ADHD tends to run in the family. Occasionally it has been mutated. ADHD symptoms normally appear before the age of 7 years. However, they may often have noticed that some children at an early stage. Boys and girls may have different symptoms. ADHD is one of the most common disorders of childhood and adolescence may persist into adulthood. http://www.disorderscentral.com/symptoms-of-attention-deficit-disorder.html