Gross motor functional classification for arthrogryposis multiplex congenita: protocol for co-development involving public with lived and professional experience

Abstract

Background

Children with arthrogryposis multiplex congenita (AMC), a group of over 400 conditions characterized by congenital joint contractures, present with a wide range of gross motor functioning and mobility due to the heterogeneity of underlying diagnoses and physical involvement. Existing classification systems for AMC focus primarily on etiology and anatomical distribution but do not describe differences in gross motor functioning. In contrast, condition-specific functional classification systems have improved communication, treatment planning, and research by stratifying individuals based on functional ability. To date, no such classification system exists for AMC. This study aims to co-develop and evaluate the Gross Motor Functional Classification for Arthrogryposis Multiplex Congenita (GMFC-AMC), a condition-specific tool to support clinical and research needs.

Methods

This multi-phase study involves stakeholders with lived and professional experience in AMC from multiple countries. Phase 1 includes the initial drafting of the GMFC-AMC by an expert panel. In Phase 2, nominal group techniques are used to refine the draft. Phase 3 employs Delphi surveys to achieve international consensus on relevance, clarity, and comprehensibility. In Phase 4, the GMFC-AMC is translated and culturally adapted into French and Spanish following a structured cross-cultural adaptation process. Finally, Phase 5 evaluates reliability and construct validity across three languages. Inter-rater and test-retest reliability will be examined using video ratings of children with AMC. Construct validity will be assessed through correlations with established measures, including the Gillette Functional Assessment Questionnaire and the Pediatric Evaluation of Disability Inventory – Computer Adaptive Test.

Discussion

The GMFC-AMC will address a critical gap in functional classification for children and youth with AMC by providing a standardized language for describing gross motor functioning. By engaging international stakeholders throughout the development process and ensuring rigorous testing of its psychometric properties, the GMFC-AMC is expected to be a reliable, valid, and meaningful tool across diverse clinical and cultural contexts. This classification will facilitate clearer communication, improve care planning, and enable stratification for future longitudinal and interventional studies in AMC populations.

Trial registration

Clinical trial number not applicable.

Background

Much of clinical care for children with physical disabilities focuses on assessing and enhancing their mobility and functional abilities. But when a child presents with a mobility phenotype that exhibits a high degree of heterogeneity throughout the population, communication between healthcare providers is hindered by a lack of precise, standardized terminology. Similarly, investigating the factors that influence the differences in motor ability, and the efficacy of treatments for different manifestations of the phenotype, relies on the ability to stratify patients into relevant groups. Arthrogryposis multiplex congenita (AMC) is one such heterogeneous phenotype [1] that would benefit from a common language to more precisely characterize a patient’s level of gross motor functional abilities and capture the wide range of mobility strategies, adaptive methods, and performance patterns observed in this population, thereby clarifying what an individual with AMC does and how they function within their current environment [2, 3].

Over the past 30 years, clinicians and researchers have standardized the terminology used to describe different levels of motor function for various patient populations by developing classification systems based on simple ordinal scales [4–8]. These systems consider a combination of physical abilities and use of adaptations specifically relevant to the population under study to stratify patients into meaningful and informative levels of mobility. A classification system describes what level of functioning a person belongs to, while an outcome measure determines how much ability a person has or how it changes over time [2]. One of the most widely used classification systems is the Gross Motor Function Classification System (GMFCS), designed to describe the functional abilities of children with cerebral palsy (CP) [4–8]. Before its development, CP was mostly classified based on motor type (e.g., spastic, hypotonic, ataxic, dyskinetic, mixed) and topographical distribution (e.g., di-, tri-, tetra-, quadri-, hemiplegia), with severity often described subjectively as mild, moderate, or severe [5]. While common at the time, this terminology created broad categories that made communication imprecise and provided little information about functional abilities [5]. In contrast, the GMFCS provides clear distinctions on the performance of age-appropriate activities across five levels [5–8]. Since its introduction, the GMFCS has become the international standard for classifying motor function of children with CP in clinical practice and research [5–8].

