With this work, the Rare Bone Disease action group of ECTS provides a DELPHI consensus on TC for young persons with a RBMC. This Delphi consensus reflects expert opinion and offers an important first step toward standardized transition care in RBMCs. Future empirical studies are needed to assess the real-world impact and feasibility of these recommendations.

To our knowledge, these are the first recommendations for RBMC TC services. While there are some expert consensus recommendations for specific RBMCs e.g. for osteogenesis imperfecta [17] and XLH [14], there are none which provide guidance for Departments and Services tasked with managing persons with a spectrum of different RBMCs. Of note, the consensus recommendations presented here align with key transition care principles described in the Asia–Pacific consensus on XLH [14] and the EULAR/PReS recommendations for juvenile-onset rheumatic diseases [15]. However, our work specifically addresses the complexity and variability of RBMC, emphasizing individualized timing, multidisciplinary input, and condition-specific challenges not fully captured in these prior frameworks.

We originally opted against conducting a survey on current TC practices as done by Casado et al. [11] and Shishkov et al. [21] as TC is underfunded in most countries [22] and thus current practice will represent local solutions that are highly dependent on the interest and motivation of individual clinicians, the size of the Hospital Department unit available resources.

One of the crucial points in undertaking a Delphi survey lies in the selection of the expert panel members who participate in the anonymous and non-anonymous voting process of the Delphi [19, 23]. Accordingly, we have combined patient representation of three major RBMCs, and clinical experts (> 10 years of clinical experience in the field) from different disciplines from pediatric and adult care and representing different European countries.

Despite the heterogeneity of background, the panelists, there was high consensus on most statements that were generated, indicating that experts and patient representatives had a similar understanding of the requirements of TC.

The consensus derived for TC for young persons with RBMCs here, importantly reflects the recommendations of the twelve European League Against Rheumatism (EULAR) standards and recommendations for the TC of young persons with juvenile-onset rheumatic diseases [15].

We, like others, have concluded that effective TC should ensure both continuity of medical management and address the unique psychosocial aspects associated with chronic rare diseases. For young persons with RBMCs, timely initiation of the TCP, starting as early as by age 12–14, or when transition readiness is established [24], has been shown to improve readiness for transfer to adult services and decrease potential gaps in care. Several validated tools, such as the Transition Readiness Assessment Questionnaire (TRAQ) [24] and the web-based toolbox ‘Got Transition’s Six Core Elements of Health Care Transition™ ‘ (Got Transition Resources) offer structured approaches to transition, and customizable tools for assessing readiness, planning, and transfer of care. While not developed specifically for RBMCs, they can be adapted to this population with condition-specific modifications. Implementing a structured transition with clear role assignments within the TCT helps optimize communication between pediatric and adult providers and facilitates individualized care planning [25, 26].

These consensus recommendations have highlighted the importance of fostering empowerment of the young person with a RBMC, which is a dynamic process encompassing education, self-advocacy, and community integration. These elements collectively empower young persons as they navigate the complexities of these rare conditions and have been described previously for other rare diseases as well [8, 25].

Providing access to peer support networks and resources is particularly effective in enhancing resilience and confidence during the TCP [27]. However, it should be mentioned that peer support groups are often led by older adults and may not have a young person’s group, which may limit the attractiveness of patient groups to adolescents and commonly have limited representation of ethical minorities which may limit the group's attractiveness to younger participants from various backgrounds.

Despite the agreement on many aspects of the TCP, the variability in healthcare systems across Europe will challenge any uniform implementation of TC guidelines [5, 28]. Our consensus recommendations underline the importance of integrating legal, cultural, and financial considerations specific to each country into the TC framework. For example, disparities in funding and availability of transition-specific resources may limit the consistency of care across regions, suggesting a need for flexible but standardized TCP frameworks to bridge these differences. Particular challenges exist in low-resource healthcare systems, where infrastructure and funding constraints may limit implementation. Approaches such as stepwise integration, use of digital platforms, or adaptation of essential elements of care may enhance feasibility. Barriers to implementation may also include lack of formal reimbursement for transition care coordination roles, limited institutional support for cross-specialty meetings, and low levels of engagement from adolescents or families unfamiliar with long-term care planning. Identifying scalable, sustainable models is critical for broader implementation. Based on the consensus process, we suggest that transition programs for RBMCs should aim to implement a minimum standard of care regardless of local resources or specific diagnosis. This includes: A designated transition coordinator or contact person and an individualized written care plan shared with the adult team. These elements could serve as measurable benchmarks across diverse healthcare settings.