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Questions and Answers
What is the main role of the SMN2 gene in spinal muscular atrophy?
What is the main role of the SMN2 gene in spinal muscular atrophy?
- It partially compensates for the loss of SMN1 by producing SMN protein. (correct)
- It produces truncated SMN protein that is fully functional.
- It completely compensates for the loss of SMN1.
- It plays no significant role in the disease mechanism.
Why does a higher copy number of SMN2 generally lead to a milder disease phenotype in SMA?
Why does a higher copy number of SMN2 generally lead to a milder disease phenotype in SMA?
- More copies allow for greater functional SMN protein production. (correct)
- Higher SMN2 copy number leads to complete loss of symptoms.
- Increased SMN2 results in more stable motor neurons.
- It reduces the sensitivity of motor neurons to degeneration.
What distinguishes the SMN2 transcripts in patients with SMA?
What distinguishes the SMN2 transcripts in patients with SMA?
- All SMN2 transcripts include exon 7.
- They are expressed at lower levels compared to SMN1.
- A significant majority of SMN2 transcripts lack exon 7. (correct)
- They produce a larger amount of fully functional SMN protein.
What is the consequence of the homozygous loss of the SMN1 gene?
What is the consequence of the homozygous loss of the SMN1 gene?
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What variability is observed in SMA patients despite the relationship between SMN2 copy number and disease severity?
What variability is observed in SMA patients despite the relationship between SMN2 copy number and disease severity?
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Study Notes
Spinal Muscular Atrophy (SMA) and SMN Genes
- Homozygous loss of the SMN1 gene leads to spinal muscular atrophy (SMA).
- SMN1 deficiency is partially compensated by SMN2, which can produce the SMN protein; however, it is not sufficient for full compensation in motor neurons.
- SMN2 is transcribed at levels similar to SMN1 but primarily produces truncated transcripts lacking exon 7, leading to less stable and functional SMN protein.
Implications for Patients with SMA
- Patients with SMA lack functional SMN1 and rely on SMN2 for alpha motor neuron function and survival.
- The number of SMN2 gene copies correlates positively with the severity of SMA phenotype; more copies typically lead to milder symptoms.
- There is notable variability in SMA clinical presentations among patients with similar SMN2 copy numbers, indicating discordance between expected phenotype and actual presentation.
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