Attention deficit hyperactivity disorder (ADHD) and autism are two different conditions and two different diagnoses.

Yet, there are many symptoms that overlap and occur in both disorders. They include poor social skills, sensory dysfunction, and the inability to stay focused.

This can make an accurate diagnosis more difficult. The difference is seen in the way these symptoms present and their severity, which can signal which condition is relevant.

The recently updated Diagnostic and Statistical Manual of Mental Disorders V permits both ADHD and autism diagnoses in one person, allowing a growing number of people to be diagnosed with both ADHD and autism spectrum disorder.

Autism Diagnosis

However, it isn’t always that simple. Since so many symptoms overlap, a clinician can attribute symptoms to the existing ADHD diagnosis, not seeing the signs of possibly coexisting autism.

A new study published in the journal Pediatrics found that children who are diagnosed with ADHD first are more likely to get their autism diagnosis at a later age than those with no ADHD diagnosis. The autism diagnosis comes an average of three years later for kids with an existing diagnosis of ADHD.

Read More: What Symptoms Do ADHD and Asperger’s Syndrome Share? »

A Mother’s Story

“As a baby, toddler, and preschooler, we always recognized our son was a bit different than other children his age,” Karen Copeland, founder of Champions for Community Mental Wellness, told Healthline. “It was kindergarten or grade one when I started strongly suspecting autism. Our son was diagnosed with ADHD by a pediatrician after a 15-minute interview when he was 6 years old.”

The subsequent experiences of Copeland and her son are an illustration of the study’s findings.

Despite suspecting that her son also had autism around age 6, he didn’t receive the additional diagnosis until age 11.

“That 15-minute [ADHD] diagnosis held more power than anything we, as our son's parents, could ever say,” Copeland explained. “Ten pages of documented observations of our child's social challenges, repetitive behaviors, and concrete and rigid thinking were dismissed outright. In fact, these were described as nonspecific concerns by a psychiatrist who held tremendous power over who qualified for assessment.”

The study’s authors advised, “To avoid potential delays in [autism] diagnosis, clinicians should consider [autism] in young children presenting with ADHD symptoms.”

Copeland agrees that the standard practices for diagnosing these conditions need to be improved, saying evaluations should include “more detailed observations in multiple environments, more interviews with support teams who are working with the child and family, and most importantly, listening to the parents.”

Read More: Treatment Options for ADHD »

Don’t Fear Double Diagnoses

Parents are often afraid of more than one diagnosis, but medical experts say they shouldn’t be.

Identifying additional existing conditions can lead to better and more effective treatment for a child’s struggles.

Keep an eye out for signs of coexisting autism if your child has a diagnosis of ADHD but you feel, as Copeland did, that doesn’t quite cover all the pieces of their challenging puzzle.

While many children with ADHD mature and get better at social interactions and emotional regulation as they get older, kids with coexisting autism often continue to have an ever-widening gap between themselves and their peers in these areas.

A continued lack of focus on hygiene, not understanding nonverbal cues, rigid thinking, meltdowns, and poor communication could signal the presence of autism as well.

If you suspect both conditions, seek an evaluation by a reputable professional versed in both ADHD and autism.

A self-described “veteran” parent of a son with ADHD and autism, Penny Williams is the author of two award-winning books on ADHD, “Boy Without Instructions: Surviving the Learning Curve of Parenting a Child with ADHD” and “What to Expect When You're Not Expecting ADHD.” Her third book, “The Insider’s Guide to ADHD: ADHD Adults Reveal the Secret to Parenting Kids with ADHD” will be available in December 2015.

Read More: The Relationship Between ADHD and Autism »