The widespread use of the GMFCS highlights a recognized need for systems that classify gross motor function in children with conditions other than CP [9], such as autism [10] as well as in rare diseases [11]. Since functional classifications have been widely used in research and clinical practice for treatment planning, prognosis, and clinical decision-making [8], Kehrer and colleagues (2011) adapted the GMFCS development framework to create the Gross Motor Function Classification for children with metachromatic leukodystrophy (GMFC-MLD) - a rare inborn error of metabolism characterized by early and progressive loss of cognitive function and gross motor abilities [11]. The GMFC-MLD demonstrated high reliability and construct validity, making it a valuable tool for the standardized and broad classification of gross motor function in individuals with MLD [10]. Moreover, caregivers have found the GMFC-MLD to be both interpretable and meaningful in capturing the physical declines experienced by their children [12]. The GMFC-MLD exemplifies how a condition-specific functional classification system for children with a rare disorder can enhance understanding of disease presentation by clarifying phenotypic spectrums. Such systems can support improved clinical care, inform the design of prospective natural history studies, and facilitate the stratification of patient cohorts for clinical trials [13]. A similar approach would be beneficial for children and youth with AMC [14] .

AMC is a term used to describe a group of over 400 developmental conditions characterized by joint contractures in two or more body areas at birth, resulting from reduced or absent fetal movements. Despite this common pathogenic mechanism of reduced movement, these disorders arise from a wide range of etiologies, including central nervous system disorders, neuromuscular diseases, exposure to teratogens, maternal illness, or limited space in utero [15, 16]. Correspondingly, the clinical presentation of disorders involving AMC is also highly heterogeneous. Depending on the underlying diagnosis, other body systems such as the central nervous system (CNS), respiratory, gastrointestinal, and genitourinary systems may be affected, and prevalence of intellectual disability among these syndromes ranges from 25% to 30%, often resulting in severe functional impairments [16–18].

Focusing on the AMC phenotype, the severity and distribution of the contractures themselves can vary greatly as well, resulting in a wide range of functional abilities. In their updated definition of AMC, a panel of experts stated that “individuals with AMC have limited joint movement, with or without muscle weakness, in the involved body areas.” [15] Restricted joint movement can cause abnormal connective tissue formation around the joint, leading to stiffness that further reduces muscle use, contributes to fibrosis, and ultimately results in muscle weakness and the formation of contractures [19–21]. The joints affected vary from patient to patient, as do the extent of the contractures and the degree of accompanying muscle weakness, and these differences have real impacts on the treatment plan. With this high degree of heterogeneity, each patient must be individually assessed and provided with a tailored plan. Treatment options range from conservative methods, such as nonsurgical interventions, to surgical procedures, with the shared goal of enhancing mobility and functional abilities [19–21]. The limitations in joint movement and muscle weakness may restrict the ability to perform everyday activities (e.g., eating, dressing, walking), and participation is variable, requiring multidisciplinary care [22, 23].

Children and youth with AMC present a wide range of functional abilities shaped by the severity and distribution of joint contractures, muscle weakness, and limb deformities [24]. Recent studies show that while many children achieve some level of ambulation - typically on level surfaces and short distances - mobility decreases with more complex environments, and alternative strategies such as scooting, wheelchair propulsion, or reliance on aids are common [24]. Their functional repertoire similarly varies, with substantial challenges in daily activities and dressing tasks and mobility scores [25] that fall well below typically developing peers [26], underscoring the importance of a classification system that captures these nuanced, AMC-specific functional patterns.

