Spinal muscle atrophy

1. What is the inheritance pattern of SMA?
2. What is the onset and course of the different types of SMA?
3. What is the presentation of SMA type I?
4. What is the presentation of SMA type II?
5. What is the presentation of SMA type III?
6. What is seen on labs and muscle biopsy?

Answers:
1. Autosomal recessive (sometimes dominant with type III).
2. Type I has onset 3-6 months and death by 2-3 years (resp failure). Type II has onset at 2-12 months, wheelchair by 2-3 years, and death by age 10. Type III has onset 2-15 years, WC by 30 years, normal life expectancy.
3. Floppy baby, absent MSR, weak cry, tongue fasciculation, EOMI, facial muscles least affected, never sits independently.
4. Floppy baby, kyphoscoliosis, independent sitting, assistance for standing and walking.
5. Symmetric weakness, lower limb more than upper, Gower's sign, calf pseudohypertrophy, dysphagia, dysarthria, tongue fascic, normal intelligence, independent standing/walking.
6. Blood shows incr CPK. Muscle biopsy shows hyper/atrophic fibers.