F1000Research F1000Research 2046-1402 F1000 Research Limited London, UK 10.12688/f1000research.169442.1 Study Protocol Articles Study Protocol: Single-Arm Pilot Feasibility of a Short-Term Family-Based Mentalization Approach for Early Adolescents with Depression

[version 1; peer review: awaiting peer review]

 Morán-Kneer Javier Conceptualization Data Curation Funding Acquisition Investigation Methodology Project Administration Resources Writing – Original Draft Preparation Writing – Review & Editing https://orcid.org/0000-0002-2633-3167 a 1 Duarte Javiera Funding Acquisition Investigation Methodology Project Administration Writing – Original Draft Preparation https://orcid.org/0000-0002-7569-0048 2 Zapata Johana Methodology Supervision Writing – Original Draft Preparation 3 Alkabes-Esquenazi Louise Investigation Methodology Writing – Original Draft Preparation Writing – Review & Editing 4 González Silvia Investigation Supervision Writing – Original Draft Preparation Writing – Review & Editing 1 Solervicens Paula Methodology Writing – Original Draft Preparation Writing – Review & Editing 1 Klagges Melanie Conceptualization Methodology Writing – Original Draft Preparation Writing – Review & Editing https://orcid.org/0000-0002-7422-773X 5 Díaz Francisca Investigation Methodology Writing – Original Draft Preparation Writing – Review & Editing 1 Arancibia Marcelo Investigation Methodology Supervision Writing – Original Draft Preparation Writing – Review & Editing 1 García Francisca Methodology Writing – Original Draft Preparation 1 Ávalos Nicole Conceptualization Project Administration Writing – Original Draft Preparation Writing – Review & Editing 1 Universidad de Valparaiso, Valparaíso, Chile Universidad Diego Portales, Santiago, Chile Universidad Autonoma de Chile, Santiago, Santiago, Chile Universidad Catolica Santa Maria La Antigua, Panama City, Panama Hospital Clinico San Borja Arriaran, Santiago, Chile javier.moran@uv.cl

No competing interests were disclosed.

 8 12 2025 2025 14 1373 21 11 2025 Copyright: © 2025 Morán-Kneer J et al. 2025 This is an open access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background

Adolescent depression affects approximately 13% of youth globally, often emerging before age 14 and leading to long-term impairments in social, academic, and emotional functioning. Evidence suggests that mentalization-based treatment (MBT), particularly its adolescent adaptation, may reduce depressive symptoms by strengthening reflective functioning.

 Methods

This single-arm pilot study will evaluate the feasibility and acceptability of a short-term, family-inclusive MBT intervention for 15 adolescents aged 10–14 years with mild-to-moderate depression in Valparaíso, Chile. The intervention consists of 12 weekly sessions delivered in three phases: shared formulation, promotion of individual and family mentalization, and evaluation of therapeutic progress. Feasibility outcomes include recruitment, retention, and adherence rates. Secondary outcomes include changes in depressive and anxiety symptoms, family cohesion, and therapeutic processes. Qualitative interviews with adolescents, caregivers, and therapists will complement quantitative data.

 Results

The study will generate parameters on feasibility, adherence, and acceptability, as well as preliminary estimates of clinical and process outcomes to inform the design of a future randomized controlled trial.

 Conclusions

Findings will guide the cultural adaptation and potential scaling of adolescent and family MBT within the Chilean public health system. This protocol outlines the methodological framework and expected contributions of the study to clinical practice and research on adolescent depression.

 Adolescent depression Mentalization-Based Treatment feasibility study family intervention short-term psychotherapy emotional pilot study. Agencia Nacional de Investigación y Desarrollo FONISSA22I0168 This project was supported by the National Fund for Health Research (FONIS), Chile, through project SA22I0168. The funding body had no role in the design of the study; collection, management, analysis, or interpretation of data; writing of the report; or the decision to submit the manuscript for publication. All responsibility for these activities rests with the research team. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Introduction

Depression affects about 13.4% of children and adolescents worldwide, 1 with most mental health problems emerging before age 14. 2 These conditions disproportionately affect vulnerable groups, 3 impose long-term costs on health systems, 4 and in adolescence are strongly linked to self-harm and suicidal behavior. 5 Adolescent depression also frequently co-occurs with substance use, risky sexual behaviors, anxiety, and personality disorders. 6, 7 Early-onset depression is particularly concerning, as it is associated with neurodevelopmental impairments 8 and persistent impacts on academic, social, and emotional functioning, 9– 11 often leading to recurrent episodes. 12 The COVID-19 pandemic further intensified the problem, contributing to a 25% global increase in depression and anxiety 13 and producing major consequences for education, rights, poverty, and overall well-being. 14– 16

