Attention Deficit Hyperactivity Disorder (ADHD) is influenced by many genetic variants common to this disease, each of which slightly increases the risk, a study reveals.
- The vast majority of genetic variants discovered also have an influence on other mental disorders such as autism, depression and schizophrenia.
- 2 million people in France suffer from ADHD, according to the association HyperSupers TDAH France.
The study is "revolutionary”, wrote the researchers from the University of Aarhus, Denmark. Indeed, thanks to their research published in the journal Nature Genetics, an unprecedented number of common genetic variants have been discovered that increase the risk of Attention Deficit Disorder with or without Hyperactivity (ADHD); a neurodevelopmental disorder.
Some genetic variants increase the risk of ADHD
The term “genetic variants” refers to specific variations in the DNA code – in this specific case, variants that are seen more frequently in people with ADHD than in people without a diagnosis. DNA variations affect, for example, the degree expression of a gene and, subsequently, the quantity of proteins encoded by this gene, explain the authors.
Using advanced statistical models of more than six million genetic variants in 38,691 people with ADHD and 186,843 people without ADHD, the researchers estimated that there are about 7,300 that increase the risk of developing the disorder.
The 27 that they were able to map provide some answers to two questions. Why do some people have ADHD while others do not? And at what point in life or in the womb is the seed of ADHD sown?
“ADHD should be considered a developmental disorder of the brain”
According to the researchers, the genes involved in ADHD are expressed in several brain tissues, even at the embryonic stage: “This underscores the fact that ADHD should be considered a developmental disorder of the brain and is most likely influenced by genes that have a major impact on early brain development.“, said the first author of the study, Professor Ditte Demontis of the Department of Biomedicine at Aarhus University.
Additionally, researchers have found that genetic factors that increase ADHD risk particularly affect genes that are expressed in dopaminergic neurons, which synthesize dopamine (the happiness hormone) and use it as a neurotransmitter.
ADHD symptoms worsen based on genetic mutations
“This is interesting because dopamine plays a role in relation to the reward response in the brain, and because a frequently used form of ADHD medication works by increasing the concentration of dopamine in different regions of the brain. Our results indicate that the dopamine imbalance in the brains of people with ADHD is partly attributable to genetic risk factors.“, explains Ditte Demontis.
This discovery also detected that a high presence of ADHD risk variants in an individual’s genome is associated with reduced reading and numeracy skills, reduced attention and reduced short-term memory. .