Lysosomal storage disease

Editor-In-Chief: Prab R Tumpati, MD
Obesity, Sleep & Internal medicine
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Lysosomal storage disease
Synonyms	N/A
Pronounce	N/A
Specialty	N/A
Symptoms	Organomegaly, developmental delay, neurological symptoms
Complications	Organ failure, neurological deterioration
Onset	Varies by specific disease
Duration	Lifelong
Types	N/A
Causes	Genetic mutation
Risks	Family history
Diagnosis	Genetic testing, enzyme assay
Differential diagnosis	Mitochondrial disease, peroxisomal disorder
Prevention	N/A
Treatment	Enzyme replacement therapy, substrate reduction therapy
Medication	N/A
Prognosis	Varies by specific disease
Frequency	Rare
Deaths	N/A

Lysosomal Storage Diseases (LSDs) are a group of approximately 50 inherited metabolic disorders that result from defects in lysosomal function. Lysosomes are membrane-bound organelles found in nearly all animal cells. They are responsible for breaking down cellular waste products and recycling cellular components, a process crucial for cell maintenance and function. In LSDs, an enzyme deficiency within the lysosome leads to an accumulation of undigested or partially digested macromolecules, which in turn causes cell dysfunction and the clinical manifestations of the disease.

Etiology and Pathogenesis

LSDs are caused by mutations in genes that encode lysosomal enzymes, membrane proteins, or other proteins involved in lysosomal function. These genetic defects lead to a deficiency or malfunction of specific enzymes, preventing the normal breakdown of substrates within the lysosome. As a result, substrates accumulate within the lysosome, disrupting cellular function and leading to the clinical features of the disease.

Classification

LSDs can be classified based on the nature of the primary stored material. Major classes include:

• Mucopolysaccharidoses (MPS) - characterized by the accumulation of glycosaminoglycans (GAGs).
• Sphingolipidoses - caused by the accumulation of sphingolipids.
• Glycoproteinoses - involve the accumulation of glycoproteins.
• Mucolipidoses - characterized by the accumulation of both glycoproteins and lipids.

Clinical Manifestations

The clinical manifestations of LSDs are diverse and depend on the specific disease. Common symptoms may include organomegaly (enlargement of the liver, spleen), skeletal abnormalities, neurological deficits, and developmental delay. The severity and onset of symptoms vary widely, even within the same disorder.

Diagnosis

Diagnosis of LSDs typically involves a combination of clinical evaluation, biochemical tests to measure enzyme activity in blood, urine, or tissue samples, and molecular genetic testing to identify specific genetic mutations.

Treatment

Treatment options for LSDs are limited and vary depending on the specific disease. Approaches may include:

• Enzyme Replacement Therapy (ERT) - involves the intravenous administration of recombinant enzyme to replace the deficient enzyme.
• Substrate Reduction Therapy (SRT) - aims to reduce the synthesis of the substrate that accumulates due to the enzyme deficiency.
• Hematopoietic Stem Cell Transplantation (HSCT) - has been used in some LSDs to provide a source of normal enzyme-producing cells.
• Supportive care to manage symptoms and improve quality of life.

Prognosis

The prognosis for individuals with LSDs varies widely depending on the specific disease, age of onset, and severity of symptoms. Early diagnosis and intervention can improve outcomes for some individuals.

Research Directions

Research in LSDs is focused on developing new treatments, including gene therapy, which aims to correct the underlying genetic defect, and chaperone therapy, which aims to enhance the function of the residual enzyme.

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