Classification systems play a crucial role in diagnosis, communication, treatment planning, and prognosis. Therefore, various approaches have been proposed [27, 28]. However, the development of classification systems for AMC has been challenging, specifically because of this phenotype’s wide range of manifestations and underlying causes [14, 27–29]. The most widely used classification systems for AMC categorize the condition based on (1) the extent of body system involvement (i.e., limbs only, limbs and other systems, limbs and CNS involvement), (2) the etiology of fetal akinesia (i.e., intrinsic fetal conditions; extrinsic factors like restricted intrauterine space; environmental factors such as maternal illness or teratogenic exposures), or (3) key clinical features (i.e., Amyoplasia, distal arthrogryposis, CNS/syndromic forms) [27, 28]. Although these classification systems provide important information to understand the scope of anatomic system involvement and etiology, their clinical contribution remains limited [14, 29]. Moreover, despite these classification frameworks, there is significant heterogeneity in gross motor function even within sub-groups, highlighting the need for an AMC-specific functional classification system to better understand gross motor function performance in real-life contexts [12, 29]. Thus, the overall aim of this project is to co-develop a Gross Motor Functional Classification for children and youth with AMC, involving stakeholders with lived and professional experience, to translate and cross-culturally adapt the classification into French and Spanish, and to evaluate its validity and reliability across languages and contexts.

Methods/Design

Study design

This project will employ a multi-phase methodology consisting of the five following phases described below (Fig. 1).

Fig. 1.

Study flow

Phase 1 will consist of developing the content and drafting the GMFC-AMC utilizing several remote and in-person meetings.

Phase 2 will use nominal groups conducted remotely to refine the draft GMFC-AMC.

Phase 3 will comprise Delphi surveys to obtain international consensus on the proposed GMFC-AMC.

Phase 4 consists of translating and culturally adapting the English version of the GMFC-AMC to French and Spanish.

Phase 5 will ascertain the reliability and validity of the new classification in all three languages.

Patient and public involvement

The research team is composed of clinicians specializing in occupational therapy, physical therapy, physical rehabilitation medicine, orthopedics, and neurology, as well as people with lived experience, representing five countries. This team is involved in the development and dissemination of the GMFC-AMC. Once the development phases of the GMFC-AMC are completed, it will be translated and culturally validated to other languages represented in our research team’s scope. The GMFC-AMC will be disseminated to the AMC community internationally via publications, infographics and other knowledge translation media, and through national AMC support groups, websites and social media (e.g., Arthrogryposis Multiplex Congenita Support, Inc.).

Study procedures

Phase 1. Content co-development

An expert panel composed of individuals with experience in AMC and motor assessment (e.g., physical and occupational therapists, orthopedic surgeons, physiatrists, orthotists, adults with AMC, parents of children with AMC) will draft an initial version of the GMFC-AMC. The expert panel will include clinicians with at least two years of experience providing care to the AMC population, individuals with AMC 18+ years old, and/or parents of children from 2 to 18 years old with AMC, as this is the initial age range for which the classification will be developed. They will be identified through our international AMC consortium and network of experts and will be invited through an informative email containing specific details on the project. Further emails will be sent to schedule the meetings. We expect up to 15 participants for this phase, which aligns with recommended sample sizes for qualitative and consensus-building work where 10–15 purposively selected individuals are typically sufficient to capture diverse perspectives and reach conceptual saturation, and plan for approximately 50–60% rehabilitation and medical professionals, 30–40% people with lived experience or family members, and 10–20% researchers [30, 31]. The expert panel will meet to develop this first draft using literature reviews on gross motor function in AMC and their experience in real life situations. The draft will be revised during those meetings, as well as email exchanges, using a dynamic process of construct development. A conceptual background using a hierarchical model to define levels of gross motor function, incorporating the key elements of independence (i.e., use of aids/assistive devices) and external support (i.e., need for assistance/aids), will be central to the draft development. We anticipate this to be an iterative process in which the group will collectively determine when the initial draft is sufficiently refined to proceed to Phase 2, which will then be evaluated by the nominal groups in phase 2. Up to ten meetings lasting between 90 and 120 minutes each will be conducted using a secure and approved virtual platform. The meetings may be recorded to facilitate the analysis of the content shared. After participation in the drafting meetings, information about the expert panel characteristics (e.g., country, expertise, years of experience) will be collected via email. A form will be completed for this purpose or may be completed by the clinical research coordinator (CRC).

