Study design and participants

The design of this controlled study was previously described in details elsewhere [15]. Over a period of 3 years in France, before the COVID-19 pandemic, adolescents aged 12–18 years diagnosed with TS according to DSM-IV-TR criteria were recruited with their parents (TS family) from primary and secondary referral centres during a consultation. Exclusion criteria for adolescents and parents were intellectual disability according to DSM-IV-TR criteria and inability to understand or complete the questionnaires.

During this consultation, a neurologist assessed the severity of the tics of TS adolescents using the Yale Global Tic Severity Scale (YGTSS) [16] and a psychiatrist assessed their obsessive–compulsive symptoms using the Children’s Yale-Brown Obsessive–Compulsive Scale (CY-BOCS) [17].

Adolescent healthy controls without TS matched for gender and age and their parents were also recruited. The control family was chosen by the TS family to take part in the study. They had to live in the same region, be composed of the same number of children and have no family relationship with the TS family.

A set of questionnaires was mailed with a return envelope to all the adolescents and each of their parents (mothers and fathers) 2 weeks after the consultation during which they were recruited for the TS group, and 2 weeks after giving their informed consent to participate for the control family. The adolescents, mothers and fathers were instructed to self-complete the questionnaires independently.

The study was approved by the French Committee for the Protection of Individuals southeast 6 (reference CPP AU803, 30 November 2009) and was conducted in accordance with the Declaration of Helsinki. All parents gave their written informed consent. Consent for minor adolescents was obtained from their parents prior to participation.

MeasuresHRQoL of adolescents

The HRQoL of adolescents during the previous 4 weeks was assessed by the ‘Vécu et Santé Perçue de l’Adolescent’ questionnaire [18], which comprises 37 items grouped into ten subscales: ‘Vitality’ (5 items), ‘Psychological well-being’ (5 items), ‘Relationship with friends’ (5 items), ‘Leisure activities’ (4 items), ‘Relationship with parents’ (4 items), ‘Physical well-being’ (4 items), ‘Relationship with teachers’ (3 items), ‘School performance’ (2 items), ‘Body image’ (2 items) and ‘Relationship with medical staff’(3 items) (not studied here). Each item is rated on a 5-point Likert scale from 1 (“not at all/never”) to 5 (“very much/always”). For each subscale, a total score is calculated as the mean of the item scores of the subscale. The scoring of item response is reversed when necessary so that higher scores indicates better HRQoL. A missing score is assigned if more than one-half of the items in each subscale are missing. All scores are linearly transformed on a scale from 0 (indicating the worst HRQoL) to 100 (the highest HRQoL). Two parallel self-administered questionnaires are available with identical items: an adolescents’ self-administered version (VSP-A) and a parents’ one to assess the HRQoL of their children (VSP-P) [19]. The items of the parents’ form were reworded following this example “Was your child anxious?” instead of “Were you anxious?”.

Tics and obsessive–compulsive symptoms of TS adolescents

The Motor tic, Obsessions and compulsions, Vocal tic Evaluation Survey (MOVES) was self-completed by adolescents to assess severity of their tics and related sensory phenomena observed in TS [20]. It comprises 20 items measuring the past 4 weeks’ severity of five phenomena: ‘Motor tics’, ‘Vocal tics’, ‘Obsessions’, ‘Compulsions’ and ‘Associated symptoms’ (echolalia, echopraxia, coprolalia, copropraxia). For each subscale, a score is obtained by adding the scores of the items listed in the subscale. A total MOVES score is calculated by adding the scores of these five subscales, with range from 0 (no symptom) to 60 (the worst condition). The ‘Motor tics’ and ‘Vocal tics’ scores are added to form a ‘Tic’ subscale score. The ‘Obsessions’ and ‘Compulsions’ scores are added to form an ‘Obsessions- Compulsions’ subscale score.

Behavioural and emotional problems of adolescents

The Child Behaviour Checklist (CBCL) for ages 6–18 years was self-completed by both mothers and fathers to assess the presence of adolescents’ behavioural and emotional problems [21]. It is a useful screening-diagnostic tool to identify the main psychiatric and behavioural problems in TS [22]. The CBCL provides scores for three broad-band subscales: ‘Internalizing symptoms’, ‘Externalizing symptoms’ and ‘Total problems’. Higher scores for each subscale denotes greater problems. Raw scores were transformed into T-scores to obtain for adolescents the nonclinical, borderline clinical and clinical profiles according to standardization and cut-offs [23].

