Mucopolysaccharidosis type IVA (Morquio A disease): clinical review and current treatment

Mucopolysaccharidosis IVA (MPS IVA), also known as Morquio A, is a rare, autosomal recessive disorder caused by a deficiency of the lysosomal enzyme N-acetylgalatosamine-6-sulfate-sulfatase (GALNS), which catalyzes a step in the catabolism of glycosaminoglycans (GAGs), keratan sulfate (KS) and chondroitin-6-sulfate (C6S). It leads to accumulation of the KS and C6S, mainly in bone and cornea, causing a systemic skeletal chondrodysplasia. MPS IVA has a variable age of onset and variable rate of progression. Common presenting features include elevation of urinary and blood KS, marked short stature, hypoplasia of the odontoid process, pectus carinatum, kyphoscoliosis, genu valgum, laxity of joints and corneal clouding; however there is no central nervous system impairment. Generally, MPS IVA patients with a severe form do not survive beyond the third decade of life whereas those patients with an attenuated form may survive over 70 years. There has been no effective therapy for MPS IVA, and care has been palliative. Enzyme replacement therapy (ERT) and hematopoietic stem cell therapy (HSCT) have emerged as a treatment for mucopolysaccharidoses disorders, including Morquio A disease. This review provides an overview of the clinical manifestations, diagnosis and symptomatic management of patients with MPS IVA and describes potential perspectives of ERT and HSCT. The issue of treating very young patients is also discussed.