Studies estimate the mean heritability of ADHD to be 76%, indicating that ADHD is one of the most heritable psychiatric disorders.
Hypotheses exist that include in utero exposures to toxic substances, food additives or colorings, or allergic causes. However, diet, especially sugar, is not a cause of ADHD. How much of a role family environment has in the pathogenesis of ADHD is unclear, but it certainly may exacerbate symptoms.
ADHD is associated with a number of other clinical diagnoses. Studies have demonstrated that many individuals have both ADHD and antisocial personality disorder. These individuals are at higher risk for self-injurious behaviors. ADHD is also linked to addictive behavior.
In children, ADHD is three to five times more common in boys than in girls. Some studies report an incidence ratio of as high as 5:1. The predominantly inattentive type of ADHD is found more commonly in girls than in boys.
For more on the presentation of ADHD, read here.
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Cite this: Glen L Xiong, Stephen Soreff. Fast Five Quiz: Do You Know the Signs, Symptoms, and Best Practices for Attention-Deficit/Hyperactivity Disorder? - Medscape - Sep 14, 2015.