%) had significant cognitive delays and more severe autism mannerisms, such as repetitive behaviors, versus 25% of those with an ASD alone. Also, those with both disorders had significantly more problems at school and in their functioning abilities in everyday situations.
This longitudinal child development study used parent reports and included children enrolled in the protocol as toddlers, which is before most cases of ADHD are identified.
Researchers focused specifically on younger children because the earlier this subset of children is identified, the earlier appropriate interventions can be offered, which may, in turn, improve outcomes.
Source: Contemporary Pediatrics, June 11, 2013
The Association for Adults with Autism, Philippines is a non-profit association, established by parents of individuals within the Autism Spectrum Disorder (ASD) and professionals dedicated to the welfare of those with this developmental disorder. 
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