Progressive mental regression in siblings with Morquio disease type B (mucopolysaccharidosis IV B).
A brother and sister with clinical and radiological features of Morquio disease, but with atypical mental regression, are described. Leucocyte and fibroblast beta-galactosidase activity was deficient in the siblings, while N-acetylgalactosamine 6-sulphate sulphatase and neuraminidase were normal. Study of the residual fibroblast beta-galactosidase activity towards 4-methylumbelliferyl and p-nitrophenyl beta-D-galactosides indicated that the mutation resembles that in typical Morquio B disease (increased Km and similar pH maximum) rather than that in GM1-gangliosidosis. The patients have therefore been classified as having Morquio B disease with atypical mental regression rather than GM1-gangliosidosis variants with particularly severe bony abnormalities. The mutation was, however, distinct from that in Morquio B disease since residual activity towards the alternative artificial substrate 4-methylumbelliferyl-beta-D-fucoside was increased. The patients represent further examples of the heterogeneity that can result from mutation at the beta-galactosidase locus.
D001848:Bone Diseases, Developmental / Q000000981:diagnostic imaging / Q000201:enzymology / Q000235:genetics; D002648:Child; D002908:Chronic Disease; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008607:Intellectual Disability / Q000201:enzymology / Q000235:genetics*; D008297:Male; D009085:Mucopolysaccharidosis IV / Q000201:enzymology / Q000235:genetics*; D011859:Radiography; D001616:beta-Galactosidase / Q000378:metabolism
D001616:beta-Galactosidase