Attention deficit hyperactivity disorder is seen in
ADHD:

Attention Deficit Hyperactivity Disorder.
Difficulty in paying attention, difficulty in controlling behavior and hyperactivity.
Etiology- both genetic and environmental factors. Abnormality in dopamine transporter and thyroid receptor beta genes in some patients.

Three subtypes are known:

Predominantly hyperactive-impulsive
Predominantly inattentive
Combined hyperactive-impulsive and inattentive.

Diagnosis is primarily clinical, using thorough clinical interview of parents and use of behavior rating scales. Physical examination includes direct observation of the child and ruling out chronic systemic illnesses that affect child's attention span.
Insulin resistance
Thyroid hormone resistance
Testosterone deficiency
Calmodulin Deficiency