Diagnostic journey and impact of enzyme replacement therapy for mucopolysaccharidosis IVA: a sibling control study

Mucopolysaccharidosis (MPS) IVA, also known as Morquio A syndrome, is a rare autosomal recessive lysosomal storage disorder caused by a deficiency in the enzyme N-acetylgalactosamine-6-sulfatase. Early recognition, diagnosis, and treatment of this progressive, multisystem disease by enzyme replacement therapy (ERT) can lead to improved outcomes and reduced mortality.

This report documents the diagnostic journey and treatment with ERT of three siblings with MPS IVA. Clinical outcome measures included growth, endurance, imaging, cardiac, respiratory, ophthalmology, and laboratory evaluations.

Three siblings, diagnosed at 14.7, 10.1, and 3.2 years of age, demonstrated clinical improvement with weekly infusions of 2.0 mg/kg elosulfase alfa (Vimizim^®, BioMarin Pharmaceutical, Novato, CA, USA). Patient 1 (oldest sibling) and Patient 2 (middle sibling) experienced a diagnostic delay of 8 years 7 months and 4 years after symptom onset, respectively. All three patients demonstrated improvements in growth, 6-min walk distance, joint range of motion, and respiratory function after 30 months of ERT. The treatment was well tolerated without any adverse events.

This case series highlights the importance of early recognition of the clinical and imaging findings that are initially subtle in MPS IVA. Early treatment with ERT is necessary to slow irreversible disease progression and improve patient outcomes. The oldest sibling experienced improvements in mobility despite severe symptoms resulting from a late diagnosis. When evaluating patients with skeletal anomalies, imaging multiple body regions is recommended. When findings such as anterior beaking of vertebrae or bilateral femoral head dysplasia are present, MPS IVA should be included in the differential diagnosis. Newborn screening must be considered for early detection, accurate diagnosis, and initiation of treatment to reduce morbidity.