Overview
- Multiminicore Disease (MmD): A clinically and genetically heterogeneous congenital myopathy characterized by multiple small cores in muscle fibers on biopsy.
- Main Forms:
- Rigid Spine Muscular Dystrophy Type 1 (RSMD1):
- Caused by recessive SEPN1 mutations.
Clinical Features
-
Rigid Spine Syndrome Phenotype (RSMD1):
- Cause: Recessive mutations in SEPN1 (Selenoprotein N).
- Onset: First year of life.
- Symptoms:
- Hypotonia and weakness:
- Predominantly axial weakness.
- Neck flexors most affected → poor/absent head control in infancy.
- Joint hyperextensibility.
- Delayed motor development.
- Facial weakness: Common.
- Extraocular muscles spared.
- Kyphoscoliosis and spinal rigidity:
- Progressive, especially during adolescence.
- Often associated with respiratory insufficiency.
- Respiratory involvement:
- Progressive insufficiency typically develops in late adolescence or early adulthood.
- Intellectual performance: Normal.
- Hypotonia and weakness:
- Prognosis:
- Most remain independently ambulant despite respiratory challenges.
-
RYR1-Related Multiminicore Myopathy:
- Cause: Recessive mutations in RYR1 (ryanodine receptor).
- Symptoms:
- Similar distribution of weakness and wasting as RSMD1.
- Ophthalmoplegia:
- Extraocular muscle involvement (e.g., limited abduction, upward gaze).
- Bulbar involvement:
- May be pronounced (e.g., swallowing difficulties).
- Respiratory insufficiency:
- Milder compared to RSMD1.
- Prevalence:
- More common than SEPN1-associated RSMD1.
Pathological Features
- Allelic to Central Core Disease (CCD).
- Often associated with ophthalmoplegia.
Genetics
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- Rigid Spine Muscular Dystrophy Type 1 (RSMD1):