What Causes ADHD?

Among 5 to 9 percent of the school age population is diagnosed to have Attention-Deficit/Hyperactivity Disorder. It is characterized by age-inappropriate inattention, distractibility, increase restlessness, and impulsivity. It commonly occurs in males than in females although in adult cases, frequency occurs on equal proportion. Approximately 2 out 4 percent of adults are believed to have ADHD. This disorder has serious negative effects if not detected and treated immediately however, a lot of adults are remained to be unidentified and left untreated.

The cause and pathogenesis of ADHD have not been completely defined but there are theories stating that ADHD has a biologic basis. One of the best documented causes is the genetic predisposition although specific genetic mechanisms have not been definitively documented. Many studies conducted among families, twins, and adoption reported high heritability. According to some studies, ADHD is associated with dopamine-deficiency which is supported by the fact that most drugs used to manage ADHD acts by increasing the production of dopamine. Two dopamine genes have been found out to have significant relationship with the disorder. However, the two genes do not appear to be responsible for the degree of heritability found in certain studies.

Experiments through Magnetic Resonance Imaging (MRI) also found out that ADHD brains are smaller than controls found in the right side of the frontal area and basal ganglia. This finding explains the impairment in the executive function of children with ADHD. Executive functions has something to do with self-control and commonly deals with the management functions of the brain such as planning, inhibition of impulse, and voluntary direction of attention. However, other brain imaging studies such as Positron Emission Tomography (PET) and electroencephalogram (EEG), do not share the same result with MRI.

Aside from the familial tendency and heredity, a variety of pathophysiologic etiologies are seen to cause the occurrence of ADHD at least in small populations. Some of these include encephalitis, birth trauma, cranial anomalies, low birth weight, fetal alcohol syndrome and head injuries. Recent studies also show the close association of ADHD with heavy metal poisoning, viral exposure, deficiency in various minerals such as zinc, specific essential fatty acid deficiency, food allergies, abnormality and problems with the thyroid gland, and pediatric autoimmune disorders such as group A beta-hemolytic streptococcal infections like tonsillitis, acute glomerulonephritis and rheumatic heart disease. There are also some studies supporting the theory that excessive time spent in front of the television is closely associated with ADHD. Maternal deprivation can also be linked with hyperactivity.

Just like any other neuropsychiatric disorders, stress aggravates the condition. Since what causes ADHD is not yet clearly specified, various studies conclude that the development of clinical symptoms in ADHD is likely attributed to the interaction of genetic tendency with environment, both physically/chemically and psychosocially.