Phase 2. Content refinement

The use of nominal group technique (NGT) will facilitate discussions among individuals with the purpose of creating a consensus opinion [31]. We aim to recruit approximately 25 participants, consistent with methodological guidance for conducting multiple small NGT groups of 5–9 participants each [32]. We anticipate a composition of roughly 60–70% rehabilitation/medical professionals/researchers, 30–40% people with lived experience or family members, ensuring representation while maintaining manageable group dynamics in a rare disease context. We will include clinicians with at least two years of experience providing care to the AMC population, individuals with AMC 18+ years old, and/or parents of children from 2 to 18 years old with AMC. We will email the GMFC-AMC draft 1 week before the nominal group meeting and invite participants to prepare comments and suggestions for potential changes. Participants will be encouraged to engage in discussions, ask questions, and analyse and incorporate ideas and suggestions. Changes will be made to ensure the GMFC-AMCs purpose, content, appropriateness, and clarity by asking participants to vote on the changes until consensus is reached. Each meeting will last between 90 and 120 minutes using a secure and approved virtual platform. The on-line meetings may be recorded to facilitate the analysis of the content shared. After participation in the nominal groups, information on participants (e.g., country, expertise, years of experience) will be collected via email. A form will be completed by participants for this purpose or may be completed by the CRC.

Each group session in phases 1 and 2 will be guided by a trained facilitator to ensure structured, balanced, and effective discussion.

Phase 3. International consensus approach

Participants for this phase will include international experts in AMC in the fields of rehabilitation, orthopedics, pediatrics, physiatry, neurology, genetics, and individuals with lived experience, following the same eligibility criteria from the previous phases. We expect up to 45 participants for this phase, which reflects the recommended double-digit panel size (30–50) often considered optimal in Delphi concluding rounds [32], balancing methodological rigour with the practical constraints and limited pool of experts inherent to research in a rare condition such as AMC. The structure of Delphi surveys provides the ideal methodology to enable stakeholders to share feedback anonymously [32–35]. The purpose of this phase is to achieve consensus on the relevance, clarity, and comprehensibility of the GMFC-AMC by a large number of experts. Participants will be asked to rate their agreement with each sentence on a 5-point Likert scale (1 = strong disagreement to 5 = strong agreement) and provide comments using a Shriners’ approved survey platform. An 80% agreement level (% of ratings ≥ 4 on the 5-point scale) will be used; subsequent survey rounds will focus on 1) rewording and rethinking elements that have not reached sufficient agreement and 2) discussing comments regarding content and formatting. We anticipate three rounds of this modified Delphi approach, with participants from round 1 being invited to round 2, and so forth. Each survey is expected to take about 30–45 minutes to complete. Demographic data on the participants in this phase will be ascertained using the Delphi questionnaire survey (e.g., country, expertise, years of experience).

Phase 4. Translation and cross-cultural adaptation for French and Spanish versions

Cross-cultural adaptations will follow the five stages recommended by Beaton and colleagues [36], while also aligning with recent practical guidelines that endorse coordinated multilingual strategies as a valid and often necessary approach when instruments are intended for use across multiple linguistic contexts [37, 38]. In Stage I, the classification will be translated (forward-translation) by two pairs of independent translators (one clinically informed translator and one naïve translator) whose native language is each of the targeted languages (French and Spanish) and who are fluent in English (the original language of the classification). In Stage II, the two translations of each targeted language will be synthesized to create a single translation (one final translation in French and Spanish). In Stage III, the synthesized versions of the GMFC-AMC will be back-translated into English by a native English speaker fluent in these languages, who has no knowledge of healthcare or the classification in question. This version will be reviewed by the primary authors of the GMFC-AMC for a final revision to ensure consistency.

