The link between ADHD and dementia across generations
A large study conducted at the Karolinska Institutet in Sweden demonstrates a link between ADHD (Attention-Deficit/Hyperactivity Disorder), dementia, and neurological developmental disorders in a multi-generation study.
The study reveals that parents and grandparents of individuals with ADHD have an increased risk of developing AD (Alzheimer’s disease), a type of dementia, in contrast with relatives of those persons who have no history of the disorder.
Additional correlations exist between aunts and uncles of individuals with ADHD. These relatives have an increased risk of developing AD, but though their risk remains elevated, the onset of AD is less likely.
The diagnosis of ADHD-related generational dementia is relatively new and, only a small number of often-conflicting studies exist.
ADHD is a developmental disorder of the nervous system characterized by poor attention span, impaired impulse control, and hyperactivity. It affects an estimated 8.4% of children globally and often persists into adulthood, affecting roughly 3% of adults worldwide.
Alzheimer’s disease is a degenerative neurological disease characterized by an age-related and progressive decline in both cognitive function and the ability for independent living.
The study
Researchers in Sweden conducted a preliminary study to explore the relationship between ADHD with AD and any type of dementia across generations. They observed that the relatives of individuals with ADHD had an increased risk of developing AD (or other types of dementia) compared to those without ADHD.
The authors of this study searched titles and abstracts indexed on PubMed and discovered that few studies with a limited sample size had investigated the association between ADHD and AD. The findings of these studies are inconsistent.
The study included more than two million people born in Sweden between 1980 and 2001. Of these, approximately 3.2 % were diagnosed with ADHD.
The individuals were linked to more than five million biological relatives using national registries. The relatives in the study included parents, grandparents, and aunts and uncles.
The variables
There are potential genetic and environmental contributions that link AD and other types of dementia with ADHD, according to Dr. Le Zhang, an Assistant Professor in the Department of Neurology at Yale School of Medicine and primary author of the study.
Dr. Zhang’s research focuses on neurodegenerative diseases that include Alzheimer’s disease. Her Ph.D. in Molecular Biology and Biochemistry from the University of Hong Kong and her prior research as a fellow at Harvard Medical School enabled her to study complex degenerative neurological diseases at molecular and genetic levels.
One study’s finding suggests that the same genetic variants may exist in both AD and ADHD. It is also possible that more rare genetic variants contribute to both traits. However, another finding failed to detect any genetic variables common to the AD and ADHD groups.
A contributing variable that may influence the development of early-onset dementia in family members may be the direct effect of ADHD behavior on those family members.
Previous studies show that parents of children with ADHD may experience intense psychological stress that could be a contributing factor, although there is no direct evidence for this. Although this variable could contribute to the increased incidence of AD in parents, it most likely doesn’t correlate with the association in more distant relatives.
An additional finding between the ADHD and AD-related groups is possibly the effect of socioeconomic status within the family as a unit and the stressors it may present.
Another study shows that histamine plays a role in neuronal regulation and is responsible for the development of multiple nervous system disorders that include Alzheimer’s disease and possibly ADHD.
There is an association between ADHD in both children and adults with being obese or overweight. This fact suggests a possible link between midlife obesity and the likelihood of dementia in later life.
The findings
The results revealed that parents of individuals with ADHD had a 34% higher risk of developing AD and that mothers had a slightly higher chance than fathers. The findings also correlated a higher incidence of early- versus late-onset Alzheimer’s disease in these parents.
The study revealed the association between AD- and ADHD-affected groups to be lower for second-degree relatives. These included grandparents, aunts, and uncles.
Grandparents of those affected by ADHD had a 10 percent increased risk of developing early-onset dementia compared to those without relatives with ADHD. The aunts and uncles of relatives with ADHD showed similar findings.
Researchers also observed the prevalence of dementia in people aged 60 and above was approximately 5% to 7% in the general population worldwide. In the population studied here, those percentages rose by 15%.
Final thoughts
The study could not establish a direct cause-and-effect relationship between individuals with ADHD and the development of Alzheimer’s dementia in their parents, grandparents, and aunts or uncles.
“One could imagine that there are undiscovered genetic variants that contribute to both traits, or family-wide environmental risk factors, such as socioeconomic status, that may have an impact on the association,” according to Zhen Chang, a researcher at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet, and the study’s last author. “Another possible explanation is that ADHD increases the risk of physical health conditions, which in turn leads to increased risk of dementia.”
Lastly, the researchers in this study call attention to the importance of studying ADHD and cognitive decline in older age. If a link does exist between them, the scientists propose a search for effective treatments for ADHD to prevent the development of AD or other dementias in individuals with ADHD and their family members.