Opinion Conversations on the science of autism research.

Restricted behaviors link autism, attention deficit

by ,  /  10 October 2014

Tinca Polderman; Henrik Larsson.

Autism and attention deficit hyperactivity disorder (ADHD) are distinct conditions that coexist in some children and adults. Our new study, published 2 September in Translational Psychiatry, suggests that individuals who have both disorders tend to share specific symptoms, such as repetitive and restricted patterns of behavior, inattention and hyperactivity1. It also supports a genetic link between autism and ADHD.

Up to 44 percent of people diagnosed with autism also meet the criteria for ADHD2. What’s more, the two disorders tend to run in the same families. That led us to investigate whether people with both autism and ADHD express a specific subset of symptoms that stem from shared genetic or environmental factors.

We used questionnaires to probe the existence and severity of autism and ADHD symptoms among 17,770 Swedish adult twins who participated in the Swedish Twin Study of Adults: Genes and Environments.

We found that repetitive and restricted behavior in autism is most strongly associated with inattention and hyperactivity in ADHD. This makes intuitive sense because restricted behaviors can interfere with the ability to switch attention from one task to another. Social and communication deficits in autism are also tied to inattention and hyperactivity in ADHD, but this association is weaker.

Studying identical and fraternal twins allowed us to take the analysis one step further and examine how genetic and environmental factors contribute to the association between autism and ADHD. We found that genetic factors account for the link more than environmental factors do, and that the genetic link is strongest between repetitive and restricted behavior in autism and inattention and hyperactivity in ADHD. This held true for men and women.

The findings are in line with those from our study of Dutch adults published last December. In that study, we found that the co-occurrence of autism and ADHD in adults stems from the inability to easily switch attention from one task to another. We also found this link to be genetic in nature3.

Taken together, these results suggest that the overlap between autism and ADHD in adults stems from the simultaneous manifestation of specific symptoms of both disorders.

This knowledge may help guide the treatment of both disorders. For instance, treating repetitive and restrictive behavior may improve inattention and hyperactivity in people with both autism and ADHD.

The findings may also help researchers find genes underlying these disorders. Because the genetic overlap between autism and ADHD appears to be symptom-specific, this could help researchers narrow the search for mutations to people with those symptoms.

Tinca Polderman is assistant professor of complex trait genetics at VU University Amsterdam in the Netherlands. Henrik Larsson is assistant professor of medical epidemiology at the Karolinksa Institute in Stockholm, Sweden.


1: Polderman T.J. et al. Transl. Psychiatry 4, e435 (2014) PubMed

2: Lai M.C. et al. Lancet 383, 896-910 (2014) PubMed

3: Polderman T.J. et al. Psychol. Med. 43, 1985-1996 (2013) PubMed

11 responses to “Restricted behaviors link autism, attention deficit”

  1. Alexandria says:

    Very interesting and useful research! However, I don’t understand the logic of these statements: “We found that repetitive and restricted behavior in autism is most strongly associated with inattention and hyperactivity in ADHD. This makes intuitive sense because restricted behaviors can interfere with the ability to switch attention from one task to another”. Isn’t the repetitive and/ or restricted behaviour in autism caused essentially by concentrating too much on the object of interest at hand? So, really, the opposite of the inattention in ADHD, where the behaviour is caused by being unable to concentrate on one thing at a time? It doesn’t make intuitive sense to me at all that two opposite behaviours may have the same genetic basis. I also don’t understand how treating one of the behaviours may help resolve or ease a completely opposite behaviour. Anyway, I hope somebody can explain it to me.

    • Erica says:

      I, too, was struck by that statement, and I do not have the expertise to explain any of this. Knowing people with OCD and with ADHD has suggested a kinship between some OCD and some ADHD. These conditions are in some sense opposites, yet they also share much. For instance, both conditions can involve hyperfocus. Also, both can find sufferers struggling to direct attention where it’s needed.

  2. Tinca Polderman says:

    Thanks to both interested readers of our blog ‘Restricted behaviors link autism and ADHD’! We too, were puzzled by our findings of ‘not being able to switch attention’ [in two Dutch samples] and ‘restricted and repetitive behavior’ [in a Swedish sample], being the most important link between autistic traits and ADHD. One of our first thoughts was that this pattern of co-occurrence would be specific for adults. However, a recent study by Ronald et al. [2014, Journal of Abnormal Psychology] reported similar findings between ‘restricted and repetitive behaviors’ and ADHD traits in a sample of 9 and 12-year old children from the UK. Thus, our findings seem to be rather robust across ages, and across countries. Our interpretation of the data now is that ‘being too focused on one thing or task’ and as such not being able to divide attention between tasks [which is often necessary in daily life!] more or less mirrors the general inattention problems of ADHD. A term like ‘attentional flexibility problems’ would maybe capture this mechanism best?

  3. Sekhmes says:

    On many ADD forums, many often state that they have issues with hyperfocus as the other side of inattention. The inattention in many people with ADHD is that they find it difficult to switch whether they are hyperfocusing or not able to focus, it’s a difficult with changing focus.

  4. Julie says:

    I have ADHD. I’m either unfocused or hyperfocused. My brother with HFA has the same difficulty. It seems that there is a distinct misunderstanding of ADHD.

  5. MLuján says:

    Idont understand why the PANDAS-PITAND-PANS is not properly included in the analysis of these symptoms, especially with the immune dysfunction, autoimmunity -prone biology ( including susceptibility in families) and mito dysfunction present in several subgroups in ASD.
    New manuscript-Consensus is very interesting
    Clinical Evaluation of Youth with Pediatric Acute Onset Neuropsychiatric Syndrome (PANS): Recommendations from the 2013 PANS Consensus Conference

  6. Anonymous says:

    ‘treat repetitive restricted behavior?’
    i’m autistic, and these are the behaviors that are often quite soothing for me. it’s a tough world for autistics, it’s often the reward of returning home at the end of a day and being able to pursue my interests that gets me through the day. i don’t agree in the slightest that we need to ‘treat’ these behaviors.

  7. Tinca Polderman says:

    Dear anonymous, you are absolutely right regarding the sample in the Ronald et al. study. Dr. Ronald is from the UK but the child sample she used to do this study was Swedish, my apologies for this mistake.

    Regarding ‘treatment of repetitive and restricted behavior’: treatment is of course only appropriate when people want treatment, for instance when particular behavior really hinders them during work, at school, or in their daily functioning in general.

    In all other cases, I would strongly encourage everyone to embrace the behaviors that make them feel happy, calm and comfortable!

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