Potassium-aggravated myotonia is a rare genetic disorder that affects skeletal muscle.

Myotonia causes muscle stiffness, often painful, that worsens after exercise and may be aggravated by eating potassium-rich foods such as bananas and potatoes.

The SCN4A gene provides instructions for making a protein that is critical for the normal function of skeletal muscle cells.

The influx of extra sodium ions triggers prolonged muscle contractions, which are the hallmark of myotonia.

[citation needed] Potassium-aggravated myotonia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.