Description

• Symptoms include difficulty concentrating, impulsivity, and hyperactivity/overactivity. Impairment in executive functioning and emotional dysregulation are common features.
• The three main types of ADHD are (i) hyperactivity-impulsivity predominant, (ii) inattentive predominant, and (iii) combined. The combined type is the most common, followed by the inattentive and hyperactive types.

Epidemiology

Prevalence
ADHD affects approximately 4.4–5.2% of adults between 18 and 44 years of age (1). ADHD is more common in men than women, who are less likely to be referred for assessment and more likely to be undiagnosed or misdiagnosed.

Etiology and Pathophysiology

Genetics

• ADHD appears to have a genetic component, with heritability of approximately 0.8, suggesting that genetic factors would account for about 65% of phenotypic variance.
• First-degree relatives of persons with ADHD reported to have 4 to 5 times greater risk than general population.

Risk Factors

• The risk of ADHD is increased among offsprings of mothers who smoked or had obesity and diabetes during pregnancy. Risk is also increased in those who had lead exposure in childhood. It is unknown whether these associations are causal.
• Premature birth; very low birth weight; and extreme neglect, abuse, or social deprivation also increase the risk as do certain infections during pregnancy, at birth, and in early childhood.
• Other factors associated with increased risk for ADHD include neurodevelopmental disorders including autism spectrum disorder and learning disabilities.

Commonly Associated Conditions

• Substance use and substance abuse disorders
• Mood and anxiety disorders
• Intellectual disabilities
• Obsessive-compulsive disorder (OCD)
• Tic disorders
• Delayed sleep-wake phase disorder