Attention deficit hyperactivity disorder

What most people know—or think they know—about attention deficit disorder, or ADD, is that it’s used to describe somebody who can’t stay focused…and when they REALLY can’t focus, they have attention deficit hyperactivity disorder, or ADHD. This continuum from one to the next isn’t quite how it works, though.

ADD and ADHD are actually synonymous, as in, they’re the same. ADD is an outdated term used prior to 1987, after which it evolved into ADHD to encompass more of the symptoms that people with ADHD often experience, which in addition to being inattentive, includes both hyperactivity and impulsiveness. So somebody might be diagnosed with ADHD because they have symptoms related to not being able to pay attention, but they also might be diagnosed with ADHD if they have symptoms relating to being overly active and impulsive. They might also have ADHD if they have symptoms of both.

According to the diagnostic and statistical manual for mental disorders, the Fifth Edition, text revision, the most recent update being in 2022, ADHD is split into these 3 subtypes: inattentive, hyperactive-impulsive, or both.

Inattentive and hyperactive-impulsive each have a set of 9 symptoms. For example, someone with the inattentive subtype might make careless mistakes, or not listen, or be easily distracted; and someone with the hyperactivity and impulsive subtype might fidget, or squirm around, or get up from their chair often.

Now, you might be thinking that everyone fidgets now and then, right? Well a diagnosis is given when someone has 6 of the 9 symptoms for either subtype for at least 6 months occurring in more than one setting. Most commonly though, children have symptoms of both subtypes and therefore have the combined subtype.

Since ADHD is considered a neurodevelopmental disorder, the symptoms also have to have started between age 6 and 12, and the behavior can’t be appropriate for their age or developmental level.

Alright, but what causes someone to be hyperactive, or impulsive, or inattentive? Well, as you might guess, it’s pretty complicated...and we don’t really know, probably a lot of different factors, and ultimately they all fall into some combination of environmental and genetic factors.

One interesting clue to a genetic component of ADHD is looking at families—for example, a child with a sibling that’s been diagnosed with ADHD is more likely to develop it themselves. Furthermore, if those siblings are identical twins, meaning they have the same DNA, their chances of developing ADHD is considerably higher. Having identical DNA doesn’t mean that the twin is definitely going to develop ADHD, though, which again, suggests that both genetic factors and environmental factors play a part.

As to a specific gene, it’s probably not one single gene that leads to ADHD, but rather multiple genes that determine how severe their symptoms are. These genes likely influence the production or regulation of the brain’s neurotransmitters, which are signaling molecules in the brain that are released by one neuron, and received by receptors of another neuron. This movement from a neurotransmitter from neuron A to neuron B is basically a message being relayed—it’s like the neurons are talking.