There has been conflicting information on the association between ADHD and autism. A study published in 20122 suggested that there was a genetic link between the two disorders. And the new Diagnostic and Statistical Manual 5 (DSM-5) allows for dual diagnosis, however, the previous DSM suggested that someone with autism could not be diagnosed with ADHD. The most recent study, completed by researchers at the Kennedy Krieger Institute and published in Autusm: The International Journal and Practice, shows that one-third of children diagnosed with autism also have ADHD.
What is Autism?
Autism spectrum disorder (ASD) is a developmental disorder characterized by "difficulties in social interaction, verbal and nonverbal communication and repetitive behaviors" ASD can be associated with intellectual disability, difficulties in motor coordination and attention and physical health issues such as sleep and gastrointestinal disturbances."  Recent research shows that one in every 50 children has autism. .
Although ASD probably occurs during a fetus' brain development, signs of autism are often noticed by parents and medical professionals between the ages of 2 and 3. Some early signs of autism in toddlers include:
- Not making eye contact
- Not smiling when smiled to
- Not responding to name or familiar voices
- Not visually following objects
- Not pointing or waving good-bye
- Doesn't initiate or respond to cuddling
- Doesn't make noises or imitate movements
- Doesn't reach out to be picked up
- Disinterested or unaware of people around them
According to a study completed in 2007, 1 in 86 children have autism but a more recent study, published in March, 2013, suggests that as many as 1 in every 50 children have autism.
Connection Between ADHD and Autism
The study completed at the Kennedy Krieger Institute shows that one-third of children diagnosed with ASD also exhibited symptoms of ADHD. Scientists followed 162 children from birth to 8 years old. During this time, 63 of the children were diagnosed with ASD and of them, 18 were also diagnosed with ADHD. The difference between this and others studies is that, for the current study, children were recruited as infants or toddlers, before a diagnosis was made. Researchers believe previous studies may not provide accurate results because participants came from a pool of children whose parents were seeking medical care and, therefore, may have been showing more severe symptoms.
Rebecca Landa, author of the study, indicated that the children with symptoms of both ASD and ADHD "have significanlly more trouble in school than students who have only autism and students who had both scored worse on cognitive and social functioning tests. Children with both disorders were also more likely to display 'severe autism mannerisms' such as repetitive behaviors." 
Landa believes that a better understanding of the connection between these two disorders can help offer children with both a better quality of life.
Nearly One-Third of Children with Autism Also Have ADHD," 2013, June 5, Staff Writer, ScienceDaily
  Study: A Third of Autistic Children Also Have ADHD," 2013, June 5, Jason Koebler, U.S. News and World Report
 "What is Autism?" Date Unknown, Staff writer, AutismSpeaks.org