Clinical spectrum of tic disorders and Tourette syndrome
A growing body of evidence supports the notion that primary tic disorders represent a clinical spectrum, ranging from the mild TTD to Tourette syndrome.
Several studies show that TTD, CMTD, CPTD, and Tourette syndrome are transmitted as inherited traits in the same families, suggesting that they may represent an expression of the same genetic defect.
One problem with the current criteria of Tourette syndrome is that they do not take into account the extensive range of psychopathology and academic problems.
For example, OCD is encountered in at least 50% of patients and is related to the same gene responsible for the expression of tics.
Attention-deficit hyperactivity disorder (ADHD) is also quite frequent (50% to 60%) among patients with TS, but the genetic association between the two conditions is less well understood.
Other behavioral disturbances frequently observed in Tourette syndrome are aggressiveness, anxiety, conduct disorders, depression, learning difficulties, panic attacks, and sleep abnormalities.