The table below shows some details of three genetic conditions that affect humans.
| Disease | Cause | Rate of cases | Effect |
|---|---|---|---|
| Cystic fibrosis | a recessive allele | 1 in 2,500 people | The mutation prevents a cell membrane protein from transporting chloride ions, causing thick mucus to build up. |
| Familial hypercholesterolaemia | a dominant allele | 1 in 250 people | The mutation prevents the liver from removing low-density lipoproteins (LDL) from the blood. |
| Charcot-Marie-Tooth (CMT) disease | a dominant allele | 15 in 100,000 people | The mutation produces a faulty protein that damages the myelin sheath of peripheral motor neurones. |
There are 56 million people in a country. Calculate the number of cases of CMT disease expected in this country.
Explain why CMT disease can cause difficulty in walking, using the information about its effect from the table.