Abstract
Morquio B disease (MBD) is an autosomal recessive GLB1-gene-related lysosomal storage disease, presenting with a peculiar type of dysostosis multiplex which is also observed in GALNS-related Morquio A disease. MBD may present as pure skeletal phenotype (pure MBD) or in combination with the neuronopathic manifestations seen in type 2 (juvenile) or type 3 (late onset) GM1 gangliosidosis (MBD plus). The main skeletal features are progressive growth impairment, kyphoscoliosis, coxa/genua valga, joint laxity, platyspondyly and odontoid hypoplasia. The main neuronopathic features are dystonia, ataxia, and intellectual/developmental/speech delay. Spinal cord compression occurs as a complication of spinal dysostosis. Chronic pain is reported, along with mobility issues and challenges with daily living and self-care activities, as the most common health concern. The most commonly reported orthopedic surgeries are hip and knee replacements. Keratan sulphate-derived oligosaccharides are characteristic biomarkers. Residual β-galactosidase activities measured against synthetic substrates do not correlate with the phenotype. W273 L and T500A are the most frequently observed GLB1 variants in MBD, W273L being invariably associated with pure MBD. Cytokines play a role in joint destruction and pain, providing a promising treatment target. In the future, patients may benefit from small molecule therapies, and gene and enzyme replacement therapies, which are currently being developed for GM1 gangliosidosis.
Highlights
Morquio B disease (MBD), called Mucopolysaccharidosis IVB (OMIM # 253010), is a rare lysosomal storage disorder with a reported prevalence of 1:250,000–1,000,000 live births [1]
GLB1 mutations are typically associated with a progressive neuronopathic condition spanning from infantile to juvenile and late onset GM1 gangliosidosis
While genetically MBD is an allelic variant of GM1 gangliosidosis, clinically it is a mild phenocopy of GALNS-related Morquio A disease, which is characterized by the same type of spondyloepiphyseal dysplasia involving trabecular parts of long bones and the spine
Summary
Morquio B disease (MBD), called Mucopolysaccharidosis IVB (OMIM # 253010), is a rare lysosomal storage disorder with a reported prevalence of 1:250,000–1,000,000 live births [1]. MBD is caused by distinct mutations in the GLB1 gene. GLB1 mutations are typically associated with a progressive neuronopathic condition spanning from infantile to juvenile and late onset GM1 gangliosidosis. MBD (OMIM # 230500) presents with a unique dysostosis multiplex, causing a peculiar type of spondylo-epiphyseal dysplasia with or without additional neuronopathic manifestations. While genetically MBD is an allelic variant of GM1 gangliosidosis, clinically it is a mild phenocopy of GALNS-related Morquio A disease, which is characterized by the same type of spondyloepiphyseal dysplasia involving trabecular parts of long bones and the spine. W273L, T500A, R210H, G438E, Y333C, G438E, T384S, Y333H (not invariably associated with MBD)
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