Damage to the myelin sheath of neurones can cause muscular paralysis (lines 2–4).

Explain how.

Sometimes Guillain–Barré syndrome causes heart rate irregularities (lines 4–5).

Suggest and explain why.

The first successful drug trial to reduce concentrations of huntingtin in the brain used single-stranded DNA molecules (lines 13–14).

Suggest and explain how this drug could cause a reduction in the concentration of the protein huntingtin.

Scientists from the first successful drug trial to reduce concentrations of huntingtin (lines 9–11) reported that the drug is not a cure for Huntington's disease.

Suggest two reasons why the drug should not be considered a cure. Do not include repeats of the drug trial in your answer.

1

2

Suggest two reasons why people had the drug injected into the cerebrospinal fluid (lines 12–13) rather than taking a pill containing the drug.

1

2

Suggest and explain one way epigenetics may affect the age when symptoms of Huntington's disease start.