Medical News Today recently ran a headline stating "ADHD Is A Genetic Neurodevelopmental Disorder, Scientists Reveal." They drew this headline from a recent study published in The Lancet, which analyzed the DNA of 366 children diagnosed with ADHD against a much larger control group. The study in The Lancet concluded that 15% of the ADHD sample had chunks of DNA missing or duplicated compared to 7% of the control group. This is a significant result, suggesting a probable genetic predisposition for some children with problems with inattention and impulsivity.
But it hardly justifies the headline nor the statement by Professor Anita Thapar, lead investigator of the study:
"Now we can say with confidence that ADHD is a genetic disease and that the brains of children with this condition develop differently to those of other children."
In fact, if one looks closely at the numbers, a more accurate headline begins to take shape: "85% of ADHD cases found to have no genetic basis." Admittedly, this is an over-simplification, as there may be other, hitherto undiscovered genetic markers implicated in impulsivity and inattention. However, if you consider the fact that the investigators in most studies of ADHD are more rigorous in their election process than clinicians, who often diagnose and prescribe stimulants for "subclinical" cases, the percentage of nongenetic impulsive/inattentive behavior is probably far higher than 85%. Not to mention that the headline and Professor Anita Thapar's conclusion ignore the complex interaction between environment and heredity at the heart of nearly all psychological diagnoses. The fact that 7% of the "normal" population have the same genetic markers and no diagnostically significant symptoms suggests that DNA abnormalities are just pieces in a larger puzzle.
The problem is that spin in medical journals has a huge effect on clinical practice. You can be sure that pharmaceutical reps have incorporated the headlines, rather than the numbers, into their talking points. And how many pediatricians and psychiatrists look past these headlines to the nuanced results? CHADD, the largest ADHD patient advocacy group (largely funded by drug companies), now states in its website, without referencing specific studies:
"There is little question that heredity makes the largest contribution to the expression of [ADHD] in the population. "
The belief that ADHD is determined by genes invariably means that a child will be treated with stimulant medication rather than therapy. You don't use words against a brain abnormality. The numbers bear this out. Global sales of ADHD drugs increase 8% year on year and are forecast to reach $4.3 billion by 2012. For the parent who consults with a doctor about a child's impulsive behavior, caveat emptor.