Moreover, early adolescence serves as a critical period for brain development due to synaptic pruning, a crucial process for the maturation of regions involved in executive functions, emotional regulation, and social behavior. 17 Disruptions in synaptic pruning can lead to maladaptive neural circuitry, which impacts emotional regulation and heightens the risk of depression. 18 According to this evidence, addressing depression early in adolescence is crucial to mitigate these risks and support healthier developmental trajectories. 19

Importantly, these neural changes also impact adolescents’ capacity for mentalization—the ability to understand the mental states of oneself and others. 20 Research has shown that the development and reorganization of brain areas during adolescence, particularly those involved in social cognition and executive functions, are crucial for the enhancement of mentalizing abilities. 21, 22 Recent studies have indicated that mental health disorders, including depression, are linked to dysfunctions in mentalizing capacities. 23 Failures in mentalizing may play a crucial role in the development of depressive symptoms. 24 During this time, adolescents must also develop new capabilities such as establishing relationships, gaining greater autonomy, and enhancing agency. These developments largely depend on the regulation of stress, mentalization, and reward systems. Consequently, poor mentalizing is linked to higher rates of depression during developmental transitions. 25

Building on this evidence, mentalization-based treatment (MBT), and its adolescent adaptation (MBT-A), has shown efficacy in reducing depressive symptoms. A randomized trial 26 found that a 12-session MBT-A program outperformed treatment as usual (TAU) in reducing depression and self-harm, while a pilot group-based adaptation 27 demonstrated feasibility and similar reductions in self-harm. More recently, MBT has expanded to family and community formats, 28, 29 reflecting evidence that adolescents’ symptoms are closely tied to parental well-being and family functioning. 30– 32 Conversely, poor communication, parental psychopathology, and family dysfunction increase risks. 33– 36 Parental involvement strengthens treatment effects by promoting emotional coregulation 37 and by supporting regulation strategies that reduce behaviors interfering with therapy. 38

In summary, we propose that mentalization-based psychotherapy, integrating both individual and family components, may represent a promising approach for early adolescent depression. This protocol outlines a single-arm feasibility pilot in Chile, designed to evaluate recruitment, retention, adherence, and acceptability, providing essential parameters to inform the development of a future randomized controlled trial.

 Protocol Study design

This is a single-arm, mixed-methods feasibility pilot study of a short-term, family-inclusive mentalization-based therapy (MBT-A) for adolescents with mild to moderate depression attending a primary care center in Valparaíso, Chile. The study integrates quantitative and qualitative approaches to evaluate feasibility, acceptability, and preliminary clinical outcomes. The design follows the Consolidated Standards of Reporting Trials (CONSORT) extension for randomized pilot and feasibility trials 39 and the SPIRIT guidelines for protocol reporting. 41 According to CONSORT, such designs are recommended to evaluate feasibility on a small exploratory scale before scaling up to randomized controlled trials (RCTs), and they allow documentation of design modifications such as treatment type, eligibility criteria, and outcome variables. 40 The Trial registration can be found on ichgcp.net NCT06252090.

 Aims

This feasibility pilot study aims to assess the feasibility and acceptability of a short-term mentalization-based treatment for adolescents diagnosed with mild to moderate depression.

The primary objectives are:

To estimate the recruitment rate (proportion of invited patients who agree to participate).

To estimate the adherence rate (proportion of patients completing the intervention relative to the initial sample).

To explore the intervention’s effect size on adolescent depressive symptoms.

To examine patient satisfaction (acceptability) and the applicability of the treatment from the perspectives of therapists and supervisors.

The secondary objectives are:

To estimate the intervention’s effect size on depressive symptoms in other family members.

To assess the effect size on anxiety symptoms in all participants.

To evaluate changes in family cohesion.

To explore overall adaptation of family system members.

Participants and setting Setting

The study is being conducted at a teaching-assisted psychological care clinic linked to secondary mental health services in Valparaíso, Chile. In the Chilean public health system, adolescents with suspected depression are typically referred from primary care to specialized secondary centers. This protocol is embedded within that referral pathway.

 Participants

Fifteen adolescents aged 10 to 14 years, diagnosed with mild to moderate major depressive disorder according to DSM-5-TR criteria. 57 Diagnosis will be established through a structured clinical interview conducted online by a child and adolescent psychiatrist. Each assessment will last approximately one hour and will include separate interviews with the primary caregiver and the adolescent to explore symptoms, functional impairment, and contextual factors relevant to diagnosis. Healthcare providers at these centers will conduct the initial screening and refer eligible patients until the target sample is reached. Caregivers of adolescents identified as potentially eligible will be contacted by the research team and invited to participate. Written informed consent will be obtained from caregivers, and assent from adolescents. No financial compensation will be provided. Interventions will take place at a teaching-assisted psychological care clinic in Valparaíso.

