Review ArticleSystematic Review and Meta-Analysis of Tourette Syndrome Prevalence; 1986 to 2022
Introduction
Tics refer to a group of nervous developmental disorders that typically manifest during childhood and adolescence and may remain stable over time or fluctuate in intensity or severity. Even though tics are involuntary, some individuals can suppress them during certain periods.1 Tics are repetitive, involuntary, discordant, and sudden movements or sounds that can involve multiple muscle groups and typically appear between the ages four and six years. Tics range from weak and gentle jerks, contractions, and grunting to significant muscle jerks that disrupt social interactions.2,3
The incidence of tics is more prevalent in children than in adults. Consequently, approximately five children of every 10,000 people suffer from tics, whereas only one to two adults are affected.4 The literature in the field indicates that children aged seven to 11 years have the highest prevalence. In addition, Tourette syndrome (TS), the more complete and severe form of the disease, is less prevalent than transient tics. All types of tics are more prevalent in boys than in girls, and the ratio of boys to girls with TS is nearly 3:1.5
Tics were classified into four diagnostic groups in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association, including TS, constant (chronic) motor or vocal tic disorder, provisional (transient) tic disorder, and other specified or unspecified tic disorders. TS is characterized by both motor and vocal tics, whereas chronic motor or vocal tic disorders are distinguished by either motor or vocal tics; they may be simple, such as blinking, shrugging one's shoulders, clearing one's throat, and sniffing, or more complex, such as turning one's head and shrugging one's shoulders or rehashing an action.6,7
Tics decrease significantly during sleep and increase dramatically in stressful, exciting, and tiring situations. Unfortunately, symptoms of TS and other tic disorders can be socially inappropriate, and as a result, many people are victimized and isolated from social environments.8 The diminished self-esteem and accompanying psychiatric issues can expose individuals to additional potential problems.8,9 Studies suggest that certain psychiatric disorders, such as mood disorders and self-injurious behavior, share a genetic basis with TS.10 The symptoms of anxiety and depression accompanying TS pose a greater threat to patients’ social and functional performance than tics themselves.11 In patients with autism,12 attention-deficit/hyperactivity disorder,13 obsessive-compulsive disorder,14 and Down syndrome,15 the prevalence of TS has increased. In terms of its etiology, genetic, neurochemical, neuroanatomic, immunologic, and consequently infectious factors (among others) have been discussed.16, 17, 18
Several early studies on the prevalence of TS worldwide were conducted in small environments with smaller sample sizes. Scharf et al. and Levine et al. conducted the most recent meta-analyses regarding the prevalence of TS.19,20 Scharf et al. conducted their study in 2015 but did not include studies conducted before that year. In addition, this study did not examine the studies conducted from 2015 to 2022. In contrast, the study by Levine et al. focused solely on the prevalence of TS in adults and analyzed only three articles.
Furthermore, none of the studies examined the effects of potential variables such as the year, sample size, qualitative assessment score, diagnostic instruments, and gender. In addition, the studies failed to report the prevalence rate by population subgroup (i.e., specific information for each continent and age group). Moreover, there are contradictions between their findings. Consequently, the purpose of the present study was to determine the global prevalence of TS using a systematic review/meta-analysis approach.
Section snippets
Methods
The current systematic review/meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) 2020 identification, screening, eligibility, and inclusion criteria.21 To reduce the effects of publication bias and errors, researchers independently performed the phases of searching, evaluating, selecting articles, and collecting data (F.J. and M.K.). Moreover, conflicts were resolved initially through discussion and subsequently through the
A summary of the articles included in the meta-analysis
The preliminary search yielded 2688 studies employing strategies for identifying studies from various databanks. However, 1456 duplicate and overlapping studies from various databanks were eliminated. After reviewing the titles and abstracts of the remaining 1232 studies, 1182 records were determined to be irrelevant to the research topic and were therefore eliminated. Then, the full texts of the remaining 50 studies were examined, and 20 records that did not meet the inclusion criteria were
Discussion
The purpose of the present systematic review and meta-analysis was to determine the global prevalence of TS. Combining the results of 30 studies (39 results) led to the conclusion that the global prevalence of TS is 0.5%. The highest prevalence was found in a Canadian study of patients with various nervous disorders, with 17%,52 whereas the lowest prevalence was found in a study of adults aged 50 years and older, with 0.003%.49 According to the JBI checklist, the study with the highest quality
Conclusion
This comprehensive review and meta-analysis revealed that the prevalence of TS worldwide can be deemed nearly high. Therefore, it seems necessary to draw the attention of health field specialists, officials, and policymakers.
Acknowledgments
The Student Research Committee of Kermanshah University of Medical Sciences approved this study as research project number 50000942. We would like to thank the esteemed officials of that institution for agreeing to cover the costs of this study.
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Cited by (0)
Author's contributions: M.K. and F.J. contributed to the design, and M.K. and P.A. participated in most of the study steps. M.K., M.R., and F.J. prepared the manuscript. F.J., P.A., and M.K. assisted in designing the study and helped in the interpretation of the study. All authors have read and approved the content of the manuscript.
Funding: Funding was provided by the Department of Research and Technology, Kermanshah University of Medical Sciences (IR) (50000942). This department had no impact on the study's development.
Availability of data and materials: Datasets are available through the corresponding author upon reasonable request.
Ethics approval and consent to participate: Ethics approval was granted by the Ethics Committee of the Department of Research and Technology at Kermanshah University of Medical Sciences (IR.KUMS.REC.1400.780).
Consent for publication: Not applicable.
Competing interests: The authors declare that they have no conflict of interest.