Refsum disease (RD) is an autosomal recessive sensory motor neuropathy characterized by retinitis pigmentosa, peripheral neuropathy, anosmia, deafness, cerebellar ataxia and elevated protein concentrations in the cerebrospinal fluid in the absence of an increased number of cells. The age at which symptoms first present in RD can be variable although most cases present in adolescence. Because the patients are unable to metabolize phytanic acid derived from exogenous sources, highly raised plasma phytanic acid (PA) level in tissues and body fluids is the hallmark of RD. Mutant forms of phytanoyl-CoA 2-hydroxylase (PHYH) which plays a key role of phytanic acid alpha-oxidation in peroxisomes have been shown to be responsible for some, but not all, cases of Refsum's disease. Peroxisomal PHYH import occurs via PEX7 which is the peroxisomal matrix protein receptor. Though PEX7 has been identified another responsible gene, there still remain a small number of patients in whom no mutations in either of these two genes can be found.
