Скачать или смотреть 11. Mucolipidoses | Glycoprotein Degradation & Clinical Aspects, Lysosomal Storage Disorders | USMLE

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Mucolipidoses | Glycoprotein Degradation & Clinical Aspects | Lysosomal Storage Disorders | MBBS | USMLE Step 1

👋 Hey future doctors and biochem learners! Did you know that defects in glycoprotein degradation pathways can lead to a rare group of lysosomal storage diseases called Mucolipidoses? 🧬⚠️

These disorders combine features of mucopolysaccharidoses (MPS) and sphingolipidoses, hence the name mucolipidoses, and present with developmental delay, organomegaly, skeletal abnormalities, and coarse facial features.

This lecture explains the degradation of glycoproteins (GP), the biochemical basis of mucolipidoses, and their clinical aspects, making it highly relevant for MBBS, NEET PG, FMGE, and USMLE Step 1. 📚

🌟 Glycoprotein Degradation Pathway

Glycoproteins are degraded in lysosomes by sequential removal of sugars using specific exoglycosidases (e.g., neuraminidase, β-galactosidase, α-mannosidase, fucosidase).

Defects in these enzymes → accumulation of partially degraded glycoproteins → lysosomal storage.

Results in cell and tissue dysfunction.

🌟 Types of Mucolipidoses

1️⃣ Mucolipidosis II (I-cell disease)

Defect in N-acetylglucosamine phosphotransferase → failure to add mannose-6-phosphate to lysosomal enzymes.

Enzymes secreted extracellularly instead of targeted to lysosomes.

Clinical 🩺: Severe developmental delay, coarse facial features, skeletal abnormalities, gingival hyperplasia, early death.

2️⃣ Mucolipidosis III (Pseudo-Hurler Polydystrophy)

Partial defect in same enzyme.

Clinical 🩺: Milder course, joint stiffness, skeletal deformities, survival into adulthood.

3️⃣ Other Rare Glycoprotein Degradation Disorders

Fucosidosis: defect in α-fucosidase.

Mannosidosis: defect in α-mannosidase.

Sialidosis: defect in neuraminidase.

Clinical 🩺: Coarse facial features, organomegaly, developmental delay.

🩺 Clinical Aspects

Common Features:
• Coarse facies.
• Skeletal deformities (dysostosis multiplex).
• Hepatosplenomegaly.
• Neurological decline.

Laboratory Findings:
• Enzyme assays (specific lysosomal hydrolase activity).
• Elevated lysosomal enzymes in plasma (I-cell disease hallmark).
• Genetic testing confirms diagnosis.

🎯 Exam Integration

I-cell disease = failure of mannose-6-phosphate tagging → lysosomal enzymes secreted outside cell.

Mucolipidoses resemble mucopolysaccharidoses but involve glycoproteins.

Case clue: Infant with coarse facies + skeletal deformities + high plasma lysosomal enzymes → think I-cell disease.

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❓Should we make a separate comparative lecture: MPS vs Mucolipidoses vs Sphingolipidoses, so you can revise all lysosomal storage disorders at a glance? Drop your request in the comments below! 😊

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