After approval of this version, in Stage IV, two expert committees - one per language (French and Spanish), each with up to 10 members - will review and confirm the equivalence of the translated versions; this group size aligns with consensus-building guidelines, where this number of purposively selected individuals are typically sufficient to ensure diverse perspectives and reach conceptual saturation. Committee members will include professionals in physical therapy, occupational therapy, and medicine specializing in pediatrics and neuromusculoskeletal conditions, as well as individuals aged 18 + old with AMC and caregivers of children with AMC aged 2 to 18 years. The committees will receive the translated versions to ensure that the terms are clear and familiar. Tables containing the original sentences and their respective translations will be sent to each expert for analysis of the conceptual equivalence and cultural appropriateness of each sentence in French and Spanish. The experts will receive specific instructions to evaluate each sentence of the instrument. They will be asked to indicate whether the English and French/Spanish versions convey the same meaning, assessing the conceptual equivalence. They will also be asked to determine whether the French/Spanish sentences will be understandable (comprehensibility) and whether the terms used are relevant for the target populations and context, addressing cultural adaptation [36–38]. Additionally, experts will be invited to provide suggestions for changes in the “comments” column, if applicable. Experts’ responses will be recorded with a score of 0 assigned to “no” answers and 1 to “yes” answers, for both the assessment of conceptual equivalence and cultural adequacy. The level of agreement will be calculated as the percentage of “yes” responses for each item. A concordance rate of 90% or higher is considered acceptable [39, 40]. Suggestions from the expert committee will be used to revise items that fall below this threshold. Qualitative feedback will be gathered from interviews with the experts to ensure rigorousness [40] Fig. 2.

Fig. 2.

Translation and cross-cultural adaptation for French and Spanish (study phase 4)

Phase 5. Reliability and construct validity of the GMFC-AMC versions (English, Spanish, and French)

To ensure consistent observation, videos of children performing selected activities will be recorded following standardized instructions. During data collection, one clinician will administer and score the GMFC-AMC in-person, while the remaining raters will classify the gross motor function of the same children using the video recordings. Raters will be asked to watch the recordings and rate the GMFC-AMC level using the age-appropriate version of the classification, administered in the language-appropriate version to ensure clarity and cultural relevance. To standardize the analysis of gross motor function, all children will be videotaped during routine mobility activities (i.e, rolling, crawling, floor mobility, walking, navigating stairs, running, jumping) to capture each child’s typical means of mobility - indoors and outdoors - using assistive devices if applicable (e.g., canes, crutches, walkers, wheelchairs). The video protocol will ensure observation of moving, walking on flat surfaces, navigating stairs or steps (with or without railings), and transitioning between positions (e.g., sit to stand, floor to standing). The standardized recording protocol is intended only to ensure good-quality, comparable video footage across sites. Children will move as they typically do in daily life, using their usual strategies and assistive devices. The procedures ensure clarity of observation while preserving the performance-based nature of the GMFC-AMC. Clinical research coordinators (CRCs) will be trained to complete recordings within a single site visit, minimizing burden for participants and families.

Raters will include occupational therapists, physical therapists, orthopedic surgeons, and/or kinesiologists, each with a minimum of one year of experience working with children with musculoskeletal conditions. Children eligible for inclusion will be between 2 and 18 years of age, with a confirmed clinical diagnosis of AMC, and receiving care at one of the participating hospital sites within Shriners’ Children. A virtual training module will be delivered by the developers of the GMFC-AMC (CA and ND-O) to all site investigators and clinicians. These sessions will be conducted using a teleconferencing platform (e.g., Microsoft Teams), last approximately two hours, and cover administration and scoring procedures for the GMFC-AMC.

Inter-rater reliability

To assess the inter-rater reliability, an ordinal scale with the GMFC-AMC levels will be used to calculate weighted kappa coefficient with quadratic weights. At least four raters (up to 16, with two per participating site) will be asked to rate each video using the age-appropriate GMFC-AMC, resulting in unique pairwise comparisons per child, to detect agreement (Cohen’s κ interpreted according to: < 0.00 = poor, 0.00–0.20 = slight, 0.21–0.40 = fair, 0.41–0.60 = moderate, 0.61–0.80 = substantial, and 0.81–1.00 = almost perfect agreement) [41–43] with a 95% confidence level and 80% statistical power. To account for potential data loss (e.g., missing data, discrepancies requiring exclusion, or technical issues during data collection), a 20% safety margin will be added. Accordingly, power calculations indicate that roughly 30 children are needed, and applying the 20% safety margin results in a final target sample of 36 children.

Given that AMC is a rare condition, using at least four raters per child maximizes the number of pairwise comparisons and meets methodological recommendations for obtaining stable estimates [41–43]. Increasing the number of raters is often more practical and statistically advantageous than increasing the number of subjects, as additional raters substantially improve the precision of kappa while remaining feasible in a multi-site study [41–43].

