Lysosomal Storage Diseases

LSDs Overview - Enzyme Trouble Tales

• LSDs Defined: Inherited metabolic disorders; specific enzyme deficiency → lysosomal dysfunction → toxic accumulation of undegraded substrates.
• Common Features: Progressive, multi-systemic involvement.
  • Organomegaly (esp. hepatosplenomegaly).
  • Neurological regression/decline.
  • Skeletal dysplasia (e.g., dysostosis multiplex).
  • Coarse facial features (in some types).
• Inheritance Pattern: Mostly Autosomal Recessive (AR).
  • 📌 Key Exceptions (X-Linked Recessive): Fabry disease, Hunter syndrome (MPS II).
• Basic Pathophysiology: Deficient lysosomal enzyme → Accumulation of its specific substrate within lysosomes → Cellular engorgement & dysfunction → Progressive organ damage.

⭐ Most Lysosomal Storage Diseases are Autosomal Recessive. Remember the two major X-Linked Recessive exceptions: Fabry disease and Hunter syndrome (MPS II).

Sphingolipidoses - Lipid Mayhem Mess

• Gaucher Disease: Glucocerebrosidase ↓; Glucocerebroside ↑. Hepatosplenomegaly, pancytopenia, bone crises, pain. 📌 Gaucher cells (crumpled tissue paper macrophages), Erlenmeyer flask deformity.
• Niemann-Pick Disease (A/B): Sphingomyelinase ↓; Sphingomyelin ↑. Type A: Severe neurodegeneration, cherry-red spot, hepatosplenomegaly, early death. Type B: Visceral, less neuro. 📌 Foam cells.
• Tay-Sachs Disease: Hexosaminidase A ↓; GM2 Ganglioside ↑. Progressive neurodegeneration, developmental delay, cherry-red spot (NO hepatosplenomegaly). 📌 Onion-skin lysosomes.
• Fabry Disease (X-linked): α-Galactosidase A ↓; Globotriaosylceramide (Gb3) ↑. Episodic peripheral neuropathy (acroparesthesias), angiokeratomas, hypohidrosis, renal failure, cardiac issues.
• Krabbe Disease (Globoid Cell Leukodystrophy): Galactocerebrosidase ↓; Galactocerebroside/Psychosine ↑. Rapid neurodegeneration, irritability, optic atrophy, peripheral neuropathy. 📌 Globoid cells.
• Metachromatic Leukodystrophy (MLD): Arylsulfatase A ↓; Sulfatides ↑. Progressive demyelination → motor (ataxia) & cognitive decline, peripheral neuropathy.

⭐ Tay-Sachs and Niemann-Pick Type A both present with a cherry-red spot, but Tay-Sachs lacks hepatosplenomegaly.

Mucopolysaccharidoses - Sugar Stash Snags

• General: Defective Glycosaminoglycan (GAG) breakdown. Chronic, progressive.
  • Features: Coarse facies, dysostosis multiplex, organomegaly, joint stiffness. Corneal clouding (exceptions: Hunter, Sanfilippo).
• Hurler Syndrome (MPS I-H):
  • Deficiency: $\alpha$-L-Iduronidase. AR.
  • Key: Most severe. Corneal clouding, HSM, neurodegeneration.
• Hunter Syndrome (MPS II):
  • Deficiency: Iduronate-2-Sulfatase. X-Linked Recessive.
  • Key: NO corneal clouding.
  • 📌 Mnemonic: "Hunters see clearly (no corneal clouding) & aim for X (X-linked)".
• Others:
  • Sanfilippo (MPS III): Neurodegeneration.
  • Morquio (MPS IV): Severe skeletal issues, normal intellect, corneal clouding.

⭐ Hunter Syndrome (MPS II) is the only X-linked recessive MPS; others are autosomal recessive.

LSD Diagnosis & Management - Spot & Support Strategy

• Diagnosis:
  • Clinical suspicion guides.
  • Enzyme assays (leukocytes, fibroblasts, plasma specific to LSD).
  • Genetic testing (confirmatory, carrier detection, prenatal).
  • Urine GAG analysis for MPS.
• Management: Largely supportive & symptomatic.
  • ERT: For Gaucher, Fabry, Pompe, MPS I, II, IVA, VI. Regular IV.

    ⭐ ERT is available for Gaucher, Fabry, Pompe, and several MPS types, but is costly with limited CNS reach.

  • SRT: Oral drugs. Miglustat (Gaucher type 1, NPC), Eliglustat (Gaucher type 1).
  • HSCT: For some CNS forms (e.g., early Hurler, Krabbe) if done early.
  • Future: Gene therapy, chaperone therapy.

High‑Yield Points - ⚡ Biggest Takeaways

• LSDs: Caused by deficient lysosomal enzymes leading to substrate accumulation.
• Inheritance: Mostly autosomal recessive, except Fabry & Hunter (X-linked).
• Gaucher: Glucocerebrosidase deficiency; crumpled tissue paper cells; hepatosplenomegaly.
• Tay-Sachs: Hexosaminidase A deficiency; cherry-red spot; NO hepatosplenomegaly.
• Niemann-Pick: Sphingomyelinase deficiency; cherry-red spot; hepatosplenomegaly; foam cells.
• Fabry: α-Galactosidase A deficiency; X-linked; angiokeratomas, peripheral neuropathy.
• Hunter (MPS II): Iduronate-2-sulfatase deficiency; X-linked; aggressive behavior, NO corneal clouding.