Quantitative Clinical Characteristics of 53 Patients with MPS VII: A Cross-Sectional Analysis

Introduction: Mucopolysaccharidosis type VII (OMIM #253220) is a progressive neurometabolic disorder due to deficiency of the lysosomal enzyme β-glucuronidase (GUS). The natural history, especially survival as hard endpoint for clinical trials, has not been quantitated.

Patients and Methods: We quantitatively analyzed published cases with MPS VII (N = 53/88 with sufficient data). Main outcome measures were onset of disease and survival. The role of biomarkers such as GUS residual enzyme activity and levels of storage material assessed as urinary excretion of glycosaminoglycans (GAG) as potential predictors for the clinical outcome were investigated. The analysis was conducted according to STROBE criteria.

Results: The median survival of the postnatally diagnosed population was up to 360 months. Median age of onset of disease was the first day of life, and the median age at diagnosis was 11 months. Patients with residual GUS activity in fibroblasts above 1.4% or urinary GAG excretion below 602% of normal survived longer than patients with GUS enzyme activity below or GAG excretion above these thresholds.

Conclusion: MPS VII has its disease onset prenatally. In the absence of a prenatal diagnosis, most patients are clinically apparent at birth. Our data corroborate a phenotype–biomarker association in MPS VII. The survival data characterize the natural history with important implications for therapeutic studies.