Yale Global Tic Severity Scale (YGTSS): Psychometric Quality of the Gold Standard for Tic Assessment Based on the Large-Scale EMTICS Study

The Yale Global Tic Severity Scale (YGTSS) is a clinician-rated instrument considered as the gold standard for assessing tics in patients with Tourette's Syndrome and other tic disorders. Previous psychometric investigations of the YGTSS exhibit different limitations such as small sample sizes and insufficient methods. To overcome these shortcomings, we used a subsample of the large-scale “European Multicentre Tics in Children Study” (EMTICS) including 706 children and adolescents with a chronic tic disorder and investigated convergent, discriminant and factorial validity, as well as internal consistency of the YGTSS. Our results confirm acceptable convergent and good to very good discriminant validity, respectively, indicated by a sufficiently high correlation of the YGTSS total tic score with the Clinical Global Impression Scale for tics (rs = 0.65) and only low to medium correlations with clinical severity ratings of attention deficit/hyperactivity symptoms (rs = 0.24), obsessive–compulsive symptoms (rs = 27) as well as internalizing symptoms (rs = 0.27). Internal consistency was found to be acceptable (Ω = 0.58 for YGTSS total tic score). A confirmatory factor analysis supports the concept of the two factors “motor tics” and “phonic tics,” but still demonstrated just a marginal model fit (root mean square error of approximation = 0.09 [0.08; 0.10], comparative fit index = 0.90, and Tucker Lewis index = 0.87). A subsequent analysis of local misspecifications revealed correlated measurement errors, suggesting opportunities for improvement regarding the item wording. In conclusion, our results indicate acceptable psychometric quality of the YGTSS. However, taking the wide use and importance of the YGTSS into account, our results suggest the need for further investigations and improvements of the YGTSS. In addition, our results show limitations of the global severity score as a sum score indicating that the separate use of the total tic score and the impairment rating is more beneficial

Lack of Association of Group A Streptococcal Infections and Onset of Tics: European Multicenter Tics in Children Study

Background and objectives: The goal of this work was to investigate the association between group A streptococcal (GAS) infections and tic incidence among unaffected children with a family history of chronic tic disorders (CTDs). Methods: In a prospective cohort study, children with no history for tics who were 3 to 10 years of age with a first-degree relative with a CTD were recruited from the European Multicentre Tics in Children Study (EMTICS) across 16 European centers. Presence of GAS infection was assessed with throat swabs, serum anti-streptolysin O titers, and anti-DNAse titers blinded to clinical status. GAS exposure was defined with 4 different definitions based on these parameters. Cox regression analyses with time-varying GAS exposure were conducted to examine the association of onset of tics and GAS exposure during follow-up. Sensitivity analyses were conducted with Cox regression and logistic regression analyses. Results: A total of 259 children were recruited; 1 child was found to have tic onset before study entry and therefore was excluded. Sixty-one children (23.6%) developed tics over an average follow-up period of 1 (SD 0.7) year. There was a strong association of sex and onset of tics, with girls having an ≈60% lower risk of developing tics compared to boys (hazard ratio [HR] 0.4, 95% confidence interval [CI] 0.2-0.7). However, there was no statistical evidence to suggest an association of any of the 4 GAS exposure definitions with tic onset (GAS exposure definition 1: HR 0.310, 95% CI 0.037-2.590; definition 2: HR 0.561, 95% CI 0.219-1.436; definition 3: HR 0.853, 95% CI 0.466-1.561; definition 4: HR 0.725, 95% CI 0.384-1.370). Discussion: These results do not suggest an association between GAS exposure and development of tics. Classification of evidence: This study provides Class I evidence that group A streptococcal exposure does not associate with the development of tics in children with first-degree relatives with chronic tic disorder

Vitamin D levels in children and adolescents with chronic tic disorders: a multicentre study

This study investigated whether vitamin D is associated with the presence or severity of chronic tic disorders and their psychiatric comorbidities. This cross-sectional study compared serum 25-hydroxyvitamin D [25(OH)D] (ng/ml) levels among three groups: children and adolescents (3-16 years) with CTD (n = 327); first-degree relatives (3-10 years) of individuals with CTD who were assessed for a period of up to 7 years for possible onset of tics and developed tics within this period (n = 31); and first-degree relatives who did not develop tics and were ≥ 10 years old at their last assessment (n = 93). The relationship between 25(OH)D and the presence and severity of tics, as well as comorbid obsessive-compulsive disorder (OCD) and attention-deficit/hyperactivity disorder (ADHD), were analysed controlling for age, sex, season, centre, latitude, family relatedness, and comorbidities. When comparing the CTD cohort to the unaffected cohort, the observed result was contrary to the one expected: a 10 ng/ml increase in 25(OH)D was associated with higher odds of having CTD (OR 2.08, 95% CI 1.27-3.42, p < 0.01). There was no association between 25(OH)D and tic severity. However, a 10 ng/ml increase in 25(OH)D was associated with lower odds of having comorbid ADHD within the CTD cohort (OR 0.55, 95% CI 0.36-0.84, p = 0.01) and was inversely associated with ADHD symptom severity (β = - 2.52, 95% CI - 4.16-0.88, p < 0.01). In conclusion, lower vitamin D levels were not associated with a higher presence or severity of tics but were associated with the presence and severity of comorbid ADHD in children and adolescents with CTD