Morquio disease: The role of cartilage canals in the pathogenesis of chondrogenic dwarfism

Summary 

Chondrogenic dwarfism in Morquio disease (mucopolysaccharidosis IV) has been suggested to be strongly linked to the abnormal lysosomal storage of cartilaginous extracellular matrix waste products within chondrocytes and fibroblasts. The specific genetic defects of enzymes of the keratan sulfate and chondroitin-6-sulfate metabolism have been detected at the molecular level and importantly contributed to the current knowledge on the phenotype of this rare metabolic disorder. However, the pathogenesis of this epiphyseal centered progressive skeletal disease does not seem to be fully explained by the dysfunction of the chondrocyte cytoplasm that presents with vacuolar changes in adult patients. I propose that the accumulation of extracellular matrix degradation product-laden macrophages within epiphyseal cartilage canals during the early postnatal period causes dysregulation in the synchronized process of the neoformation and resorption of the maturing radial growing epiphyses. Similarly, the resorption of pannus tissue following the microtraumatisation of weight-bearing joints and epiphysis-type bones becomes impacted. If the hypothesis is valid, the early pathogenesis in Morquio disease could be because of the inadequate regression of cartilage canals and impaired resorption and restitution of pannus tissue.