Test-retest reliability

To assess the temporal stability of the GMFC-AMC, test-retest reliability will be conducted with a subset of children. The sample size will be determined based on methodological recommendations for reliability studies, which commonly include 10 to 30 participants for preliminary evaluations [41–43]. Two raters will independently re-classify the gross motor function of the same children using the GMFC-AMC after an interval of approximately 14 to 30 days. This timeframe is expected to be short enough to avoid meaningful changes in gross motor function. Agreement between the initial and follow-up classifications will be evaluated using weighted Cohen’s kappa (with quadratic weights), and 95% confidence intervals will be calculated to assess the precision of the reliability estimates. This analysis will provide evidence of the temporal consistency of the GMFC-AMC classifications and inform its use in both clinical and research settings.

Construct validity

To assess the construct validity of the GMFC-AMC, a correlational analysis will be conducted comparing GMFC-AMC levels with scores from two established measures: the Gillette Functional Assessment Questionnaire (FAQ) [44, 45] and the Pediatric Evaluation of Disability Inventory – Computer Adaptive Test (PEDI-CAT) [46, 47]. These instruments are selected for their relevance in assessing mobility and function in pediatric populations. The sample size will be determined to detect a moderate correlation (r = 0.5) with 95% confidence and 80% power. A 20% safety margin will be added to account for potential data loss. The GMFC-AMC level, FAQ scores, and relevant PEDI-CAT domain scores (e.g., mobility, daily activities) will be collected concurrently. PEDI-CAT will also be used to characterize children’s functional independence in daily activities and mobility. The PEDI-CAT is a validated, standardized measure that has demonstrated meaningful differentiation of functional profiles in children with AMC [25]. Linking the GMFC-AMC levels to PEDI-CAT will allow us to explore expected differences in functional independence, consistent with approaches used in other functional classification systems. In addition, we will compare PEDI-CAT Mobility scores and FAQ walking ability scores across GMFC-AMC levels to further evaluate construct validity. This combined approach enables us to assess whether higher GMFC-AMC levels align with systematically lower functional performance, thereby supporting the validity and clinical interpretability of the classification. Spearman’s rank correlation coefficients will be calculated to examine associations among these instruments. PEDI-CAT domain scores across GMFC-AMC levels will be evaluated using analysis of variance (ANOVA). Post hoc pairwise comparisons between patients with different GMFC-AMC levels will be conducted with multiple comparison adjustment for p values. This analysis will help determine the extent to which the GMFC-AMC is aligned with existing validated measures of pediatric mobility and participation, providing initial evidence of its construct validity.

Ethics and dissemination

Administrative site approval was obtained from the Department of Medical Research at the Shriners’ Children (CAN2302). Research ethics approval was obtained from the Faculty of Medicine and Health Sciences Institutional Review Board (IRB) at McGill University (IRB internal number A03–M11-23A) and was deemed to involve no more than minimal risk (phases one to three). Patient participation will be completely voluntary, and informed consent will be obtained prior to participation in Phases 3 and 5. Electronic consent will be obtained prior to completing the surveys for phases 3. Signed written consent will be obtained for phases 4 and 5.

To support the dissemination and implementation of the GMFC-AMC and promote consistency across clinical and research settings, we will develop a set of open-access materials that will be made available through an institutional repository. These materials will include the guide to use the classification describing the conceptual framework, instructions, distinctions between levels and operational definitions of terms and concepts used to develop the tool, and case examples; and translation tables documenting cross-cultural adaptation procedures for the other versions.

Capacity-building materials will be developed to ensure the reliable application of the GMFC-AMC. These will include short instructional videos demonstrating classification across levels, recorded webinars, and a self-paced online training module with case-based exercises. We will additionally provide templates to support implementation in clinical workflows and research studies. Lay-oriented materials (such as infographics and accessible summaries) will also be developed to support dissemination among families, patient advocacy groups, and community organizations, and may be shared through social media platforms and partner websites. Together, these openly available materials will facilitate implementation, enable replication in future studies, and support broader knowledge translation in this rare condition.