 Eligibility criteria

Inclusion requires at least one legally responsible adult willing to participate in the therapeutic process. Exclusion criteria include autism spectrum disorder, psychosis, bipolar disorder, active suicidal ideation, substance use disorder, and pregnancy. These criteria were defined to ensure participant safety and the appropriateness of the intervention. All participants must be users of the public healthcare system.

 Recruitment

Healthcare providers from primary centers conduct initial screening and refer potentially eligible patients. The research team contacts caregivers of referred adolescents to provide study information and invite participation. Written informed consent is obtained from caregivers and assent from adolescents. Reasons for refusal or withdrawal will be documented where available. No financial compensation is provided.

Recruitment will be conducted through close collaboration with primary healthcare providers, who will actively identify eligible adolescents during routine consultations and refer them directly to the study. The research team will maintain regular communication with referral centers to ensure timely follow-up of potential participants. Flexibility in scheduling assessments and sessions will be offered to accommodate families’ availability, and reminder calls will be used to minimize missed appointments. Reasons for refusal or withdrawal will be systematically recorded to inform strategies for improving enrolment in future trials.

 Timeline and registration

Recruitment began on September 1, 2023, and is expected to conclude on July 1, 2025. Participant follow-up will continue until September 2025. The study is registered at ClinicalTrials.gov (NCT06252090).

 Intervention

Description of the intervention

The intervention is a short-term adaptation of mentalization-based therapy for adolescents (MBT-A), designed to enhance adolescents’ capacity for mentalization and thereby reduce depressive symptoms. The program integrates both individual and family sessions and maintains the core features of MBT, including the therapist’s active stance in promoting mentalization, recognition of the uncertainty of mental states, focus on the here and now, and the use of affect as a mechanism for change.

The treatment is structured into 12 weekly sessions, delivered in three phases with flexible content tailored to each family’s needs.

Phase 1 (sessions 1–3): Development of a shared understanding of the presenting problems, culminating in a written clinical formulation shared with the family.

Phase 2 (sessions 4–9): Intensive promotion of mentalization at both individual and family levels, based on the therapeutic focus established in Phase 1.

Phase 3 (sessions 10–12): Evaluation of progress and planning of strategies to maintain therapeutic gains.

The intervention incorporates a psychoeducational component, presented via a short animated video in Phase 1, which explains depression from a mentalization perspective, its manifestations in adolescence, and the role of the family in treatment. Routine outcome monitoring is used to track symptoms throughout the intervention.

 Therapists and training

The intervention will be delivered by clinical psychologists and child and adolescent psychiatrists, all with at least five years of clinical experience with families and/or adolescents. Therapists will receive three days of basic MBT-A training from a certified instructor. To ensure treatment fidelity, all sessions will be video-recorded and independently assessed using the Mentalization-Based Treatment Adherence and Competence Scale (MBT-ACS). 53 Two pairs of clinical psychologists, all experienced in adolescent and family therapy and trained by an MBT expert in adherence evaluation, will conduct the ratings. Discrepancies between raters will be resolved through consensus discussions, with the support of an expert in the MBT model and clinical competence assessment. Inter-rater reliability will be calculated using intraclass correlation coefficients (ICC) to ensure scoring consistency. Group supervision sessions will be held regularly to support adherence to the model and reflect on clinical development. Additionally, eight structured supervision sessions with an MBT-A expert supervisor will be conducted throughout the study. Independent judges’ evaluations of adherence will be integrated into weekly supervision.

 Outcomes

Primary outcomes

The primary outcomes relate to feasibility and acceptability of the intervention.

Feasibility will be assessed by:

Recruitment rate (proportion of eligible adolescents who agree to participate).

Attrition rate (number of participants withdrawing before completion).

Follow-up rate at post-treatment and follow-up assessments.

Qualitative reports from therapists and supervisors obtained through structured interviews.

Acceptability will be evaluated by:

Adherence rate (proportion of participants completing the 12 sessions).

Reports from adolescents and caregivers through qualitative interviews.

Responses to the Credibility/Expectancy Questionnaire (CEQ). 42

Secondary outcomes

Secondary outcomes focus on clinical and family-level changes associated with the intervention.

