ADHD and autism are highly heritable neurodevelopmental conditions. Although they differ from each other in the core symptoms, autism and ADHD have a significant overlap in their underlying genetic causes.
Scientists from Aarhus University have discovered gene variations that raise the probability of getting just one of the diagnoses rather than both. They found five gene variants that are unique to just one of the two diagnoses and seven genetic variants that both ADHD and autism share.
Genetic variations impact how the brain grows and communicates and its nerve cells. It is also surprising that some genetic variations affect the population’s cognitive capabilities. Likewise, scientists identified a gene variant that increases the risk of autism and simultaneously reduces the volume of a specific brain area in people in the general population. In contrast, the complementary variant increases the risk of ADHD and increases the volume of this brain area.
This is the first study that demonstrates- people with both ADHD and autism are double-burdened with a genetic risk of receiving both diagnoses, whereas people who only have one of the diagnoses for the most part only bear the genetic risk variants for this one condition.
Professor Anders Børglum of the Department of Biomedicine at Aarhus University and iPSYCH, Denmark’s largest research project within psychiatry, which is behind the study, said, “This means, for example, that people with both diagnoses have both an equally large load of ADHD genetic factors as people who only have ADHD, and at the same time the same large load of autism genetic factors as people who only have autism. So it makes good biological sense that some people have both diagnoses.”
Scientists analyze large datasets of genetic profiles to understand illnesses and developmental abnormalities better. By doing so, it may be feasible to develop more accurate diagnoses, initiate therapies earlier, and guarantee that each patient receives the best treatment possible.
The study examines genetic variations in the genomes of 34,462 people diagnosed with autism spectrum disorder and/or ADHD and 41,201 control subjects without these diagnoses. For each person, 8.9 million frequently occurring genetic variants have been examined, spread across the entire genome.
Scientists can study the effects of various genetic risk variations by comparing the genetic results with information on the expression of the genes in multiple brain areas and brain cells, such as in the so-called Brain Transcriptome-Wide Association Study (TWAS).
By contrasting the outcomes of the autism/ADHD analyses with those of genetic studies of other mental diseases and general features, such as cognitive functions and the volume of brain areas, the scientists learn more about the importance of the genetic risk variants.
Anders Børglum explains, “The autism diagnosis is typically made before an ADHD diagnosis. So if, for example, the person is also hyperactive and finds it difficult to concentrate, this may well be slightly drowned out by the autism symptoms, and we may not see the ADHD challenges.”
“But if we have a genetic study of a person with an autism diagnosis, and we see a major genetic load of ADHD genetics, then it may be that we should monitor that person more closely. In this way, we can become quicker to spot the development and give the family good tools to handle this diagnosis, too.”
“A few years ago – due to an official diagnosis hierarchy – it was not in principle possible to diagnose ADHD in a person with autism.”
“But now we have shown that people with both diagnoses are double burdened with the genetic risk of both developmental disorders. There is thus a clear biological difference between whether you have both diagnoses or just one. The study is, therefore, a strong biological argument for the revised diagnostic guidelines, e.g., in the American Diagnosis and Classification system for Mental Disorders (DSM-5), where it is now possible for the same person to receive both diagnoses.”
“This is the first step. Here and now, the study is relevant because it helps to create a better understanding of the causes of the two developmental disorders. In the long term, this can form the basis for better diagnostics and treatment.”
- Mattheisen, M., Grove, J., Als, T.D., et al. Identification of shared and differentiating genetic architecture for autism spectrum disorder, attention-deficit hyperactivity disorder and case subgroups. Nat Genet 54, 1470–1478 (2022). DOI: 10.1038/s41588-022-01171-3