A pair of genes to suit every occasion?

Hyperactive children are typically underachievers. Estimates vary but most researchers and teachers agree that children with Attention-Deficit / Hyperactivity Disorder (ADHD) often have significant learning problems, and research tells us that there is a correlation between early identification of hyperactivity and levels of academic achievement ten years later.

All well and good – but which way does the relationship operate? Does poor academic achievement lead to hyperactivity (children fail to grasp school work and subsequently act out from boredom or frustration)? Or does hyperactivity lead to poor academic achievement (children cannot concentrate and engage with school work and therefore under-perform)?

Behavioral genetics suggests a third possibility: that the relationship between academic achievement and hyperactivity is genetically mediated. Research indicates that hyperactivity has a strong genetic component; academic performance is also governed to a considerable degree by inheritance (recent evidence suggests that genetic factors explain about 50% of the variance in academic outcomes). So perhaps there is a genetic basis for linking the two.

But wait: even strong proponents of the importance of genetics caution that genes cannot explain all of the variance in child outcomes. There is always interplay between genes and the environment (known as ‘g x e’). The better question, then, is how strong is the interaction?

A study by Kimberly J. Saudino and Robert Plomin is getting to grips with this tangle of important issues. It investigates the possibility of a shared genetic component for hyperactivity and academic achievement and the degree to which the environment plays a part, by following the progress of nearly 1,000 monozygotic (identical) and 1,000 dizygotic (non-identical) twins from 18 months.

Their work is an aspect of the Twins Early Development Study (TEDS), which is keeping track of all twins born in England and Wales between 1994 to 1996. The TEDS analysis focused on seven-year-olds. Hyperactivity was assessed by the Strengths and Difficulties Questionnaire (SDQ; Goodman, 1997) and academic achievement by children’s key stage one results. Children’s intelligence was also taken into account.

The TEDS findings refute the idea that poor academic achievement leads to hyperactivity. But they provide stronger evidence for the alternative hypothesis – that hyperactivity causes poor school performance – confirming previous research that hyperactive children have difficulties processing information. The suggestion is that their executive functioning may be disrupted resulting in poor attention span, poor organizational skills and difficulty with complex instructions.

So the bigger study begins to explain how hyperactivity may cause disruption to children’s ability to learn, but it does not explain why – and this is where Saudino and Plomin’s results come in. They find that approximately 40-50% of the genetic basis for hyperactivity overlaps with that of academic achievement.

But what about the other 50-60% of the variance?

Another study by DiLalla and Mullineaux, in press with the Journal of School Psychology, which uses the same TEDS cohort but focuses on four-year-old twins, fits another intriguing piece into the puzzle.

Exploiting the fact that not all identical twins were in the same school classes, they were able to rely on the stability of the genetic component and so concentrate on the effects of a shared or non-shared environment. It turned out that the mental health outcomes of separated twins differed from those of the twins in the same class.

So, while the Saudino and Plomin study suggests that genetics are important, DiLalla and Mullineaux tell us that genes are not everything and that the environment plays a vital role.

Where do we go from here? For the foreseeable future, altering children’s genes in an attempt to improve mental health is clearly going to be much more difficult than experimenting with the environment. And the value of making simple changes in the classroom is already evident from recent program trials.

For example, Christine Merrell and Peter Tymms from The Curriculum, Evaluation and Management Centre [1] at Durham University have compared the benefits of screening for hyperactive children, providing teachers with simple techniques to help hyperactive children in their classes, and making available a combination of both.

Based on a randomized control trial involving over 70,000 children from over 2,000 schools in the UK, they found that screening on its own actually had a negative impact, but using simple instructional techniques for teachers improved behavior and academic performance [see also Repairing children's mental health – through thick and thin [2].

No doubt the whole story will turn out to be even more complex, but the underlying message is clear: the classroom environment influences behavior and academic performance and this can be changed for the better. What is needed is more adventurous innovation and more evaluation.

references
Saudino Kimberly J and Plomin R, "Why are Hyperactivity and Academic Achievement Related?" Child Development, 2007, 78, 3, pp972–986

DiLalla Lisabeth F and Mullineaux Paula Y, "The effect of classroom environment on problem behaviors: A twin study" in press, the Journal of School Psychology

Tymms P and Merrell C, "The impact of screening and advice on inattentive, hyperactive and impulsive children", European Journal of Special Needs Education. 21, 3, pp321-337