For caregivers:

Depressive symptoms assessed with the PHQ-9. 43, 44

Anxiety symptoms assessed with the DASS-21 anxiety scale. 45, 46

For adolescents:

Depressive symptoms assessed with the Revised Child Anxiety and Depression Scale (RCADS-30). 47– 49

Externalizing and internalizing symptoms assessed with the Strengths and Difficulties Questionnaire, short form (SDQ-SF). 50

For the family system:

Family cohesion assessed using FACES III. 51

Details regarding the application procedures and data safeguarding are outlined in the ethics protocol approved by Institutional Ethics Committee of the University of Valparaíso (CEC-UV 262-22).

An overview of all primary and secondary outcome measures, together with their timing across study phases, is presented in Table 1.

Overview of the assessments according to time points.
SCREENING T0 T1 T2 T3
ENROLMENT
Eligibility screen X
Informed consent X
Psychiatrist assessment X
INTERVENTION
MBT intervention X
ASSESMENTS
Adult PHQ-9 X X X
SDQ X X X
FACES III X X X
CEQ X X
DASS-21 X X X
CORE-OM X
Adolescent RCADS-30 X X X
YP-CORE-OM X X X
CEQ X
Observation Instruments OMP-A X
MBT-ACS X
VTAS-SF X

T0: Baseline, T1: Intervention, T2: Postintervention, T3: Follow-up, PHQ-9: Patient Health Questionnaire, SDQ: Strengths and Difficulties Questionnaire, FACES III: Family Adaptability and Cohesion Evaluation Scale, CEQ: Credibility/Expectancy Questionnaire DASS-21: Depression Anxiety Stress Scales, CORE-OM: Clinical Outcomes in Routine Evaluation – Outcome Measure, RCADS-30: Revised Child Anxiety and Depression Scale, YP-CORE-OM: Young Person-Clinical Outcomes in Routine Evaluation-Outcome Measure, OMP-A: Observing the Mentalization in Psychotherapy for Adolescents Scale, MBT-ACS: Mentalization-based Therapy Adherence and Competence Scale, VTAS-SF: Vanderbilt Therapeutic Alliance Scale.

 Additional process outcomes

Additional outcomes will capture therapeutic processes and change mechanisms.

Therapy process assessments by external observers:

Therapeutic alliance (VTAS-SF). 52

Adherence to the MBT model (MBT-ACS). 53

Observed mentalization in adolescents (OMP-A). 54

Routine outcome monitoring:

Psychological well-being of caregivers will be measured session by session with the CORE-OM. 55

Psychological well-being of adolescents will be measured session by session with the YP-CORE-OM. 56

Sample size and feasibility thresholds

The target sample size is 15 adolescents and their families. This number was chosen pragmatically to reflect the exploratory nature of a feasibility pilot while providing sufficient data to examine recruitment, retention, and adherence rates, as well as preliminary effect size estimates.

Sample size calculation was guided by previous evidence from Rossouw and Fonagy, 26 which reported substantial clinical improvements in similar populations. Based on these findings, a large effect size for depression outcomes was anticipated. Using G*Power 3.1, calculations were conducted with an alpha of 0.08 and power of 0.95.

To ensure a robust design, feasibility thresholds were also defined according to Rossouw and Fonagy: recruitment ≥60%, retention ≥50%, and adherence ≥70%. These benchmarks provide a practical foundation for determining whether progression to a larger randomized controlled trial (RCT) is warranted.

 Data analysis

Quantitative analysis

Descriptive statistics will be used to characterize participants’ sociodemographic background and baseline clinical measures. Primary feasibility outcomes (recruitment, attrition, follow-up, and adherence rates) will be summarized using proportions with 95% confidence intervals. Acceptability outcomes from the CEQ will be analysed descriptively.

For secondary clinical outcomes (symptoms and family cohesion), multilevel modelling will be applied to account for therapist clustering and the longitudinal structure of the data. Comparisons will be conducted across baseline (T0), post-intervention (T2), and follow-up (T3). Effect sizes (Cohen’s d) will be calculated to inform the design of a larger RCT.

Session-by-session monitoring data (CORE-OM, YP-CORE-OM) will be summarized with descriptive statistics and visualized as trajectories of change. All quantitative analyses will follow a per-protocol approach 58 and will be performed in Stata 18 ®.

Qualitative analysis

Qualitative data from interviews with adolescents, caregivers, therapists, and supervisors will be analyzed using thematic analysis. 67 Coding will be carried out collaboratively by a pair of trained coders, who will work together throughout the process to identify patterns and themes. Atlas.ti software will be used to manage and organize the data. Triangulation across participant groups will be applied to enhance the trustworthiness of the findings, although no participant validation (member checking) will be conducted.

