P020: Baseline characteristics and medical history of participants enrolled in the MPS VII Disease Monitoring Program (DMP)

Introduction: MPS VII is an ultra-rare, autosomal recessive, debilitating, progressive lysosomal storage disease caused by beta-glucuronidase (GUSB) enzyme deficiency.Methods: The DMP is an ongoing, multicenter, observational study collecting standardized real-world data from participants with MPS VII.Results: Thirty-seven participants have enrolled in the DMP; 7 have withdrawn.Mean (SD) age at enrollment was 13.4 (10.8) years with a range of 1.5-50.2years.Variants in GUSB have been collected in 33 participants and are largely missense variants, and GUSB enzyme deficiencies in 30 participants show a wide range of enzyme levels.Thirty-one participants (84%) had received vestronidase alfa (VA).Mean (SD) duration of VA was 5.85 (2.79) years with few reported adverse events.Urine glycosaminoglycan levels show dermatan sulfate was consistently reduced >60% since pre-treatment baseline levels.Reductions have been maintained through at least month 60. 27 participants (73%) were born at term, 6 (16%) were preterm, and 4 (11%) were unknown.Seventeen patients (46%) had a history of non-immune hydrops fetalis or similar neonatal presentations.Intellectual disability was reported for 26 patients (70%): 6 profound, 6 severe, 4 moderate, 7 mild, and 3 unknown severity.At DMP baseline, delays in developmental milestones were observed: 14% were unable to sit independently, 14% were unable to walk independently, 22% were unable to eat independently, and 43% were unable to speak full sentences.Patients with NIHF included 4/17 (24%) born preterm.Twelve (71%) had intellectual disability, 11 (65%) reported as severe or profound.Of the 6 babies born preterm, 4 (67%) had NIHF.Five (83%) had intellectual disability, 4 (67%) reported as severe or profound.Conclusion: At baseline, patients with more severe presentations, including NIHF and preterm birth, have more severe intellectual disability.The MPS VII DMP provides a unique longitudinal evaluation of disease progression to better understand long-term clinical outcomes.