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Disclaimer: This article contains descriptions and mentions of eating disorders and mental health ailments
Demontis, D., Walters, R.K., Martin, J. et al. Discovery of the first genome-wide significant risk loci for attention deficit/hyperactivity disorder. Nat Genet 51, 63–75 (2019). https://doi.org/10.1038/s41588-018-0269-7
Attention-Deficit Hyperactive Disorder, or ADHD, is a neurodevelopmental condition that affects approximately 8.4% of children worldwide. Some common symptoms include a severe inability to pay attention to a given task, impulsive and sometimes reckless behaviour, trouble managing time, and being unable to finish tasks. This study provides evidence to show that ADHD is caused by inherited genes found on specific loci (a fixed position on a chromosome where a particular gene is located). A chromosome is a structure of DNA that contains part of, or all the genetic material of an organism.
A genome is the complete set of genes present in each cell. GWAS (genome-wide association studies) were conducted on people diagnosed with ADHD, as well as people that did not have it. A genome-wide association study is a research method used to identify genetic variants that can increase the risk of a particular condition. After GWAS, it was concluded that 304 specific variants of genes over 12 loci met the criteria for genome-wide significance. This supports the theory that ADHD is defined by heritable traits passed down over generations.
This conclusion also implies that ADHD is polygenic, i.e. its characteristics are controlled by two or more inherited genes. To test this further, PRS tests were applied to all participants. The PRS (polygenic risk score) measures an individual’s risk of a certain condition based on the influence of their genetic variants. The individuals with ADHD had a significantly higher PRS score compared to the controls (individuals without ADHD). This further illustrates that the condition is genetic and that the offspring of a person with ADHD is likely to inherit it from their parents with the specific genes that increase the risk of ADHD.
These specific genes whose traits combine to form ADHD are found on a few select chromosomes. For example, the forkhead box protein (FOXP2) gene that controls speech and language is located on chromosome 7, causing people with ADHD to have problems with language skills or comorbid learning disabilities like dyslexia. Primary school students with subpar language skills are often inattentive and hyperactive as well. Chromosome 10 has the gene SORCS3 whose malfunction can lead to depression, often comorbid with ADHD. SORCS3 controls neuronal plasticity, which is the ability of the brain to rewire itself based on changes in its environment. Chromosome 5 is linked to the LINC00461 gene which adversely affects educational uptake in ADHD. It also has the MEF2C-AS1 gene, which leads to schizophrenia and Alzheimer’s disease, also associated commonly with ADHD.
There are 43 phenotypes (characteristics that result due to genes) that especially overlap with ADHD, causing them to be prone to other psychological conditions, such as an addiction to nicotine, insomnia, anorexia and major depressive disorder. An individual with ADHD may smoke to ‘quiet’ their brain, as it provides the same psychostimulant effect that common ADHD medications provide. Sudden hyperactivity and hyperfocus on tasks may make individuals with ADHD lose sleep, leading to insomnia. Individuals affected by ADHD may develop anorexia due to their ADHD brain’s impaired self-regulation abilities and their dysfunctional task-and-reward system – leading them to ‘reward’ themselves with food after deliberately starving themselves. This is closely linked to major depressive disorder; individuals with ADHD may develop it if they find managing their symptoms particularly difficult, leading to lowered self-esteem and deep-seated feelings of hopelessness. Often, individuals who are already diagnosed with any of these conditions may also have ADHD which goes unnoticed, as they are so closely linked.
However, the study was limited as it mostly tested European and East Asian individuals, so testing people of more ethnicities could have improved the study. The individuals with ADHD, or those who had higher risk factors for it, could have their family backgrounds examined to see if they could have inherited the particular genes from any members of their immediate family. Moreover, the study is valuable because it counters the idea that ADHD is caused due to one’s environment.
In conclusion, the genome-wide study illustrates that ADHD is a highly heritable condition caused by certain genes located on specific chromosomes. The effects of each gene combine to cause the biological symptoms associated with the condition, and the presence of these genes over generations of a family increases its risk.
Read more about ADHD and possible treatments here:
Summarised by Daya Ravi
Works cited:
Poor, Armeen, and Keath Low. “Why People with ADHD Are More Likely to Smoke Cigarettes.” Verywell Mind, 18 May 2022, www.verywellmind.com/adhd-and-smoking-20773.
Powell, Victoria, et al. “ADHD in Adults with Recurrent Depression.” Journal of Affective Disorders, vol. 295, no. 1011, Dec. 2021, pp. 1153–1160, https://doi.org/10.1016/j.jad.2021.09.010.
Reinblatt, Shauna P. “Are Eating Disorders Related to Attention Deficit/Hyperactivity Disorder?” Current Treatment Options in Psychiatry, vol. 2, no. 4, 9 Oct. 2015, pp. 402–412, https://doi.org/10.1007/s40501-015-0060-7.
Carolyn M. Hutter, Ph.D. “Genome-Wide Association Studies (GWAS).” National Human Genome Research Institute, 2019, http://www.genome.gov/genetics-glossary/Genome-Wide-Association-Studies.
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