dren with ADHD display incr eased slow wave electroenc ephalograms, reduced total
brain volume on magnetic resonance imaging, and possibly a delay in posterior to anterior
cortical maturation, but thes e findings are not diagnostic . In the uncommon cases where
there is a known genetic cause (e.g., Fragile  X syndrome, 22q11 deletion syndrome), the
ADHD presentation should still be diagnosed.
Prevalence
Population surveys sugge st that ADHD occurs in most cultures in about 5% of children