The purpose of this trial is to evaluate the clinical efficacy, 12-month durability, and cost-effectiveness of BIP TIC - a therapist-guided and parent-guided internet-delivered behavioural intervention for children and adolescents with Tourette's Disorder and Persistent (Chronic) Motor or Vocal Tic Disorder.

Primary objective: To determine the clinical efficacy of BIP TIC (Andrén et al., 2019; a therapist-guided and parent-guided, internet-delivered behavioural intervention for Tourette's Disorder (TD) and Persistent (Chronic) Motor or Vocal Tic Disorder (PTD), for reducing tic severity (as measured by the primary outcome variable Yale Global Tic Severity Scale [YGTSS] Total Tic Severity Score [TTSS]) in children and adolescents with TD/PTD, compared with a control intervention (therapist-guided and parent-guided internet-delivered education on tics).

Secondary objectives: To establish the 12-month durability of the treatment effects, and to assess the cost-effectiveness of BIP TIC, compared with therapist-guided and parent-guided internet-delivered education on tics, from a societal perspective.

Type of trial: Single-blind parallel-group randomised controlled superiority trial.

Trial design and methods: All potential participants are initially screened via the telephone, or in some cases at the clinic. This is followed by an inclusion assessment conducted either at the clinic or via the videoconference software Zoom. Participants who are eligible and have consented will be randomised into one of two trial arms. In the experimental arm, participants receive 10 weeks of therapist-guided and parent-guided internet-delivered exposure and response prevention (ERP). In the control arm, participants receive 10 weeks of therapist-guided and parent-guided internet-delivered education on tics. Participants will complete outcome measures at baseline, mid-treatment (3 and 5 weeks post-baseline), post-treatment (10-weeks post-baseline) and 3, 6 and 12 months post-treatment. To allow for holidays or periods of sick leave, it is possible to extend the duration of the treatment from 10 to a maximum of 12 weeks (of which only 10 weeks will include therapist support). In these cases, the listed time frames in the "Outcome Measures" section will be extended with the equivalent number of weeks.

The primary outcome variable is the Total Tic Severity Score (TTSS) of the Yale Global Tic Severity Scale (YGTSS), and the primary endpoint is the follow-up 3-months post-treatment. For secondary outcomes, see section below. Follow-up assessments will be conducted at the clinic or via Zoom videoconference software, in both cases complemented with online questionnaires.

Planned trial sites: All assessments and delivery of treatment will be administrated from a single site in Stockholm, the Child and Adolescent Psychiatry Research Center. Several collaborating counties all across Sweden will assist on referring potential participants to the Stockholm site for inclusion in the trial.

Sample: 220 participants.

Statistical methodology and analysis: Data will be analysed using a pre-specified intention-to-treat statistical analysis plan.

Inclusion Criteria:

1. Aged 9 to 17 years. Confirmed by the caregiver and subsequently by the patient record system TakeCare.
2. A diagnosis of Tourette's Disorder or Persistent (Chronic) Motor or Vocal Tic Disorder, based on the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Confirmed by the assessor at the face-to-face or videoconference inclusion assessment.
3. A Total Tic Severity Score (TTSS) of >15 (or >10 if only motor or vocal tics, but not both, have been present the last week) on the YGTSS. Confirmed by the assessor at the face-to-face or videoconference inclusion assessment.
4. A minimum of one available caregiver (parent) to support the child/adolescent throughout the treatment. Confirmed by the caregiver at the telephone screening or/and face-to-face or videoconference inclusion assessment.
5. Regular access to a desktop or laptop computer connected to the internet, with the ability to receive e-mails, as well as a mobile phone to receive SMS (one of each is enough per family). Confirmed by the caregiver at the telephone screening or/and face-to-face or videoconference inclusion assessment.

Exclusion Criteria:

1. Previous behaviour therapy for tics, for a minimum of eight sessions with a qualified therapist within the 12 months prior to assessment. Confirmed by the caregiver at the telephone screening or/and face-to-face or videoconference inclusion assessment.
2. Simultaneous psychological treatment for Tourette's Disorder or Persistent (Chronic) Motor or Vocal Tic Disorder. Confirmed by the caregiver at the telephone screening or/and face-to-face or videoconference inclusion assessment.
3. Initiation or adjustment of any psychotropic medication for Tourette's Disorder or Persistent (Chronic) Motor or Vocal Tic Disorder within the eight weeks prior to assessment. Confirmed by the caregiver at the telephone screening or/and face-to-face or videoconference inclusion assessment.
4. A diagnosis of organic brain disorder, intellectual disability, autism spectrum disorder, psychosis, bipolar disorder, anorexia nervosa, or alcohol/substance dependence. Confirmed by the assessor at the telephone screening or/and face-to-face or videoconference inclusion assessment, with help of information from the caregiver and the child/adolescent, and the Mini International Neuropsychiatric Interview for Children and Adolescents (MINI-KID) interview.
5. Immediate risk to self or others, requiring urgent medical attention, such as suicidality, or self-injurious tics. Confirmed by the assessor at the telephone screening or/and face-to-face or videoconference inclusion assessment.
6. Child or caregiver (parent) not able to read and communicate in Swedish. Confirmed by the caregiver or assessor at the telephone screening or/and face-to-face or videoconference inclusion assessment.
7. A participant with a close relationship to the child/adolescent (e.g., sibling, cousin) has already been included in the trial.

Assessors conducting post- and follow-up assessments will be blind to treatment allocation, for the full duration of the trial. At each follow-up assessment, participants will be reminded by their assessor to not reveal their arm allocation. To measure blinding integrity, all assessors will record whether the participating families inadvertently reveal their group allocation, and subsequently guess each participant's treatment allocation at each assessment point, and motivate their choice. If the treatment allocation is accidently revealed, that very part will be cut out of the video recording, and a new blind assessor will watch the video and conduct the assessment that will be used in the trial. Subsequent assessments for that participant will then be conducted by a different assessor (than the first one; blind to treatment allocation), where possible. The blinding will be broken after the trial's final participant has finished her/his 3-month follow-up assessment (primary endpoint).