ADHD is characterized by deficits in neurocognitive processes known as executive functions, which include processes that are important for regulating attention and behavior, such as attentional control, inhibitory control, cognitive flexibility, and planning. ADHD stems from multiple causes, including a strong genetic component. Genetics appears to be the principal cause of ADHD, likely accounting for up to approximately 75% of all cases. In a smaller percentage of cases, ADHD may arise from early brain injuries or other disruptions to brain development, such as pregnancy or birth complications. Research does not support the claim that ADHD is a result of food additives, preservatives, or sugar.