The separation of ADHD inattention and hyperactivity-impulsivity symptoms: pathways from genetic effects to cognitive impairments and symptoms

This study looked at ADHD, a condition with two main types of symptoms: not being able to focus (inattention) and being very active or impulsive (hyperactivity-impulsivity). The researchers wanted to find out if these symptoms are caused by the same or different genetic factors. They also explored whether problems with thinking skills, often seen in people with ADHD, are linked to these two types of symptoms differently.

To do this, the team used a special method to analyze the genes and thinking skills of 1312 kids, aged 7 to 10. They had the kids do tasks that tested how quickly and accurately they could respond to things, like the go/no-go and fast tasks, which are like quick reaction games.

The study examined the relationship between cognitive impairments in children with ADHD and their genetic factors. It focused on two specific cognitive impairments: reaction time variability (RTV) and commission errors (CE). RTV measures the consistency of a child's reaction times, while CE refers to mistakes made during tasks where they are supposed to wait.

The findings revealed a substantial genetic overlap between reaction time variability (RTV) and inattention symptoms of ADHD. This was quantified by an additive genetic correlation of 0.64. In contrast, the genetic correlation between RTV and hyperactivity-impulsivity symptoms was significantly lower, at 0.31.

The study also explored the genetic correlations of CE with ADHD symptoms. CE showed low genetic correlations with both hyperactivity-impulsivity and inattention, with correlations of 0.17 and 0.11 respectively. This suggests that making errors during tasks requiring patience is not strongly linked to the typical symptoms of ADHD.

Furthermore, the genetic correlation between RTV and CE was low and non-significant, indicating an etiological separation between these two cognitive impairments. This supports the idea that different genetic factors in children with ADHD might be responsible for RTV and CE.

Overall, these findings underscore the different genetic relationships that RTV and CE have with the two primary symptom domains of ADHD, namely inattention and hyperactivity-impulsivity. This research contributes to a more nuanced understanding of the genetic underpinnings of ADHD and its associated cognitive impairments.

In summary, the study shows that the two main types of ADHD symptoms (not being able to focus and being too active or impulsive) might be caused by different genes. The researchers found a strong genetic link between having inconsistent reaction times and not being able to focus, but they didn't find this kind of link for making mistakes when waiting and either type of ADHD symptom.

Reaction time variability is one of the most validated indicators of ADHD. This study adds to our understanding of ADHD by connecting reaction time variability to inattention. For example, one study found that those with ADHD don’t necessarily respond slower. However, they tend to lose focus sometimes when asked to perform tasks