Mucolipidosis II and III: different residual activity of beta‐galactosidase in cultured fibroblasts*

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Abstract
A biochemical difference is found between the mucolipidoses II and III which may be correlated with their clinical phenotypes. In homogenates of mass‐cultured I‐cells from patients with MLII (I‐cell disease), the residual specific activity of beta‐galactosidase is between 3 and 5 times lower than that in the I‐cells from patients with MLIII (pseudo‐polydystrophy). This difference is confirmed in several covershlip culture experiments where conditions of inoculation, propagation, harvest and enzyme assays are rigidly controlled. MLIII cells also hydrolyse the natural substrates asialofetuin‐(H)3‐galactoside and GM1‐(H)2‐galactoside more easily. This observation offers support to the hypothesis that beta‐galactosidase may play a role in the physiopathology of these mucolipidoses.