Inclusion-Cell (I-Cell) Disease (Mucolipidosis Type II) Workup

Updated: Aug 08, 2017
  • Author: Karl S Roth, MD; Chief Editor: Luis O Rohena, MD, FAAP, FACMG  more...
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Workup

Laboratory Studies

Biochemical diagnosis can be made in the following ways:

  • N -acetylglucosaminyl-1-phosphotransferase activity can be measured in WBCs or in cultured fibroblasts.
  • Various lysosomal enzyme activities can be measured in serum and in cultured fibroblasts. The activities of beta-hexosaminidase, iduronate sulfatase, and arylsulfatase A are deficient in cultured fibroblasts, but their serum levels are 10-20 times the reference range. Assays for lysosomal enzymes in leukocytes are not reliable because of mannose-6-phosphate–independent targeting pathways.
  • Dried blood spot screening methodology has been reported. [11]
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Imaging Studies

Radiography

The characteristic bone changes are similar to those observed in the mucopolysaccharidoses. [8] There may be fractures, bone rarification, and other findings leading to confusion with rickets. [12]

The classic finding is dysostosis multiplex, with a cloaking appearance of the long tubular bones, anterior beaking and wedging of the vertebral bodies, widening of the ribs, proximal pointing of the metacarpals, and bullet-shaped phalanges.

Brain imaging

Brain imaging is not necessary to diagnose I-cell disease, although it is often performed during evaluation of developmental delay.

MRI and CT scan findings can be variable and nonspecific and may not aid in the diagnosis. Reported MRI and CT scan findings include completely normal scans with normal myelination, cerebral atrophy, and nonspecific white matter changes.

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Histologic Findings

A unique finding in I-cell disease is the presence of numerous intracytoplasmic inclusions in cells of mesenchymal origin that are observed on electron microscopy. These inclusions are membrane-bound vacuoles filled with fibrillogranular material. The contents of these vacuoles have not been well characterized; however, they appear to contain various lipids, mucopolysaccharides, and oligosaccharides.

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