Heterogeneity of Morquio disease.
Further clinical heterogeneity of Morquio disease, mucopolysaccharidosis IV (MPS IV), is delineated by the observation of a 30-year-old man with unusually mild clinical manifestations. He is 156 cm tall, has comparatively mild skeletal abnormalities and fine corneal deposits. Keratosulfaturia is absent. N-Acetylgalactosamine-6-sulfate (GalNAc-6-S) sulfatase (E.C. 3.1.6.-) was markedly reduced in his fibroblasts. The residual enzyme activity exhibited a pH profile comparable to that of patients with the "classical" form of the disorder. From our observation and a review of the literature it is concluded that Morquio disease can be divided in several subgroups: besides the severe ("classical") type A there exist an intermediate and a mild form that are also caused by a GalNAc-6-S sulfatase deficiency. A late-onset variant of Morquio disease, which is due to a deficiency of beta-galactosidase, has been classified as type B. In addition, patients with mild manifestation of the disease and normal activities in fibroblasts of GalNAc-6-S sulfatase and beta-galactosidase have been observed (type C). The genetic nature of the broad clinical variability of Morquio disease is incompletely understood: it is partially caused by different enzyme defects. Other factors thought to influence the clinical expression include the pH profile of the residual enzyme activity and an additional neuraminidase defect.
D000328:Adult; D002811:Chondroitinsulfatases / Q000172:deficiency; D005347:Fibroblasts / Q000201:enzymology; D014644:Genetic Variation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D009085:Mucopolysaccharidosis IV / Q000201:enzymology / Q000235:genetics*; D010641:Phenotype; D001616:beta-Galactosidase / Q000378:metabolism
D002811:Chondroitinsulfatases; D001616:beta-Galactosidase