 Dissemination

The trial is prospectively registered at ClinicalTrials.gov (NCT06252090). No financial compensation is provided to participants or their families. Results will be disseminated through peer-reviewed publications, presentations at national and international conferences, and feedback reports to participating centers. Findings will also be shared with healthcare providers and policymakers to inform the adaptation and scaling of mentalization-based interventions in the Chilean public health system.

 Study status

The project is currently undergoing participant recruitment, and data collection is in progress.

 Discussion

This protocol describes a feasibility and acceptability study of short-term mentalization-based treatment for adolescents (MBT-A) diagnosed with mild to moderate depression. Beyond symptom management, adolescent depression requires attention to neurodevelopmental processes that shape emotional regulation and stress adaptation. A mentalization-based approach targets structural functions that are especially vulnerable during adolescence, helping reduce relapse risk and potentially interrupt intergenerational transmission of depression. 59

Incorporating the family is a key element, given the role of attachment relationships in the development of neurobiological systems involved in affect regulation and self-organization. 60 Family involvement enhances the maintenance of therapeutic change and may contribute to the prevention of future episodes. 61 While MBT has demonstrated efficacy for self-harming adolescents, 26 few studies have specifically focused on depression as the primary diagnosis while integrating a family-based approach. 62

Consistent with CONSORT guidance, 39 the primary aim of this pilot is to establish feasibility parameters for a future randomized controlled trial (RCT), while the secondary aim is to explore preliminary clinical outcomes. Data on feasibility, acceptability, and effect size will serve as benchmarks for designing and powering a definitive trial. Conducting a pilot is particularly important given that depression is associated with high dropout rates in psychotherapy, both before and during treatment, especially in outpatient contexts. 63 Maintaining family adherence is another challenge this study seeks to address.

This study has several strengths, including its adaptive design, which allows for adjustments to intervention delivery or evaluation procedures according to participants’ needs. Combining quantitative outcomes with adolescents’ qualitative evaluations will provide a richer understanding of feasibility and acceptability and will support culturally sensitive adaptations.

Limitations should also be acknowledged. The single-arm design without a control group limits conclusions about efficacy. Recruitment biases are possible, given the high comorbidity of adolescent depression with other psychiatric disorders. 64– 66 In addition, variability in therapist training and the intensity of supervision may introduce sources of bias.

Despite these limitations, this study represents an important step toward adapting and testing MBT-A in Latin America. Findings will inform the design of a larger RCT and contribute to the development of evidence-based, family-inclusive psychotherapies for adolescent depression.

 Ethical considerations

This study was approved by the Institutional Ethics Committee of the University of Valparaíso (CEC-UV 262-22). All procedures comply with the Declaration of Helsinki and national ethical standards.

Potential participants will first be approached by their treating healthcare provider, who will consult with caregivers regarding the possibility of being invited to the study. If caregivers express interest, the healthcare provider will inform the principal investigator. The principal investigator will then contact the family to explain the study in detail, including procedures, and extend a formal invitation. If the family agrees to participate, written informed consent will be obtained from caregivers and assent will be obtained from adolescents before any study activities begin. Participants will be informed of their right to withdraw from the study at any time without consequences for their usual care.

The trial is coordinated by the research team at the University of Valparaíso. Data collection and management are overseen by the principal investigator and research staff, following protocols approved by the Institutional Ethics Committee. No external steering committee or endpoint adjudication committee was established, given the exploratory nature of this feasibility pilot.

Reporting guidelines

Zenodo: The SPIRIT checklist for Study Protocol: Single-Arm Pilot Feasibility of a Short-Term Family-Based Mentalization Approach for Early Adolescents with Depression 10.5281/zenodo.17501670. 68

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).

 Data availability statement Underlying data

Zenodo: Short-Term Family-Based Mentalization Approach Pilot Study. 10.5281/zenodo.17501670. 68

This project contains the following underlying data:

F1000 flow chart.tif (flow diagram illustrating study design)

 Extended data

No extended data associated with this article.

 Acknowledgements

We would like to sincerely thank Dr. Efrain Bleiberg for his valuable suggestions and guidance throughout this project.

This protocol has also been made available as a preprint: Morán-Kneer J, Duarte J, Alkabes-Esquenazi L, Solervicens P, García F, Arancibia M, Díaz F, Avalos N. Protocol for the feasibility and acceptability of mentalization-based treatment for early adolescents with depression: a short-term psychotherapy approach for patients and families. medRxiv. 2024 Oct 15;2024.10.15.24315540. doi: https://doi.org/10.1101/2024.10.15.24315540. 69

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