Enzyme missing in refsum's disease is ?

Refsum's disease can manifest in infancy to early adulthood with the classic tetrad of (1) peripheral neuropathy, (2) retinitis pigmentosa, (3) cerebellar ataxia, and (4) elevated CSF protein concentration. Most affected individuals develop progressive distal sensory loss and weakness in the legs leading to foot drop by their 20 s . Subsequently, the proximal leg and arm muscles may become weak. Patients may also develop sensorineural hearing loss, cardiac conduction abnormalities, ichthyosis, and anosmia. Refsum's disease is genetically heterogeneous but autosomal recessive in nature. Classical Refsum's disease with childhood or early adult onset is caused by mutations in the gene that encodes for phytanoylCoA a-hydroxylase (PAHX). Less commonly, mutations in the gene encoding peroxin 7 receptor protein (PRX7) are responsible. These lead to the accumulation of phytanic acid in the central and peripheral nervous systems. Treatment is removal of phytanic precursors (phytols: fish oils, dairy products, and ruminant fats) from the diet Ref - Harrisons 20e p3211