Assessing disease progression in spinal muscular atrophy, current gaps, and opportunities: a narrative review

Spinal Muscular Atrophy is a genetic disorder causing muscle atrophy and progressive weakness. People living with the condition can have a significant heterogenous phenotype ranging from arrest of motor development to mild impairment. Assessing disease severity has been done using a range of outcome measures that can be classified by body structure or function, by activities or by participation. Functional outocome measures can be generic measures, used to compare individuals or populations against general norms, or disease-specific measures designed to fit disease characteristics. Outcome measures assessing participation are primarily used to capture patients' perceptions of health-related quality of life, daily activity abilities, caregiver burden, and the impact of physical symptoms like fatigue or pain. When assessing disease progression, often the focus on functional abilities has served as an overall indicator of change. With the appearance of disease modifying therapies and the need to evaluate the impact that they had in the course of the disease, new requirements for the existing assessments measure had appeared. The current available toolkit is able to capture a significant spectrum of both, natural history and effect of new treatments but the increased survival, changes in fatigue, bulbar function and others will benefit from further assessment.