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Attention Deficit Hyperactivity Disorder - Causes
Last reviewed: 04.07.2025
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Attention Deficit Hyperactivity Disorder - Causes
The cause of ADHD remains unknown. Similar clinical manifestations are seen in fragile X syndrome, fetal alcohol syndrome, very low birth weight infants, and very rare hereditary thyroid disorders; however, these conditions account for only a small proportion of ADHD cases. The search for the causes of ADHD is being conducted in various directions, using genetic, neurochemical, structural and functional neuroimaging studies, etc. For example, patients with ADHD have a decreased size of the anterior corpus callosum. Single-photon emission computed tomography (SPECT) has revealed focal hypoperfusion in the striatum and hyperperfusion in the sensory and sensorimotor cortex. Genealogical studies conducted over the past 25 years have shown that ADHD and its comorbid conditions tend to cluster in certain families, with the odds of inheriting ADHD ranging from 0.55 to 0.92. A number of studies have found decreased dopamine and norepinephrine turnover in the brain, but the neurochemistry of the brain is extremely complex, and attempts to link ADHD to dysfunction of any one neurotransmitter system are oversimplified. Psychosocial and environmental factors (e.g., food additives or excess sugar intake) do not appear to play a major role in the etiology of ADHD.
Attention Deficit Hyperactivity Disorder - Epidemiology
Sociological studies confirm that attention deficit hyperactivity disorder is the most common mental disorder in childhood and adolescence, occurring in 5-10% of elementary school children. In the United States, more than 7% of school-age children are treated with psychostimulants (primarily methylphenidate). Psychostimulants are taken by almost 25% of children in special education programs. Attention deficit hyperactivity disorder is more common in boys, with the ratio being higher in clinical studies (9:1) than in epidemiological studies (4:1). This difference may be partly due to the fact that boys are more often referred to a doctor, or to the specificity of symptoms of attention deficit hyperactivity disorder in individuals of different sexes.
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