Attention-deficit hyperactivity disorder (ADHD) has become a controversial subject in the psychiatric field. In the past few months, a well-publicized study in Lancet Psychiatry generated uproar as prominent researchers criticized the overstated results after finding significant errors in the data. This controversy led to a petition to recall the study. Instead, Lancet Psychiatry published a number of responses to the study and a response of the authors, all of which was reported on here at Mad in America. Many of the researchers who re-analyzed the data found that the conclusion they would actually draw is that ADHD is not a brain disorder and that there is no meaningful difference between the brains of people with an ADHD diagnosis and people without.
For instance, expert researchers stated that “there is no point in conveying that a child with ADHD has a brain disorder.”
And researchers—including ADHD expert Allen Frances, chair of the DSM-IV task force—write that the original conclusion, “is wildly speculative and dangerously misleading at a time when ADHD is already overdiagnosed and overtreated with medication in high-income and middle-income countries.”
At this critical time, an article just published in the International Journal of Qualitative Studies on Health and Well-being examines the way ADHD is taught in academic textbooks. Such textbooks form the basis of educating professionals in the mental health and medical fields, as well as educating future researchers in these fields.
Doctors, therapists, psychiatrists, psychologists, social workers, and social science researchers are all learning about mental health conditions through these textbooks. Thus, it is of vital importance that the textbooks provide the most accurate and up-to-date information about such controversial topics as ADHD.
The researchers, led by Sanne te Meerman at the University of Groningen, Netherlands, examined the most current editions of the textbooks actually being used in courses at major universities in the Netherlands (many of which are English-language books used in many universities around the world).
They found that textbooks routinely fail to present the evidence from molecular genetics studies—evidence that indicates no, or minimal contribution of genetics to ADHD. Instead, textbooks tend to focus on the often-overstated conclusions of behavioral studies—studies that do not actually test for genetic similarities but use behavioral data to infer a genetic component.
Behavioral genetics (also known as “quantitative genetics”), which attempts to determine biological causality without any biological testing, focuses on twin, family, and adoption studies. These studies are often methodologically limited. te Meerman lists many of the possible problems with such studies:
- Researchers and parents are often fully aware which child has the “ADHD” concern and which child does not. Studies have shown that parents often emphasize differences between fraternal twins, and emphasize similarities between identical twins. Studies have also found that adopted twins are often studied after reconnecting with their sibling and emphasizing their similarities. This is known as “rating bias.”
- The studies don’t actually include any genetic testing.
- Twin studies assume that genetics and the environment are two completely separate effects. However, research has consistently shown that genetics and the environment interact. This field is known as “epigenetics” and it invalidates the basic assumptions of behavioral genetics studies.
- The assumption that twins either have a similar environment (if in the same family) or a different environment (if adopted) has also been criticized. Studies have found that twins may be treated very differently, even if the parent is not aware of doing so.
According to te Meerman, despite these methodological limitations, and despite the lack of actual genetic data, some studies claim that up to 90% of ADHD can be explained by genetic factors!
By contrast, molecular genetics focuses instead on searching for the specific genes involved. This involves genetic testing of large groups of people. According to te Meerman:
“Molecular studies into genetics show only small effects for individual genes associated with ADHD. Aggregated they account for less than 10% of explained variance.”
Sanne te Meerman, reached for comment via email, says that:
“Genes by themselves do not determine [what becomes a ‘psychological disorder’]. The ‘suspicious genes’ are almost as common in ‘normal’ people as they are in those diagnosed. Our research strongly suggests that avoiding this inconvenient truth–called the ‘missing heritability problem’–is condoned by many authors as a ‘normal’ way of explaining ADHD.”
That is, textbooks generally ignore the findings of molecular genetics, and instead make overblown claims about the impact of the genetic contribution to ADHD. They avoid the “inconvenient truth” of actual genetic studies and focus instead on the behavioral studies that make assumptions about a genetic component.
An article in Nature explains the “missing heritability problem” in more detail. According to the article, it is not only psychiatry that has this difficulty. In almost every case, researchers have failed to find a large effect of specific genes.
Even molecular genetics can be problematic, according to te Meerman. The studies typically compare large groups of people, with significant overlap. Despite this overlap, statistical methods (averaging the difference between groups) can create the illusion of meaningful differences between the groups.
For instance, the recent controversy in Lancet Psychiatry involved brain volume comparisons between children with the ADHD diagnosis and children without the diagnosis. The two groups almost completely overlapped (researchers stated that 95% of the participants matched the other group’s brain volumes), and children from either group may have had far smaller or far larger brain volumes than children in the other group.
However, because of a slight average difference, the researchers concluded that children with ADHD have smaller brain volumes. However, given the 95% overlap, it continues to be impossible to distinguish between children with ADHD and children without ADHD based on brain volume. If a doctor were presented with a child with smaller-than-average brain volume, that doctor would have to guess completely by chance whether that child had ADHD or not.
te Meerman suggests that academic textbooks (and research publications) should include effect size data, which provides information about how much overlap exists between the two groups (those with the diagnosis and those without). Because there is so much overlap, effect sizes are almost imperceptibly small for the molecular genetics studies.
This serves to counteract the misrepresentation of statistically significant results, which are often not clinically significant or meaningful. Additionally, he suggests that textbooks should include the fact that molecular genetics accounts for–at best–10% of the explanation of ADHD, instead of focusing on methodologically flawed behavioral studies.
te Meerman, S., Batstra, L., Hoekstra, R., & Grietens, H. (2017). Study books on ADHD genetics: balanced or biased? International Journal of Qualitative Studies on Health and Well-being, 12(sup1), 1305590, doi: 10.1080/17482631.2017.1305590 (Abstract)