Mucopolysaccharidosis type IVA (MPS IVA; Morquio A syndrome) is a rare autosomal recessive lysosomal storage disorder characterized by the accumulation of keratan sulfate (KS) and chondroitin-6-sulfate (C6S) resulting from the deficient activity of N-acetyl-galactosamine-6-sulfatase (GALNS). The most common characteristics of patients with MPS IVA are progressive skeletal dysplasia, short stature and motor dysfunction with normal intelligence. The experience with ERT in severely affected, non-ambulatory patients has been reported only in a few studies. Here, we describes clinical course for the 2-year efficacy and safety of ERT with elosulfase alfa in a severely affected, non-ambulatory patients with Morquio A syndrome. Efficacy measures were urine keratin sulfate, echocardiography, pulmonary function test, and FIM. In addition, we tried to find the efficacy of ERT in these patients on the individual basis. The efficacy results can be highly variable due to challenges in test execution because of severe skeletal and joint abnormalities, small sample sizes, and clinical heterogeneity among patients. Some patients indicate improvements not captured by the general assessments. To measure impact of ERT objectively in very disabled Morquio A patients is considerably challenging, and to examine results on an individual basis is needed (e.g., increased energy, functional ability).