Comorbidity is one of the scariest-sounding words in medicine, but its meaning is deceptively simple. Comorbidity refers to the simultaneous presence of two or more chronic diseases or conditions. People with autism spectrum disorder (ASD) frequently have other comorbid conditions, one of the most common of which is Attention-deficit/hyperactivity disorder (ADHD). Here’s everything you need to know about the connection between ADHD and autism.

What do ADHD and autism have in common? ADHD and autism are distinct conditions, but they do present similarly. Both ADHD and ASD, for example, can cause problems with focus and impulse control and lead to communication difficulties. People with ADHD and people on the spectrum may both experience trouble in school and in personal relationships and social situations.

It’s not surprising, though, that ADHD and ASD present with such similar symptoms. Both disorders affect the central nervous system, which governs movement, language, memory, and social and focusing skills. Both conditions affect brain development and impact executive functioning, which controls high-level mental tasks like decision-making, organization, time management, and impulse control.

In some cases, the same medications can even be used to treat both conditions. Specifically, ADHD medications are sometimes prescribed to people with ASD to help decrease impulsivity and hyperactivity.

How are ADHD and autism different? While ADHD and autism have several symptoms in common, their underlying causes differ greatly. ADHD is a neurodevelopmental disorder that affects how the brain grows and develops, while ASD refers to a series of related developmental disorders that can impact language skills, behavior, social interactions, and the ability to learn.

ADHD and ASD look incredibly similar, but there are some ways to differentiate between the two. For example, while patients with ADHD and ASD both struggle to pay attention, there are nuances to look out for that will differ between the two. A child with autism will typically struggle to focus on things they don’t like and will often fixate intently on the things that they do like. Kids with ADHD on the other hand, tend to come to dislike and avoid the things they struggle to concentrate on.

While children with ADHD and autism are both likely to struggle with communication, the cause of those struggles differs in significant ways. Kids on the spectrum tend to lack social awareness and have a hard time expressing feelings and making eye contact. Children with ADHD, however, are more likely to talk incessantly, interrupt others, and attempt to monopolize conversations, possibly alienating others in the process.

Treatment for ADHD and autism also differ. ADHD treatment usually includes medication, while ASD treatment typically focuses on behavior therapy and skills training.

Are ADHD and autism connected? Although ADHD and autism aren’t directly connected, the conditions are frequently known to go hand-in-hand. In fact, the Centers for Disease Control and Prevention (CDC), reports that 14 percent of children with ADHD are also on the spectrum. By some estimates, 30 to 80 percent of children with autism also meet the criteria for ADHD and 20 to 50 percent of children diagnosed with ADHD also meet the criteria for autism.

When the conditions overlap, symptoms of both can become more intense. A 2013 study found that children with both ADHD and ASD experienced more difficulties with learning and social interactions than children with only one of the conditions.

Both ADHD and autism are more common in boys than in girls and both can present in adults as well as children (although having both is more common in children than in adults). Several studies have found that ADHD and ASD often overlap, but scientists still don’t understand why the comorbidity between the two is so common and more research remains to be done into the connection between ADHD and autism.