I am grateful to Dr Double for giving me the opportunity to cite more references than are allowed in a debate; but the biological basis of hyperactivity is one of the most researched questions in psychiatry and a letter cannot do justice to it. The chapter I cited previously gives references, and interested readers might also like to consult the recent reviews cited below.

The best-established findings are probably the associations with DNA variations in genes coding for the dopamine receptor (Reference DiMaio, Grizenko and JooberDiMaio et al, 2003) and dopamine transporter, and neuroimaging findings of altered brain structures including frontal lobe and striatum.

Castellanos et al (Reference Castellanos, Lee and Sharp2002), for example, report the altered neuroanatomy of ADHD, with the brains of those who have never been medicated being more abnormal than those of children who have received stimulants.

Dr Double extends the debate to the question of the use of medication. A large controlled trial (MTA Collaborative Group, 1999) has shown significant advantages of medication over psychological therapy (although I believe that psychological treatment still has an important place). I should therefore like to emphasise that there are dangers in being too reluctant to diagnose and treat ADHD. Children then often receive more destructive labels. Treatment can restore normal function, so it seems to me unacceptable to withhold its benefits from individual children for the sake of a preference for a different form of society.