| Discussion: |
Background: Morquio syndrome is a member of a group of inherited metabolic disorders collectively termed mucopolysaccharidoses (MPSs). The MPSs are caused by a deficiency of lysosomal enzymes required for the degradation of mucopolysaccharides or glycosaminoglycans (GAGs). Currently, 11 distinct single lysosomal enzyme deficiencies are known to cause 7 recognized phenotypes of MPS. All the MPSs are inherited in an autosomal recessive fashion except Hunter syndrome (MPS type II), which is X-linked.
In the early 1930s, Husler coined the term dysostosis multiplex to describe the constellation of skeletal findings specific to patients with MPS and other lysosomal storage disorders. These included a large skull with a J-shaped sella, anterior hypoplasia of the thoracic and lumbar vertebral bodies, hypoplasia of the pelvis with small femoral heads and coxa valga, oar-shaped ribs (narrow at the vertebrae and widening anteriorly), diaphyseal and metaphyseal expansion of long bones with cortical thinning, and tapering of the proximal phalanges. However, this family of diseases was not described as the MPSs until 1952, when Brante isolated the stored mucopolysaccharides in these patients.
Patients with Morquio syndrome usually can be clinically distinguished from patients with other MPSs because they do not have coarse facial features or mental retardation and they have additional skeletal manifestations derived from a unique spondyloepiphyseal dysplasia and ligamentous laxity. These skeletal manifestations include odontoid hypoplasia, a striking short trunk dwarfism, and genu valgus. Compared to other patients with MPS, those with Morquio syndrome tend to have greater spine involvement with scoliosis, kyphosis, and severe gibbus, as well as platyspondylia, rib flaring, pectus carinatum, and ligamentous laxity. Odontoid hypoplasia is the most critical skeletal feature to recognize in any patient with Morquio syndrome.