Makindo Medical Notes"One small step for man, one large step for Makindo" |
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Type | Other Name | 🧒 Age of Onset | 💪 Motor Function | 🫁 Respiratory Involvement | 📉 Prognosis |
---|---|---|---|---|---|
I | Werdnig–Hoffman Disease | Birth – 6 months | Never sit unaided, severe hypotonia, weak cry, tongue fasciculations | Severe, early respiratory failure | Life expectancy < 2 years (improved with modern therapy) |
II | Intermediate SMA | 6 – 18 months | Sit but never walk unaided, proximal weakness, tremor | Progressive, often scoliosis and restrictive lung disease | Survival into adolescence/adulthood possible |
III | Kugelberg–Welander Syndrome | 2 – 10 years | Walk initially but progressive difficulty; proximal weakness, frequent falls | Milder, but respiratory support may be needed later | Many survive into adulthood; slower progression |
IV | Adult-onset SMA | Adolescence to adulthood (>20 years) | Mild proximal weakness, gradual progression | Minimal or absent | Normal life expectancy, slow decline |
🧬 All SMA types share the same genetic cause (SMN1 mutations), but severity depends on SMN protein levels, often influenced by copy number of the SMN2 “backup gene.” Modern therapies (Nusinersen, Risdiplam, Zolgensma) have dramatically changed prognosis across all types.