Attention Deficit Hyperactivity Disorder (ADHD) is a neurobehavioral disorder, which affects up to 3-15% of school children world-wide. ADHD is characterized by hyperactivity, impulsivity, and/or pervasive inattention, and is classified into three types based on the manifestation: the hyperactive-impulsive type, the inattentive type, and the combination type. Hyperactivity is characterized in children by constant motion and activity, while impulsiveness is exemplified by an inability to curb immediate reactions, or to think before acting. Inattentiveness is displayed by children who get easily bored with tasks, and have difficulties in paying deliberate and conscious attention to a job at hand. Although ADHD first appears in childhood, it can continue up to adulthood, although the manifestations may change as age advances. In adults, hyperactivity may be manifested as a state of restlessness and inability to relax, while their impulsive nature may cause personal and professional problems.
ADHD is usually identified only after affected children begin school. Diagnosis of the condition is fairly difficult, considering that features like hyperactivity, distractibility, and inattention are evinced by many healthy children too. Therefore, only a qualified behavioral therapist can make the distinction between a healthy normal child and one affected with ADHD. ADHD may be complicated in a third of affected patients with other conditions including conduct disorder, depression, anxiety disorders, learning disabilities, and Tourette syndrome. Interestingly, ADHD is seen to occur about eight times more frequently in boys than in girls, indicating either a difference in susceptibility between the two sexes, or a failure of diagnosis of the condition in girls. Medications used for treatment are primarily psychostimulants although they do not completely cure the condition, and have been shown to have adverse side effects. Of late, more emphasis is being given to psychotherapy, counseling, special accommodation in the classroom, and family and community support for the efficient management of ADHD.
Although ADHD may develop due to a number of environmental causes, there is a definite genetic component to the condition, evidenced by its familial transmission. Interestingly, in families with natural and adopted children, the condition has been seen to affect only genetically related members. Most research points to ADHD being a complex genetic disorder, with more than two loci involved. In fact, a number of putative loci have been identified, with possible roles in the pathogenesis of ADHD. These include dopamine and dopamine transporter genes, norepinephrine (NE) and epinephrine (EPI) gene, norepinephrine transporter genes, serotonin genes, serotonin transporter genes; GABA genes; and androgen receptor and other genes.