Reduced fetal movements in late pregnancy with weakness and hypotonia at birth. Swallowing and sucking are impaired
The child lies with arms and legs abducted and externally rotated (hypotonic posture) Contractures, wasting and fasciculation gradually become evident
All motor milestones are delayed; 95% of all patients are dead by 18 months.
Type II - Kugelberg Welander disease (Late infantile or juvenile SMA)
Pathological features similar to Werdnig Hoffman disease.
Autosomal excessive (1:25 000 births) autosomal dominant (1:100 000 births)
It is slowly progressive with great variability even within the same family. Median age at death 12 years. Survival to adulthood occurs in the dominant form.
Type III (Adult onset SMA)
Caused hy three distinct genes - autosomal dominant, recessive and X linked recessive. Onset between 2nd and 5th decade with progressive limb girdle weakness. Distinction from progressive muscular atrophy form of ALS is difficult. A benign course supports the former.
Differentiation from HMSN types I and II (page 428) and scapuloperoneal dystrophy (page 453) is clinically difficult and separation may only be possible on histological and neurophysiological grounds.
Juvenile bulbar palsy (Kennedy syndrome)
X linked recessive disorder presenting in late childhood with drooling and dysarthria, progressing to aspiration pneumonia and respiratory failure characterised at Xql2 (androgen receptor gene). Limb involvement and pyramidal tract signs can occur. Few patients survive the second decade.
Management of spinal muscular atrophies
There is no specific treatment. Care is supportive. Genetic counselling is essential.
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