From Genes to Behavior: A Comprehensive Review of ADHD and Its Triggers Across Multiple Factors

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that affects millions of individuals worldwide. ADHD is characterised by inattention, impulsivity, and hyperactivity, which research suggests are linked to structural differences in key brain regions. These areas include the prefrontal cortex, basal ganglia, and cerebellum, which play important roles in managing executive function and motor control. Alongside ADHD is another recurring neurodevelopmental disorder known as Dyslexia, that affects reading and phonological processing, with disruptions observed in left hemisphere regions, particularly the occipito-temporal regions, which are critical for reading. Although ADHD and dyslexia are different in terms of their symptoms and the brain areas affected, researchers are investigating their potential genetic connections. While there is limited evidence to show a direct overlap in genetic causes between the two disorders, some studies suggest similarities in brain structure. For instance, functional imaging techniques, like functional magnetic resonance imaging (fMRI) and single photon emission computed tomography (SPECT), have revealed that in ADHD, fMRI studies have shown decreased activation in the prefrontal cortex (PFC) during tasks that require focus and self-control, which may help explain the attention and impulse-control challenges. Similarly, in dyslexia during reading tasks, fMRI highlighted lower activity linked to reading difficulties. ADHD also shows a strong genetic component, with heritability linked to genes like the dopamine receptor D4 (DRD4) and dopamine transporter gene (DAT1), which play roles in the disorder’s development. In addition environmental factors also affect ADHD by modifying gene expression through epigenetics— factors like stress and nutrition influence genes without changing the DNA itself. For example, genes like BDNF (important for brain adaptability) and FoxP2 (related to language and motor skills) are sensitive to environmental changes. Interestingly, these same genes, including DAT1, FoxP2, and DRD4, have also been associated with dyslexia, showing that both genetic and environmental factors may shape the outcomes of both ADHD and dyslexia.