Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting motor neurones. In some familial forms of ALS, a mutation in the SOD1\text{SOD1}SOD1 gene leads to the production of a toxic, misfolded SOD1\text{SOD1}SOD1 protein. This toxic protein damages motor neurones, leading to demyelination (loss of the myelin sheath).
A recent clinical trial investigated a therapeutic drug, which consists of short, single-stranded DNA molecules designed to target the SOD1\text{SOD1}SOD1 gene product. The drug was administered via intrathecal injection (directly into the cerebrospinal fluid of the spinal canal).
Answer the following questions based on this information:
Explain how damage to the myelin sheath of motor neurones can lead to muscle paralysis.
Suggest and explain how this single-stranded DNA drug can cause a reduction in the concentration of the toxic SOD1\text{SOD1}SOD1 protein.
Suggest two reasons why the DNA drug is injected directly into the cerebrospinal fluid rather than taken orally as a pill.
