Evaluation of disease severity in mucopolysaccharidoses.

The mucopolysaccharidoses (MPS) are a group of lysosomal storage disorders characterized by a wide variation in symptoms and progression rates. Each of the MPS types is caused by a deficiency in one of the enzymes involved in the catabolic pathway of glycosaminoglycans. MPS are usually suspected on the basis of the concomitant presence of several typical features of the disease, such as short stature, coarse facial features, loss of hearing, bone deformities, joint stiffness, organomegaly, respiratory and cardiovascular complications, and, in some cases, developmental delay. Very reduced or absent enzyme activity is required to confirm an MPS diagnosis. In the past, treatment of MPS was limited to the management of individual symptoms of the diseases. Currently, specific therapies such as hematopoietic stem cell transplantation and enzyme replacement therapy have improved the outlook for many MPS patients. To monitor disease progression and the impact of therapy in these patients, there is need for a validated scoring system for evaluating disease severity in MPS. A scoring system should take into account all aspects of MPS, particularly quality of life and functioning of arms, hands and legs and related mobility, endurance, self care and social functioning. This paper discusses several of the available scoring systems for bone/skeletal disorders and their potential usefulness in patients with MPS.