Medicine & USMLE

Werdnig-Hoffman Disease (SMA Type 1)

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Spinal Lesions
  1. UMN vs. LMN Lesions
  2. Werdnig-Hoffman Disease (SMA Type 1)
  3. Amyotrophic Lateral Sclerosis (ALS)
  4. Tabes Dorsalis
  5. Cauda Equina Syndrome
  6. Syringomyelia
  7. Brown-Sequard Syndrome

Werdnig-Hoffman Disease (SMA Type 1)

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Summary

Werdnig-Hoffman Disease, otherwise known as Spinal Muscular Atrophy Type 1, is an autosomal recessive inherited condition that causes degeneration of the anterior horn of the spinal cord. This is caused by a mutation to the gene SMN1 on chromosome 5q, which results in defective snRNP. This impairs the development of the lower motor neurons in infants. Some signs of this LMN damage include hypotonia and flaccid paralysis, muscle atrophy, and tongue fasciculations.

Key Points

  • (Infantile) Spinal Muscular Atrophy (SMA)
    • SMA Type 1 is also called Werdnig-Hoffman Disease
    • Pathology
      • Congenital degeneration of anterior horns
        • Cell bodies of lower motor neurons of corticospinal tract
      • SMN1 mutation on chromosome 5q
        • Defective snRNP (small nuclear ribonucleoproteins) assembly, causing defective spliceosomes
      • Autosomal recessive inheritance
    • Presentation
      • Usually seen in infants
      • LMN signs
        • Marked hypotonia (flaccid paralysis)
          • “floppy baby” appearance
        • Muscle atrophy
        • Tongue fasciculations
        • Infants may have frog-like posture