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The Role of Genes and Environment in Attention Problems Throughout Aging
The Role of Genes and Environment in Attention Problems Throughout Aging
Department of Biological Psychology, VU University, Amsterdam, The Netherlands
First published in Psychiatry Weekly, Volume 7, Issue 24, December 17, 2012
Introduction
Not all adults originally diagnosed with attention deficit/hyperactivity disorder (ADHD) during childhood still meet the full criteria for ADHD by 25 years of age; fifteen percent do, however, and 65% continue to exhibit symptoms, such as having attention problems.1 ADHD therefore demonstrates both change and stability.
A Twin Study of Attention Problems
Dr. Kees-Jan Kan and colleagues2 conducted a retrospective, longitudinal twin study to examine how environmental and genetic factors contribute to change and stability in attention problems. The study was based on data from The Netherlands Twin Registry, which is now in its 25th year. Symptom ratings for attention problems of more than 44,000 child, adolescent, and adult twins were analyzed. For twins up to 12 years of age these symptom ratings were provided by their mothers. Older twins provided self-ratings.
“There isn’t much heritability research in attention problems or ADHD in adults,” says Dr. Kan. “Most of the existing studies are limited. From previous research we may conclude that heritability of ADHD features is lower in adults than in children, which suggests that genetic or environmental effects change somewhere between childhood and adulthood, but this has not been previously investigated.”
To get a developmental view of attention problems, Dr. Kan employed a statistical model that effectively spliced together overlapping repeated measures of the Dutch twin sets registered at birth and the twin sets that were recruited later. This provided a study population ranging from early childhood to late adulthood. (This study evaluated subjects’ mean scores for attention problems. Subjects were not assessed using ADHD diagnostic criteria, and this study did not account for any existing ADHD diagnoses.)
Study Findings
Individual differences in attention problems turned out to be quite stable, especially in adulthood. Stability was due to both genetic and environmental factors. Changes were also present. These were mainly due to environmental factors. Environmental effects appear to accumulate throughout the lifetime and emerge as an important factor in the development of attention problems.
"There was a sharp drop in heritability of attention problems around 12 years of age as a result of an increase in environmental effects."
“We also replicated the finding that heritability of attention problems in adults is lower than in children,” says Dr. Kan. “There was a sharp drop in heritability around 12 years of age as a result of an increase in environmental effects. This change coincided, however, with the switch from mother-ratings to self-ratings, so we suspect the drop does not reflect a real effect but rather a methodological effect. However, this is difficult to sort out and requires more research.”
Prevalence rates of attention problems appeared to change along gender lines during adolescence. At ≤12 years of age, boys had higher ratings of attention problems than girls, whereas young women from 15–30 years of age had higher ratings of attention problems than young men. This reversal also coincided with the switch from mother-report to self-report. “So again it is also quite difficult to disentangle whether this reflects a real change,” says Dr. Kan. “It may be a rater effect, but it may also signify underdetection of attention problems in women, for example.”
Conclusion
Individual differences in attention problems are stable throughout the lifetime, but changes are present as well.
Environmental effects keep accumulating throughout the lifetime and therefore play an important role in the development of attention problems. “Environmental effects clearly affect the prominence and prevalence of attention problems,” says Dr. Kan. “Existing research shows that low birth weight appears to have an association with developing attention problems and ADHD, but, in general, we know very little about other potential environmental factors. Our findings make a case for further research into what kind of environmental factors are at play in attention problems. Greater knowledge of these factors could allow us to recognize and modify them early on, potentially affecting the severity and prevalence of attention problems throughout adulthood.”
DEDICATED TO THE MEMORY OF MARRETJE KAN-BLEKEMOLEN, 1914–2012.
Disclosure: Dr. Kan reports no affiliations with, or financial interests in, any organization that may pose a conflict of interest.
This interview was conducted on November 28, 2012 by Lonnie Stoltzfoos
References:
1. Faraone SV, Biederman J, Mick E. The age-dependent decline of attention deficit hyperactivity disorder: a meta-analysis of follow-up studies. Psychol Med. 2006;36:159-165.
2. Kan KJ, Dolan CV, Nivard MG, et al. Genetic and environmental stability in attention problems across the lifespan: evidence from the Netherlands Twin Register. J Am Acad Child Adolesc Psychiatry. Oct 24, 2012. [Epub ahead of print]