HRQoL of parents

Parents’ HRQoL was assessed by two self-administered questionnaires, the Medical Outcomes Study Item Short Form Health Survey (SF-36) [24] and the World Health Organization Quality of Life Brief (WHOQOL-BREF) [25] questionnaire. The SF-36 consists of 36 items assigned to eight multi-item subscales: ‘Physical functioning’, ‘Role physical’; ‘Bodily pain’, ‘Vitality’, ‘Mental health’, ‘Role emotional’, ‘Social functioning’ and ‘General health’. The WHOQOL-BREF comprises four subscales: ‘Physical health’, ‘Psychological health’, ‘Social relationships’ and ‘Environment’. For each subscale of the SF-36 and WHOQOL-BREF, scores between 0 and 100 are established, with higher values indicating better HRQoL.

Psychiatric morbidity of parents

Anxiety and depressive symptoms of parents were assessed by the Hospital Anxiety and Depression Scale (HADS) [26], a self-report scale consisting of 14 items, 7 related to anxiety (HADS-A) and 7 to depression (HADS-D). For both depression and anxiety, a total score ranging from 0 to 21 is calculated, with higher scores representing a higher level of symptoms of depression and anxiety. The HADS scores can also be interpreted by cut-off scores, with a score strictly higher than 7 indicating a possible or probable clinical case [27].

Demographic and clinical information

Sex of adolescents, age, and clinical data on TS were collected: time since first symptoms, time since diagnosis, medical treatment, follow-up care and current health problems. For each of the parents, age, marital status, level of education, family size, current health problems, medical treatment and family medical history in connection with TS were collected.

Statistical analysis

All analyses were performed with SAS software (version 9.4, SAS Institute, Cary, NC, 2002–2012) and conducted at a two-sided alpha = 0.05 significance level. Because of the explorative nature of our study, no adjustment for multiple testing was done (this would have overestimated the role of chance) [28, 29].

Continuous variables were presented as means and standard deviations and categorical variables as numbers and percentages.

Mother-adolescent, father-adolescent and mother-father agreements on adolescents’ HRQoL scores were investigated at the individual and group level, both in the TS and control groups.

At the individual level, the intraclass correlation coefficients (ICCs) using two-way mixed effects models with absolute agreement definition were calculated per dyad. Values of ICC inferior to 0.19 were interpreted as poor agreement, between 0.20 and 0.39 as fair agreement, between 0.40 and 0.59 as moderate agreement, between 0.60 and 0.79 as good agreement, and values equal or superior to 0.80 as excellent agreement [30]. The ICCs were compared based on their 95% confidence intervals.

At the group level, different approaches were used to assess agreement in the TS group. First, mean absolute difference between scores (proxy minus adolescent scores, mother minus father scores, irrespective of the direction of the discrepancies) and mean directional difference (showing the direction of the discrepancies) were calculated. A negative mean difference shows lower parent-proxy report of HRQoL compared to adolescent self-reported scores or lower mother-proxy report compared to father proxy-report. Second, Student paired t tests were used to assess differences between HRQoL scores in mother-adolescent, father-adolescents and mother-father dyads. Third, effect sizes (ES) were used to evaluate the magnitude of the directional differences for paired observations, and were defined as the ratio of the mean difference to its SD. A negative ES indicated a lower level of adolescents’ HRQoL reported by parents compared to adolescents or reported by mothers compared to fathers. Effect sizes can be interpreted as: negligible for |< 0.20|, small for |0.20–0.49|, moderate for |0.50–0.79|, and large for |≥ 0.80| [31].

Directional differences in each dyad were compared between TS and control groups using unpaired Student t tests.

The HRQoL subscales for which parents of TS adolescents had significantly differences in discrepancies between mother-adolescent, father-adolescent and mother-father dyads in comparison to control parents were included in the analysis of demographic and clinical factors affecting concordance in dyads. Multivariate linear regression models with a forward selection were used to test the effect of individual variables on dyads agreement for each HRQoL subscale separately. We included in the model independent variables significant in the bivariate analyses at p < 0.15. Directional differences were the dependent variables. Independent variables were adolescents’ factors (gender, age, time since first symptoms and diagnosis, treatment reported for tics, VSP-A, YGTSS, CY-BOCS, MOVES, and CBCL scores) and parental factors (age, level of education, family size, health problems, SF-36, WHOQOL-BREF and HADS scores).