Lysosomal storage diseases and related disorders (LSRDs) are a heterogeneous group of rare diseases caused by genetic mutations that result in deficiencies of specific lysosomal enzymes. Some of these enzymes are necessary for normal development of the central and peripheral nervous systems. Because of the heterogeneity in clinical presentation and complexity of these disorders, evaluation of disease progression poses unique challenges. In recent years, recombinant enzyme replacement therapy and haematopoietic stem cell transplantation have been developed to treat some of these diseases. With the development of specific therapies and screening programmes, there is a need to systematically follow the natural course and effects of treatment in these disorders with standardized and validated tools. This review describes the limitations of currently available neurobehavioural tools in longitudinally tracking disease outcomes in patients with neurodegenerative LSRDs. A multidisciplinary team reviewed over 750 evaluations in 274 patients. These patients were found to have neurological, sensory and somatic problems that considerably influence the results of neurobehavioural testing.
Conclusion: Treatment effects in patients with neurodegenerative LSRDs are best evaluated by repeated measures and longitudinal analysis of each domain of function.