Overview

• Multiminicore Disease (MmD): A clinically and genetically heterogeneous congenital myopathy characterized by multiple small cores in muscle fibers on biopsy.
• Main Forms:
  1. Rigid Spine Muscular Dystrophy Type 1 (RSMD1):
     • Caused by recessive SEPN1 mutations.

     Clinical Features

     1. 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.
        • Prognosis:
          • Most remain independently ambulant despite respiratory challenges.

     2. 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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     Information

     Published:04 January 2025 Last Updated:04 January 2025