[I-cell disease and pseudo-Hurler polydystrophy]

Area of Science:

• Biochemistry
• Genetics
• Cell Biology

Context:

• Lysosomal storage diseases (LSDs) encompass a group of inherited metabolic disorders.
• I-cell disease (Mucolipidosis II, ML II) and pseudo-Hurler poly-dystrophy (ML-III) are specific LSDs characterized by impaired lysosomal enzyme targeting.
• These diseases result from a defect in the UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-1-phosphotransferase (GlcNAc-1-phosphotransferase) enzyme, crucial for proper enzyme phosphorylation and lysosomal localization.

Purpose:

• To investigate the underlying molecular mechanisms of I-cell disease (ML II) and pseudo-Hurler poly-dystrophy (ML-III).
• To analyze the consequences of defective lysosomal enzyme phosphorylation and localization in affected patients.
• To report on the natural history and clinical observations of ML II and ML-III cases.

Summary:

• ML II and ML-III are lysosomal storage diseases caused by deficient GlcNAc-1-phosphotransferase activity, leading to aberrant phosphorylation and extracellular secretion of lysosomal enzymes instead of lysosomal delivery.
• Despite the general deficiency in enzyme targeting, liver cells from ML II patients exhibit normal intracellular lysosomal enzyme content, suggesting tissue-specific variations or compensatory mechanisms.
• The study reports on the clinical course of 21 diagnosed ML II cases and 5 prenatally identified ML II cases, providing insights into the natural history of this rare disorder.

Impact:

• This research enhances the understanding of the pathophysiology of ML II and ML-III, particularly the role of GlcNAc-1-phosphotransferase in lysosomal trafficking.
• The findings contribute to the diagnostic and potentially therapeutic strategies for these debilitating genetic disorders.
• The comparative prevalence data highlights geographical variations in ML II and ML-III, with ML II being more common in Japan than in Western countries.