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A new analysis of genetic data suggests that individuals with a genetic predisposition for attention-deficit/hyperactivity disorder (ADHD) or autism spectrum disorder may also have a heightened risk for specific heart conditions. The research, which synthesized the results of 14 different studies, points to potential causal links between these neurodevelopmental conditions and cardiovascular health, according to the paper published in the journal Cells.
ADHD and autism spectrum disorder are both considered neurodevelopmental conditions. This means they typically appear early in a person’s development and are associated with how the brain grows and functions. ADHD often involves patterns of inattention, hyperactivity, and impulsivity. Autism spectrum disorder is characterized by differences in social communication and interaction, along with restricted or repetitive behaviors and interests. For many years, doctors and researchers have observed that people with these conditions seem to experience higher rates of cardiovascular diseases, but the reason for this association has been unclear.
Previous studies showing this link were mostly observational. They could identify a correlation, for instance, that adults with ADHD have a 20 percent prevalence of cardiovascular disease. They could not, however, prove that one condition causes the other. The relationship might be explained by other factors, known as confounders. For example, lifestyle habits, stress levels, or the side effects of medications could contribute to heart problems, making it difficult to isolate the direct impact of the neurodevelopmental condition itself.
To get closer to understanding causality, researchers led by Piotr Ryszkiewicz at the Medical University of Białystok in Poland conducted a new type of analysis. Their goal was to examine whether the genetic factors that increase the risk for these neurodevelopmental conditions also directly increase the risk for heart disease.
The researchers conducted a systematic review and meta-analysis of studies that used a method called Mendelian randomization. This technique leverages genetic information to investigate causal relationships between a risk factor and a health outcome. The method is based on the principle that genetic variants are randomly passed down from parents to their offspring, much like participants in a clinical trial are randomly assigned to different groups.
By using genetic variants that are known to be associated with a specific condition, like ADHD, scientists can see if those same variants are also associated with an outcome, such as heart failure. If a connection is found, it provides stronger evidence of a causal link, because the genetic makeup of a person is not influenced by lifestyle or other environmental factors.
Ryszkiewicz and his colleagues searched three major scientific databases for all existing Mendelian randomization studies that explored the links between ADHD, autism spectrum disorder, and various cardiovascular diseases. They identified 14 studies that met their criteria. The team then extracted the data from these studies and evaluated their methodological quality to ensure the findings were reliable. They analyzed the data in two directions: first, looking at whether genetic liability for a neurodevelopmental condition affected the risk of heart disease, and second, whether genetic liability for heart disease affected the risk of a neurodevelopmental condition.
The combined analysis revealed several significant genetic connections. A genetic predisposition for ADHD was linked to an increased risk of developing coronary artery disease, heart failure, and several forms of stroke. Specifically, the data pointed to a higher likelihood of any stroke, ischemic stroke, and large-artery atherosclerotic stroke among individuals with the genetic markers for ADHD. This suggests that the biological pathways associated with ADHD may directly contribute to the development of these serious cardiovascular problems.
The findings for autism spectrum disorder showed a different but also concerning pattern. A genetic predisposition for autism spectrum disorder was associated with a higher probability of developing atrial fibrillation, a type of irregular heartbeat, and heart failure. The analysis did not find a genetic connection between autism spectrum disorder and stroke or coronary artery disease.
When the researchers examined the relationship in the other direction, they found one notable link. A genetic liability for atrial fibrillation was associated with an elevated risk of developing ADHD. The analysis did not find that hypertension, or high blood pressure, had a genetic association with either ADHD or autism spectrum disorder.
The authors of the paper noted some limitations to their work. The number of studies available for analysis was small for some of the specific comparisons, which means some conclusions should be interpreted with caution until more research is done. Another significant limitation is that most of the genetic data came from studies of individuals of European ancestry. This makes it uncertain whether the findings can be generalized to people from other ethnic backgrounds. Additionally, many of the analyzed studies did not conduct power calculations, which are used to determine if a study is large enough to detect a real effect.
Future research should aim to untangle the specific biological mechanisms that connect the genes for these neurodevelopmental conditions to cardiovascular health. Understanding these pathways could lead to better prevention and treatment strategies.
The current findings suggest that clinicians should consider cardiovascular risk assessment as part of the routine care for individuals diagnosed with ADHD and autism spectrum disorder. Early monitoring and intervention related to lifestyle factors like diet and exercise could play an important part in managing the long-term health of people with these conditions. The research also highlights the need for more studies to investigate these bidirectional relationships, especially how specific types of cardiovascular disease might influence the risk of developing neurodevelopmental conditions.
The study, “Evaluating the Causal Effects of ADHD and Autism on Cardiovascular Diseases and Vice Versa: A Systematic Review and Meta-Analysis of Mendelian Randomization Studies,” was authored by Piotr Ryszkiewicz, Barbara Malinowska, and Magdalena Jasińska-Stroschein.