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Lysosomal storage diseases
This is a large group of disorders due to defects in lysosomal function.
A group of IMD caused by deficiency in lysosomal enzymes needed to break down glycosaminoglycans (long chain carbohydrate molecules for-merly called mucopolysaccharides). Affects bone, cartilage, tendons, eyes, skin, and connective tissue, leading to accumulation of glycosaminoglycans and progressive cellular and tissue damage.
Clinical features are not apparent at birth, but progress with time as storage of glycosaminoglycans impacts on tissues and organs. Typical fea-tures include:
• Neuropathy: peripheral/spinal.
• Neurodevelopmental delay; hearing loss (conductive/sensory); hydrocephalus.
• Visual loss: corneal clouding/glaucoma/retinal degeneration.
• Coarsening of facial features.
• Short stature/skeletal deformities; joint stiffness.
• Valvular heart disease.
Clinically the sphingolipidoses show variable severity. They cause progres-sive peripheral and CNS disease (psychomotor retardation, myoclonus, weakness, and spasticity).
Variants of Gaucher and Niemann–Pick disease that do not affect the nervous system are termed non-neuronopathic.
• Fabry’s disease
• GM1 gangliosidoses
• GM2 gangliosidoses
• Tay–Sachs disease
• Sandhoff disease
• Gaucher’s disease
• Krabbe disease
• Metachromatic leucodystrophy
• Niemann–Pick disease
X-linked recessive. Due to a deficiency of alpha galactosidase A, result-ing in the accumulation of globotriaosylceramide within blood vessels and other tissues. Clinical features become evident in early childhood and increase in severity with age—anhidrosis; fatigue; skin lesions (angiokera-tomas: tiny, painless papules); and burning pain of the extremities. Renal failure, heart disease, and stroke increase with age. Other symptoms include tinnitus, vertigo, nausea, and diarrhoea.
AR. This is the most common lysosomal storage disorder. It is due to deficient activity of beta-glucocerebrosidase and leads to intracellular accumulation of glucosylceramide (glucosylcerebroside) within cells of mononuclear phagocyte origin (producing characteristic ‘Gaucher cells’).
Gaucher disease is categorized phenotypically into 3 main subtypes:
• Type I Gaucher disease: most common form of Gaucher disease—lacks p CNS involvement. Wide spectrum of severity, ranging from affected infants to asymptomatic adults. Usually presents in childhood with hepatosplenomegaly, pancytopenia, and bone marrow infiltration. Severe orthopaedic complications, including vertebral compression, avascular necrosis of the femoral head, and pathological fractures of long bones.
• Type II acute neuronopathic: acute neuronopathic form of the disorder starts in infancy, and death is often by 2yrs of age. Patients are usually normal at birth, but develop hepatosplenomegaly, developmental regression, and growth arrest within a few months of age.
• Type III subacute neuronopathic: subacute form similar to type II Gaucher disease, but has later age of onset and slower progression.
A heterogeneous group of disorders of glycoprotein storage. A spectrum of phenotypes include neurological deterioration, growth retardation, visceromegaly, and seizures. Also coarse facial features, angiokeratoma corporis diffusum, spasticity, and delayed development.
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