Biochemistry · Topic
Lysosomal storage diseases !
When a lysosomal enzyme is missing, the molecule it should break down stays inside, the lysosome swells and the cell eventually fails.
Updated 2026-11-01
Key facts
- More than 70 single-gene diseases; together about 1 in 5,000 live births.
- Mechanism: loss of an acid hydrolase, its activator protein, mannose 6-phosphate tagging, or a carrier that exports products from the lysosome.
- Groups: sphingolipidoses (Gaucher, Tay–Sachs, Niemann–Pick, Fabry, Krabbe, metachromatic leukodystrophy), mucopolysaccharidoses (Hurler, Hunter), glycogenosis II (Pompe), mucolipidoses (I-cell disease).
- The organ hit depends on where the substrate turns over most: gangliosides in neurons, glucosylceramide in macrophages, GAGs in connective tissue.
- Nearly all are autosomal recessive; Fabry and Hunter are X-linked.
In detail
- 1. Material reaches the lysosome by endocytosis, phagocytosis or autophagy and should leave as monomers (sugars, amino acids, fatty acids).
- 2. If one enzyme fails, its intermediate substrate builds up and lysosomes grow until they distort the cell (Gaucher cells, foam cells).
- 3. Storage disturbs autophagy, membrane traffic and calcium, and triggers inflammation; the cell dies or works poorly.
- 4. Residual enzyme activity sets the severity: no activity, infantile form; some activity, juvenile or adult forms.
- 5. Diagnosis: enzyme activity in leukocytes or dried blood spots, substrates in urine (GAGs, oligosaccharides) or blood, and genetic testing.
- 6. Treatments: enzyme replacement (the recombinant enzyme enters through the mannose 6-phosphate or mannose receptor), substrate reduction, pharmacological chaperones, haematopoietic stem cell transplant, and gene therapy under study.
- 7. Infused enzyme does not cross the blood–brain barrier well: replacement improves organs and bone but helps the brain little.
- Also called
- Lysosomal storage disorders
Clinical notes
- Clinical clues: hepatosplenomegaly, developmental regression, coarse facial features, dysostosis multiplex, cherry-red spot or corneal clouding.
- Foam cells or Gaucher cells in bone marrow support the diagnosis, which is confirmed by enzyme and gene testing.
- Families are offered genetic counselling, and prenatal diagnosis when the variant is known.
Pathways
Related conditions
- Gaucher disease
- Tay–Sachs disease
- Niemann–Pick disease
- Fabry disease
- Krabbe disease (globoid cell leukodystrophy)
- Metachromatic leukodystrophy
- Hurler syndrome (mucopolysaccharidosis type I)
- Hunter syndrome (mucopolysaccharidosis type II)
- I-cell disease (mucolipidosis II)
- Pompe disease (glycogen storage disease type II)
- Sandhoff disease
- Sanfilippo syndrome (mucopolysaccharidosis type III)
- Morquio syndrome (mucopolysaccharidosis type IV)
Related
- Sphingolipids and sphingolipidoses
- Glycosaminoglycans (mucopolysaccharides)
- Mannose 6-phosphate tagging (sending enzymes to the lysosome)
- Cell organelles and their metabolism
- Glucocerebrosidase (acid β-glucosidase)
- Hexosaminidase A (β-hexosaminidase A)
- α-Galactosidase A
- Acid sphingomyelinase
- α-L-Iduronidase
Test yourself
Think of the answer, then tap the question to see it.
Why does enzyme replacement not improve brain damage in most lysosomal diseases?
The recombinant enzyme is a large protein that does not cross the blood–brain barrier.
Which classic lysosomal diseases are X-linked?
Fabry and Hunter (MPS II); the others are autosomal recessive.
What decides whether a lysosomal disease is infantile or adult-onset?
Residual enzyme activity: less activity means earlier and more severe disease.
How does replacement enzyme reach the cell's lysosomes?
By endocytosis through mannose 6-phosphate or mannose receptors on the cell surface.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Lysosome Vesicle Biogenesis (Reactome, 2026); Glycosphingolipid metabolism (Reactome, 2026); Glycosaminoglycan metabolism (Reactome, 2026); Gaucher disease: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.