Tic Disorders 83
Prevalence
Tics are common in childhood but transient in most cases. The estimated prevalence of
Tourette’s disorder ranges from 3 to 8 per 1,000 in school-age children. Males are more
commonly affected than females, with the rati o varying from 2:1 to 4:1. A national survey
in the United States estimated 3 per 1,000 for the prevalence of clinically identified cases.
The frequency of identified cases was lower among African Americans and Hispanic
Americans, which may be related to differences in access to care.
Development and Course
Onset of tics is typically between ages 4 and 6 years. Peak severity occurs between ages 10
and 12 years, with a decline in severity during  adolescence. Many adults with tic disorders
experience diminished sympto ms. A small percentage of in dividuals will have persis-
tently severe or worsening symptoms in adulthood.
Tic symptoms manifest similarly in all age groups and across the lifespan. Tics wax and
wane in severity and change in affected muscle groups an d vocalizations over time. As
children get older, they begin to report th eir tics being associated with a premonitory
urge—a somatic sensation that precedes the tic—and a feeling of tension reduction follow-
ing the expression of the tic. Tics associated with a premonitory urge may be experienced
as not completely “involuntary” in that the ur ge and the tic can be resisted. An individual
may also feel the need to perform a tic in a specific way or repeat it until he or she achieves
the feeling that the tic has been done “just right.”
The vulnerability toward developing co-occurring conditions changes as individuals
pass through the age of risk for various co-o ccurring conditions. For example, prepubertal