Refsum disease, usually called Adult Refsum disease to distinguish it from the unrelated form of the disease that affects newborns, is a genetic disorder where phytanic acid from the breakdown of fatty acids builds up in the body due to an inability of the body to properly process them. This results in damage to the central nervous system and peripheral nerves, resulting in disabilities to the brain and nerves. It usually presents after puberty.
Although plasmapheresis can be used in severe cases, the most common treatment is changes to the patient's diet to remove sources of phytanic acid. Most ruminant animals have high levels of the precursor to phytanic acid in their fat, as do some fish. The body also creates phytanic acid through the digestion of green vegetables in the gut.