A very rare, clinically variable, multisystemic metabolic disease, characterized by anosmia, early-onset retinitis pigmentosa and possible neurological manifestations, including neuropathy, and cerebellar ataxia, deafness, ichthyosis, skeletal abnormalities, and cardiac arrhythmia. It is characterized biochemically by accumulation of phytanic acid in plasma and tissues. The disease is MONDO_0009958 (adult Refsum disease). Also known as: HMSN 4, HMSN type IV, HSMN IV, Refsum Disease, Refsum disease, Refsum disease, adult, 1, Refsum disease, classic, Refsum's disease.