Discussion

This protocol outlines a rigorous multi-phase approach for the co-development of the GMFC-AMC, addressing a critical gap in functional classification for this population [14, 29]. While existing classification systems provide valuable information regarding anatomical involvement and etiology, they do not capture variations in gross motor function - particularly within subgroups defined by phenotype or diagnosis. By involving stakeholders with both lived and professional experience across all phases, the resulting classification will have the potential to be both clinically meaningful and grounded in the real-life contexts of children with AMC [48–50].

The multi-phase methodology including initial drafting, refinement through nominal groups, consensus-building via Delphi surveys, and cross-cultural adaptation reflects a commitment to participatory and inclusive research. These strategies are essential for developing a classification tool that is acceptable and applicable across different languages, cultures, and healthcare settings and are important steps for extending its relevance, usability and implementation in diverse global contexts in the future [2, 3]. Finally, the planned evaluation of the GMFC-AMCs reliability and validity will provide preliminary evidence of its measurement properties. This includes assessing inter-rater and test-retest reliability as well as content validity. These efforts will support the GMFC-AMCs use in clinical, research, and program evaluation settings, facilitating more precise communication among professionals and better-informed care planning for children with AMC. Ultimately, this work lays the foundation for future studies examining longitudinal outcomes and intervention effectiveness using a functional lens.

Abbreviations

AMC

Arthrogryposis multiplex congenita

GMFC-AMC

Gross Motor Functional Classification for Arthrogryposis Multiplex Congenita

GMFCS

Gross Motor Function Classification System

CP

cerebral palsy

GMFC-MLD

Gross Motor Function Classification for children with metachromatic leukodystrophy

CNS

central nervous system

CRC

clinical research coordinator

FAQ

Gillette Functional Assessment Questionnaire

PEDI-CAT

Pediatric Evaluation of Disability Inventory – Computer Adaptive Test.

Author contributions

ND-O and CRSA conceptualized and planned the study. CRSA and ND-O drafted the manuscript. LH, SES, CB, CC, DNB, MD, and AF contributed their professional expertise to the development of the initial draft of the functional classification and substantively revised the manuscript. KD, ME, and JCS contributed their lived experience with AMC, helped develop the initial draft of the functional classification, and were actively involved in drafting and revising the manuscript. All authors reviewed and approved the final version of the manuscript and agree to be personally accountable for their contributions and for ensuring the integrity of the work. ND-O, LH, and the AMC Registry Team contributed to the development of the study protocol and secured funding.

Funding

This project is funded by a Shriners Children’s Multisite Clinical Grant (#79137). Dr. Dahan-Oliel holds a Clinical Research Scholar Award from the Fonds de la recherche du Québec – Santé (FRQS). Dr. Araujo acknowledges the support of Shriners Children’s (2023-2024), and she holds a Post-Doctoral Fellowship in Child Health Research Excellence (2025), generously supported by the Montreal Children’s Hospital Foundation at the McGill University Health Centre - Research Institute. Dr. Araujo is supported by a Post-doctoral Fellowship from the National Council for Scientific and Technological Development (CNPq) -Brazil (Special Program for International Collaboration).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Administrative site approval was obtained for the study from the Department of Medical Research at SHC (CAN2302). Phases one to three obtained approval from the Faculty of Medicine and Health Sciences Institutional Review Board (IRB) at McGill University (IRB internal number A03-M11-23A) and was deemed to involve no more than minimal risk. Ethics review and approval were conducted in accordance with the Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans (TCPS2, 2nd Edition), the Cadre de référence ministériel pour la recherche avec des participants humains (MSSS, 2020), and the Food and Drugs Act (17 June 2001). The study also complies with the U.S. Code of Federal Regulations governing research on human subjects (Title 45 CFR 46; FWA 00004545) and adheres to internationally accepted principles of Good Clinical Practice and the Declaration of Helsinki. Informed consent was obtained from all participants. Ethics approval for phases 4 and 5 of the study will be obtained upon completion of phase 3, prior to the initiation of any further data collection.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.