Animal Models of Tourette’s Syndrome

Abstract

Tics are defined as non-rhythmic, involuntary, and rapid movements or sounds. Approximately 15% of children experience during their growth and development a transient tic condition, without the need of medical treatment, with one or few tics that mostly disappear within less than 1 year. The transient tic condition differs from chronic tic disorder in terms of severity and time course, as in the latter the motor or vocal tics are present for more than 1 year. Tourette’s syndrome (TS), the most severe tic disorder, is a childhood-onset condition consisting of multiple motors and at least one phonic tic for duration longer than 1 year. Tourette’s syndrome was first described by the French neurologist Gilles de la Tourette in 1885. TS was thought to be rare, but recent epidemiological studies have shown prevalence of about 0.3–1%. Tourette’s syndrome is a neuropsychiatric disorder which is characterized by motor and vocal tics. Motor tics are sudden, repetitive, stereotyped movements involving facial twitching, eye blinking, and movements related to head and shoulder, whereas phonic tics are related to sounds generated by moving air with the help of nose, mouth, or throat (e.g., coughing and throat clearing) as well as repeating syllables, words, or phrase. Severity of tics usually peaks between 8 and 12 years of age, but by the end of puberty, many patients show a marked reduction in severity of tics. It has also been reported that less than 20% of children with TS continue to experience a moderate level of destruction of global functioning by the age of 20 years. TS and other psychiatric disorders such as attention-deficit hyperactivity disorder (ADHD), obsessive–compulsive disorder (OCD), and impulse-control disorders (ICDs) are often found to be accompanied by TS and tic symptoms. Only 10–20% of patients suffering from TS are devoid of a co-occurring disorder. Different environmental factors may influence the waxing and waning course of tics. Specifically, this factor involves psychosocial stressors, anxiety, and emotional tension which may exacerbate the expression of tics (Robertson 2008, Hoekstra et al. 2013).