What is the refsum disease?(prevalence,history)

An uncommon disease: Refsum disease is a disease that causes loss of vision and smell, poor balance, and weakness or numbness of the hands and feet. Due to a genetic abnormality, people lack the enzyme in that breaks down a type of fat found in certain foods. Treatment entails avoiding foods with phytanic acid. Symptoms appear anywhere from childhood to the 50s. The prevalence is unknown, but thought to be small.