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[Alterations in functional proteins. Calpaine-3 deficiency]
A López de Munain1, A Urtasun, J J Poza
1Servicio de Neurología, Hospital Ntra, Sra. de Aránzazu, San Sebastián, Guipúzcoa.
Introduction:
Muscular dystrophies due to calpain deficiency are the first example of a muscular dystrophy due to the mutation of a gene codifying for a non-structural enzymatic protein of unknown function and substrate.
Development:
More than 70 mutations have been described in the gene structure, localized to chromosome 15. Although the time course and topography is fairly homogeneous, correlation between the different mutations and the phenotype has still to be analyzed. The age of onset of symptoms is usually between 8 and 14, with no difference between the sexes. There is a slow but uniformly progressive course starting in the pelvis and extending to the shoulder and the distal musculature. Almost all patients are confined to a wheelchair twenty years after onset of the disease. There is no facial, oculomotor or bulbar involvement and gemellar pseudohypertrophy is rare. However, a winged scapula and marked lumbar hyperlordosis is universal. No cardiac or cognitive changes have been observed. Muscle CT shows a pattern of atrophy, mainly of the posterior and medial muscle compartments and of the posterosuperficial group of the legs, which varies depending on the time the disorder has been present. This condition is the commonest etiological group of the dystrophy syndromes, especially of those of late infancy or juvenile onset, in the open populations studied to date. Muscle biopsy, stained by all methods available, is essential to rule out other types of progressive dystrophies secondary to deficiencies of structural proteins.
Insights
Calpain deficiency causes muscular dystrophy, a genetic disorder affecting muscle structure and function. This condition, characterized by progressive muscle weakness, typically begins in childhood and leads to significant mobility impairment.
Area of Science:
- Neuromuscular disorders
- Enzymatic protein deficiencies
- Genetic basis of muscular dystrophy
Context:
- Calpain deficiency represents the first identified muscular dystrophy linked to mutations in a gene encoding a non-structural enzymatic protein.
- Over 70 mutations identified in the calpain gene on chromosome 15.
- Characterized by a progressive, homogeneous clinical course affecting pelvic and shoulder musculature.
Purpose:
- To analyze the correlation between specific calpain gene mutations and the resulting phenotype.
- To detail the clinical presentation, progression, and diagnostic features of calpain deficiency muscular dystrophy.
- To establish calpain deficiency as a common etiological group within dystrophy syndromes.
Summary:
- Onset typically between ages 8-14, with slow, progressive muscle weakness starting in the pelvis and spreading distally.
- Universal findings include winged scapula and lumbar hyperlordosis; no facial, bulbar, cardiac, or cognitive involvement observed.
- Muscle CT reveals atrophy patterns, primarily in posterior compartments; muscle biopsy is crucial for differential diagnosis.
Impact:
- Provides a comprehensive understanding of calpain deficiency muscular dystrophy, aiding in diagnosis and management.
- Highlights the significance of non-structural enzymatic proteins in muscle health.
- Contributes to the classification and etiological understanding of muscular dystrophy syndromes.