Spinal muscular atrophy (NMD) Flashcards
Describe spinal muscular atrophy
- Genetic condition causing progressive weakning of the muscles and mobility problems
- Due to degeneration of alpha motor neurones in the spinal cord and brain stem
What is the incidence of spinal muscular atrophy?
1/6,000 to 1/10,000
What is the prevalence of SMA?
1 in 100,000
Describe the aetiology of SMA (3)
- Autosomal recessive mutations in a single gene locus on the short arm of chromosome 5
- Causing a homozygous deletion
- Homozygous mutation of the SMN1 gene, testing generally shows absence of exon 7
Describe the inheritance patterns of SMA (2)
- Usually as an autosomal recessive trait
2. Two genes are required, one from each parent
What is the classification of SMA? (5)
- Type 1 SMA (young babies)
- Type 2 SMA (older babies and toddlers)
- Type 3 SMA (children and young adults)
- Type 4 SMA (adults)
- Other types
Describe the symptoms of Type 1 SMA (3)
- Very weak, floppy arms and legs (hypotonia)
- Problems eating, moving, breathing and swallowing
- Unable to raise head or sit without support
Describe the symptoms of SMA 2 (5)
- May sit up without support but cannot stand or walk
- Weak arms or legs
- Tremors in hands/fingers
- Joint problems eg. socliosis
- Weak breathing muscles and difficulty coughing
Describe the onset of Type 1 SMA
Show symptoms within first 6 months
Describe the prognosis of Type 1 SMA
Usually die within few years, usually due to respiratory problems
Describe the onset of Type 2 SMA
Symptoms show between 7-18 months
Describe the prognosis of Type 2 SMA (2)
- Usually less severe than Type 1
2. Can shorten life expectancy but most survive to adulthood
Describe the onset of Type 3 SMA (2)
- Symptoms after 18 months
2. Very variable - sometimes not until late childhood
Describe the symptoms of Type 3 SMA (4)
- Able to stand and walk without support but difficulty getting up from sitting position
- Balance problems, difficulty running and climbing stairs
- Tremors in fingers
- Walking gradually gets harder and may lose ability to walk
Describe the prognosis of Type 3 SMA (2)
- Doesn’t usually affect life expectancy
2. May lose ability to walk
Describe the onset of Type 4 SMA
Usually begins early adulthood
Describe the symptoms of Type 4 SMA (3)
- Weakness in hands and feet
- Difficulty walking
- Shaking and switching muscles
Describe the prognosis of Type 4 SMA
Gradually progresses over time but doesn’t usually affect breathing, swallowing or life expectency
Give 3 other types of SMA
- Spinal muscular atrophy with respiratory distress (SMARD)
- Kennedy’s disease or spinobulbar muscular atrophy
- Distal spinal muscular atrophy (DSMA)
Describe spinal muscular atrophy with respiratory distress (SMARD)
Type of SMA usually diagnosed during first year and can cause serious breathing problems
Describe Kennedy’s disease/spinobulbar muscular atrophy (4)
- Rare type of SMA
- Only affects men
- Starts in middle age
- Doesn’t usually impact life expectancy
Describe distal spinal muscular atrophy (DSMA)
- Type of SMA that mainly affects hands, feet, lower arms and lower legs
Summarise the diagnosis of SMA
- Family history
- Electromyography
- Blood tests
- Amniocentesis
- Muscle biopsy
What does electromyography find in SMA?
Conduction is normal but affected muscles (which are often clinically unaffected) are denervated
