Attention Deficit/Hyperactivity Disorder (ADHD)
Demographics, Developmental Course, And Etiology
ADHD occurs in about 3 to 7 percent of the general population. As is the case with nearly all developmental disorders, it is more common in boys than girls, with a male to female ratio of about 3:1 in community settings and even higher in clinical settings. An exception is that individuals displaying the Inattentive type of ADHD—formerly termed attention deficit disorder without hyperactivity and distinguished by inattention but without noteworthy hyperactivity and impulsivity—has a male to female ratio closer to 1.5:1 or 2:1.
Longitudinal studies demonstrate that ADHD almost always persists into adolescence, and in a plurality of cases impairment lasts into adulthood (Mannuzza and Klein 1999). Although the motor overactivity per se dissipates with time, inattention, disorganization, impulsivity, and academic and social difficulties are likely to persist well beyond childhood.
Regarding etiology, ADHD is one of the most heritable conditions in all of psychopathology. Seventy to 80 percent of the individual differences in ADHD-related symptoms are attributed to genetic rather than environmental factors. Thus, ADHD's genetic liability is higher than that for depression or schizophrenia, and roughly equal to that for bipolar disorder or autistic disorder (Tannock 1998). Although ADHD is not a simple, single-gene condition, recent discoveries at the molecular genetic level implicate genes related to dopamine neurotransmission. Note that, because ADHD persists throughout development and because it is strongly familial, a high proportion (30–40%) of the biological parents of children with ADHD will have clinically significant symptoms themselves, whether or not formally diagnosed. Thus, the new generation often suffers from both genetic and psychosocial risk, the latter related to being raised by parents who are themselves not fully self-regulated.
Other biological (but non-genetic) risk factors for ADHD include low birthweight, several types of prenatal and perinatal complications, and maternal use of substances such as nicotine, alcohol, or illicit drugs during pregnancy (Tannock 1998). Although these risk factors are not inevitable causes of ADHD—and most cases of ADHD do not show associations with these risks—they do play a role in many individuals with the disorder. Overall, ADHD has strong psychobiological origins.
Can ineffective parenting cause ADHD? Most experts say no, because (a) many discordant family characteristics appear to result from (rather than predispose to) having a child with the difficult behavioral pattern demarcated by ADHD and (b) children with ADHD do not show higher than expected rates of insecure attachment in infancy and toddlerhood (Hinshaw 1999). Nevertheless, there some evidence for family "causation" with respect to children from impoverished backgrounds: In a high-risk sample, Elizabeth Carlson and colleagues (1995) found that unresponsive and overly stimulating parenting styles during the first two years of life could be used to predict ADHD-related symptomatology years later, over and above indicators of early temperament and biological dysfunction. In most cases, however, parenting may serve to accentuate or exacerbate difficult temperament or other signs of early biological risk.
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