Spinal (Bulbospinal) Muscular Atrophy

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Spinal (Bulbospinal) Muscular Atrophy (SMA)

Group of inherited neurodegenerative disorders that begin in infants or children (most are autosomal recessive – defect(s) on chromosome 5). Characterised by progressive symmetric weakness and wasting of muscle – from degeneration and loss of lower motor neurons. Affects 1/10 000 newborn. Most due to mutation on chromosome 5.

Main types:
Type 1 SMA (Werdnig-Hoffman Disease):
• almost always fatal before age of 18 –27 months due to respiratory failure; 1/20 000 live births; M=F; autosomal recessive
• hypotonic at birth – ‘floppy infant’; lower limbs in ‘frog leg’ position; poor feeding; weak cry

Type 2 SMA (intermediate form):
• symptomatic by 6-12 months; delay of motor milestones are most common presentation; hypotonic and weakness of muscles; absent deep tendon reflexes; tongue fasciculations; can usually sit independently, but unable to stand or walk; contractures develop if weakness untreated
• most survive intro adolescence or early adulthood; usually fatal from respiratory complications
• life expectancy can be increased with spinal fusion to prevent kyphoscoliosis and with good respiratory management

Type 3 SMA (Juvenile spinal muscular atrophy/Kugelberg-Welander Disease):
• onset around 2-3yrs, often later; survive until 20-30’s; variable progression rates – similar to Type 1, but slower progress; autosomal recessive
• onset is with progressive proximal muscle weakness; progression is slow; scoliosis, kyphosis, weakness and wasting in legs, equinovarus feet (mimics limb-girdle muscular dystrophy)
• management – prevention of contractures and scoliosis; respiratory care

Type 4 SMA:
usually autosomal dominant (but is variable); adult onset; slow progression

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