Possible genetic link between ADHD and dementia

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Published 12 September 2021 at 20.15

Science. A large study at Karolinska Institutet has found a link between ADHD and dementia over generations. The study, published in the journal Alzheimer's & Dementia, shows that parents and grandparents of people with ADHD had a higher risk of dementia than those with children and grandchildren without ADHD.

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– The findings indicate that there is a hereditary and/or environmental link between ADHD and dementia. Now we need further studies to understand the underlying mechanisms, says the study's lead author Le Zhang, a doctoral student at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet.

The number of new ADHD diagnoses has increased sharply in recent decades. Because the diagnosis is relatively new, there are only a few smaller studies that have studied the development of dementia in people with ADHD, and the studies have often shown conflicting results.

In the current study, the researchers wanted to bridge this by examining the extent to which older generations of individuals with ADHD have been diagnosed with dementia. The researchers included more than two million people born in Sweden between 1980 and 2001, of which just over 3.2 percent had an ADHD diagnosis. Using national records, the researchers linked these individuals to over five million biological relatives, including parents, grandparents and parents' siblings, and studied the extent to which these relatives developed dementia.

The researchers found that parents of individuals with ADHD, 34 percent had a higher risk of dementia than parents of people without ADHD. The risk of Alzheimer's disease, the most common type of dementia, was 55 percent higher for parents of individuals with ADHD. It was also more likely that individuals with ADHD had parents with early rather than late dementia onset.

The researchers note that the absolute risk of dementia was small for the parental cohort; only 0.17 percent of the parents were diagnosed with dementia during the follow-up period.

The connection was lower for second-degree relatives of people with ADHD, ie. grandparents and siblings of the parents. For example, grandparents of people with ADHD had a 10 percent increased risk of dementia compared to grandparents of people without ADHD.

The study can not establish a causal relationship, but the researchers present several potential explanations that can be investigated in future studies.

– It is conceivable that there may be hitherto undiscovered gene variants that contribute to both conditions or environmental risk factors, such as socio-economic conditions, that may affect the association. Another possible explanation is that ADHD increases the risk of a number of physical ailments which in turn contributes to an increased risk of dementia, says the study's corresponding author Zheng Chang, researcher at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet, in a statement. p>