Diagnosis of I-cell disease.

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I-cell disease (mucolipidosis II) is a rare lysosomal storage disease, with its primary defect the deficiency of an enzyme responsible for lysosomal enzyme processing, resulting in multiple lysosomal enzyme insufficiency. Diagnosis of I-cell disease usually can be made by the specific patterns of enzyme distribution: deficient intracellular, but excessive extracellular, enzymes. A six month old female infant was found to have bilateral congenital dislocation of hips, developmental delay, coarsening of facial appearance and dysostosis multiplex. In view of the very early onset of disease, I-cell disease was suspected. Lysosomal enzyme tests (including alpha-mannosidase, alpha-fucosidase, beta-glucuronidase and beta-galactosidase) were performed on the leukocytes, skin fibroblasts, plasma and media from fibroblast cultures. All activities of the four enzymes were low in both leukocytes and fibroblasts, but were 10- to 70-fold higher than normal in plasma, and high in culture media. Both the clinical and laboratory findings here were consistent with a diagnosis of I-cell disease.