Currently, treatments for mucopolysaccharidoses (MPS) are pharmacological and predominantly focus on the physical symptoms of the disease. In the general population and individuals with disabilities, increasing physical activity levels and reducing sedentary time can be an effective, non-pharmacological treatment to improve mental health and quality of life. Such interventions have not yet been developed or evaluated in people with MPS.

The aim of this study is to co-design a physical activity and sedentary behaviour intervention tailored to the needs of adults with MPS. The study will seek to gain the expertise of adults with MPS, specialist stakeholders (physicians and clinical nurse specialists) and lay specialist stakeholders (family and friends of adults with MPS and members of staff and volunteers at the Society for Mucopolysaccharide Diseases). A range of views and experiences of physical activity and sedentary behaviour will be explored via focus groups (with individuals with MPS and lay specialist stakeholders) and semi-structured interviews (with specialist stakeholders). The information gathered from the focus groups and interviews will then be utilised to inform participatory workshops (with individuals with MPS) to test intervention concepts. Data from these activities will inform the design of a future intervention.

Adults with Mucopolysaccharidosis will be eligible to participate in the study if they meet the following inclusion criteria:

• Diagnosed with any type of Mucopolysaccharidosis.
• Aged ≥ 18 years old.
• Lives in the United Kingdom.
• Deemed safe to participate by a clinician (for participatory workshops).

Exclusion criteria for all participants will be as follows:

• Incapacity to provide informed consent.
• A level of intellectual disability that would prevent the individual from making a meaningful contribution to the focus groups or workshops.
• Unable to communicate in English to a sufficient level to permit engagement in the study.

The circumstances in which an individual may be deemed ineligible to take part in the participatory workshops based on the clinician's assessment are as follows:

• Severe joint pain.
• Neurological compromise.
• Stage 4 heart failure or other condition resulting in breathlessness to a level they cannot participate.
• Other clinical condition which dominates the clinical picture to the extent that it dominates the symptoms and influences the findings (e.g. stroke).

Specialist stakeholders will be members of staff at NHS specialist centres for Mucopolysaccharidosis who are directly involved in healthcare provision to the target population.

Lay specialist stakeholders will be individuals who have been involved in supporting adults with Mucopolysaccharidosis, such as family, friends, and members of staff and volunteers at the Society for Mucopolysaccharide Diseases.

Adults with Mucopolysaccharidosis, lay specialist stakeholders and specialist stakeholders who meet the eligibility criteria.