The prevalence and epidemiology of Gilles de la Tourette syndrome

Abstract

The prevalence and epidemiology of Gilles de la Tourette syndrome (GTS) are more complex than was once thought. Until fairly recently, GTS was thought to be a rare and, according to some, a psychogenically mediated disorder. Prevalence depends, at least in part, on the definition of GTS, the type of ascertainment, and epidemiological methods used. However, in dedicated specialist GTS clinics, the majority of patients were noted to have positive family histories of tics or GTS, and large, extended, multiply-affected GTS pedigrees indicated that many family members had undiagnosed tics or GTS: it was therefore realized that GTS was far from uncommon. Seven early epidemiological studies reported that GTS was uncommon or rare for a variety of reasons. More recently, however, two pilot studies and 12 large definitive studies in mainstream school and school-age youngsters in the community, using similar multistage methods, have documented remarkably consistent findings, demonstrating prevalence figures for GTS of between 0.4% and 3.8% for youngsters between the ages of 5 and 18 years. Of the 420 312 young people studied internationally, 3989 (0.949%) were diagnosed as having GTS. It is therefore suggested that a figure of 1% would be appropriate for the overall international GTS prevalence figure. There were however, “outliers” to the figure. For instance, GTS does seem to be substantially rarer in African-American people and has been reported only very rarely in sub-Saharan black African people. GTS is found in all other cultures, although to possibly differing degrees. In all cultures where GTS has been reported, the phenomenology is similar, highlighting the biological underpinnings of the disorder.

Introduction

In order to understand the prevalence and epidemiology of Gilles de la Tourette Syndrome (GTS), one must take the disorder in context, with regard to diagnosis as well as clinical phenomenology, psychopathology, and possible phenotypes, as well as the complex aetiological theories, as they almost certainly all affect the prevalence data.

The generally accepted international diagnostic criteria for GTS, a childhood onset neuropsychiatric disorder, include multiple motor tics and one or more phonic (vocal) tics or noises, lasting longer than a year [1], [2]. The age at onset of GTS ranges from 2 to 21 years, with a mean of 7 years being most commonly reported. The onset of the phonic tics is usually later, many studies reporting it at around 11 years. Both motor and phonic tics can be simple or complex, and characteristic premonitory sensations are common. Typically, the symptoms wax and wane; increase with stress; are suppressible, with rebound after suppression; and are suggestible. Other characteristic but, by no means, ubiquitous symptoms, include echolalia, echopraxia, and palilalia. Coprolalia (inappropriate, involuntary, swearing) is uncommon, occurring in only 10–15% of all GTS patients or about 30% of dedicated GTS clinic patients, and it usually begins at around 15 years [3], [4], [5]. In a study in a pediatric clinic, the case records of 112 patients were examined, and only 8% of the GTS patients had coprolalia [6].

GTS is essentially a chronic tic disorder, although in the majority of cases, there are other associated comorbid conditions [3], [7], [8]. Other recognized tic disorders include (1) chronic motor tic disorder (CMTD) and chronic vocal tic disorder (CVTD), which include single or multiple motor or vocal tics (but not both) present for a year's duration, with the onset before 18 years of age, and (2) transient tic disorder (TTD), which consists of single or multiple motor and/or vocal/phonic tics which last for at least 4 weeks but not longer than 12 months, and start before 18 years of age [1].