The ‘Genetic Basis of ADHD’ – much ado about nothing

The Holy Grail for many proponents of ADHD is establishing its ‘genetic basis’. The logic being that establishing a genetic basis for ADHD validates it as a psychiatric disorder. In September 2010 the world’s media buzzed with the news that British researcher’s had proven the genetic basis of ADHD. The psychiatrist who led the study, Cardiff University Professor Anita Thapar, proclaimed ‘now we can say with confidence that ADHD is a genetic disease.’^[1]

Professor Thapar was wrong on two counts. Firstly despite the hype, Professor Thapar’s (et al) study did not establish a genetic basis for ADHD. Secondly and most importantly, if a genetic basis of ADHD is eventually established it will validate ADHD as a ‘genetic difference’ not a ‘genetic disease’.

Over-hyped study did not establish a genetic basis for ADHD

The study that Professor Thapar claimed established that ADHD is a ‘genetic disease’ involved the comparison of the genetic codes of 366 children ‘with ADHD’ with that of 1047 ‘non-ADHD’ control children. Researchers found 13.9% (51) of ADHD children with ADHD had short lengths of their genetic code that were either duplicated or missing. This compared with 7.4% (78) of the ‘control children’.^[2] In other words the vast majority of ‘ADHD children’ (86%) did not have the hypothesised ‘ADHD genes’ and some ‘non-ADHD children’ did.

Even the 13.9% to 7.4% difference is dubious as there appears to be significant differences between the average IQ’s of the two groups. The average recorded IQ of the 366 children ‘with ADHD’ was 86, fourteen points below the general population average of 100. Whilst the IQ of the 1047 ‘non ADHD children’ was not specified, presumably they were as intelligent as the general population (average IQ of 100).

Furthermore when 33 intellectually impaired ‘ADHD children’ (IQ lower than 70) were excluded from the ADHD cohort only 11% of the remaining 333 had the hypothesised ADHD genetic abnormality.^[3] Even with the intellectually impaired children removed the average IQ (89) of the 333 remaining in the ADHD group was significantly lower than the control group (presumed to be 100).^[4]

This evidence is more suggestive of a relationship between the identified genetic abnormality and intellectual disadvantage than it is of ADHD. In fact the authors of the study acknowledged the likely association between intellectual disability and the genetic abnormality identified but defended their comparisons of populations with a low average IQ (86 and 89) with a normal control population.

The study should have compared like with like. That is, the ‘ADHD’ cohort of children should have had the same average IQ as the ‘non-ADHD’ cohort of children. However the reason offered by the authors for not comparing like with like was convenience not science; being that they did not have IQ measures for the control group.^[5] The authors offered the feeble explanation that the low average IQ of the ADHD cohort was of no consequence as the non-ADHD cohort included ‘individuals spanning a wide IQ spectrum which presumably includes those with a lower IQ.’^[6]

Genetic Difference is not Genetic Disease

Some critics of ADHD, including American neurologist Fred Baughman, argue ADHD is a fraud because there is no robust scientific evidence of genetic or physiological difference that are the prime characteristic of disease.^[7] I agree with Dr Baughman that there is no such robust evidence although studies of twins have hinted at genetic differences. However, I believe it is possible, and even in time likely, that some common genetic patterns may be identified amongst many children diagnosed ADHD. (Note; care would need to be taken in reaching these conclusions as there is evidence that ADHD drugs rather than the ‘disorder’ may be responsible for causing chromosomal damage.^[8])

At its essence ADHD is just a loose collection of behaviours, with children diagnosed being on average less attentive and/or more impulsive/hyperactive than their peers. Finding a genetic basis for ADHD would therefore mean finding a genetic basis for inattentive and/or impulsive/hyperactive behavior. And it is entirely reasonable to think behavior is a combination of nature and nurture. However, conceding ADHD may be in part a ‘genetic difference’ is vastly different from accepting it could be a ’genetic disease’.  

In 2005 Queensland psychologist Dr Bob Jacobs wrote: ‘Even if researchers found a consistent difference between children who act a certain way (‘ADHD’) and children who don’t, and even if they could somehow prove that the difference caused the behaviours, there is no reason to believe there is any ‘disorder’. There may be physiological differences between people who are right-handed and left-handed, or people who prefer the colour red over the colour blue. But it doesn’t make either group ‘sick’. We know that people have individual physical differences, but it is dangerous ground to say that those differences are a ‘disorder’, just because they are in the minority, or because the cause problems with fitting into society’s rigid structures (like school).’^[9]

It is possible that at some time in the future scientists may identify the role genetics plays in determining individual differences in attentiveness, impulsivity and hyperactivity (and therefore ADHD).  But as Dr Jacob’s points out, the search for ADHD specific differences in genetics, brain structure or any other physiological characteristics, which has so far proven fruitless, is also futile. For even if the search was eventually successful, all it could demonstrate is difference, not disease and difference is not disease.

Much ado about nothing

The media hype around Professor Thapar’s (et al) deeply flawed study is typical of hundreds of similar stories where the ADHD enthusiasts over-reach with claims of new methods of validating, diagnosing or treating ADHD. Time pressured journalists often repeat these over-blown claims without understanding the methodological limitations of these often ADHD industry sponsored and controlled studies.

By the time the hyped claims are subsequently shown to be flawed, or even a complete fabrication, the media caravan has moved on. Unfortunately history tells us that just like Professor Thapar’s claim, the next claim of a genetic research breakthrough, scientific diagnostic procedure or safe wonder drug will be uncritically reported, further fuelling the ADHD Industry. 

[2] Williams, Dr N.M. &  Thapar, Prof. A. (et al) ‘Rare chromosomal deletions and duplications in attention-deficit hyperactivity disorder: a genome-wide analysis’, The Lancet Vol376:9750, 30 September 2010 <http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)61109-9/abstractOriginal Text>

[3] Williams, Dr N.M. &  Thapar, Prof. A. (et al) ‘Rare chromosomal deletions and duplications in attention-deficit hyperactivity disorder: a genome-wide analysis’, The Lancet Vol376:9750, 30 September 2010 <http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)61109-9/abstract>

[4] Note: Whilst there is considerable anecdotal evidence of bright but under-stimulated and bored children being diagnosed with ADHD it could be for the geographical population of this study that having a low IQ increases a child’s chances of being diagnosed with ADHD.

[5] Williams, Dr N.M. &  Thapar, Prof. A. (et al) ‘Structural variations in attention-deficit hyperactivity disorder — Authors’ reply’, The Lancet, Vol377:9763, 29 January 2011 <http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)60121-9/fulltext>, p.378outline goes here

[6] Williams, Dr N.M. &  Thapar, Prof. A. (et al) ‘Structural variations in attention-deficit hyperactivity disorder — Authors’ reply’, The Lancet, Vol377:9763, 29 January 2011 <http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)60121-9/fulltext>, p.378

[7] see Dr Baughman’s website www.adhdfraud.org

[8] ‘Drug Updates: ADHD Drug Methylphenidate Linked to Chromosomal Changes’ Play Attention  <http://playattention.com/attention-deficit/articles/drug-updates-adhd-drug-methylphenidate-linked-to-chromosomal-changes/>

[9] Jacobs, Dr B. ‘Being an Educated Consumer of ‘ADHD’ Research’, Youth Affairs Network of Queensland, 2005.