REFSUM-DISEASE IS CAUSED BY MUTATIONS IN THE PHYTANOYL-COA HYDROXYLASE GENE

Refsum disease is an autosomal-recessively inherited disorder characte rized clinically by a tetrad of abnormalities: retinitis pigmentosa, p eripheral neuropathy, cerebellar ataxia and elevated protein levels in the cerebrospinal fluid (CSF) without an increase in the number of ce lls in the CSF. All patients exhibit accumulation of an unusual branch ed-chain fatty acid, phytanic acid (3,7,11,15-tetramethylhexadecanoic acid), in blood and tissues. Biochemically, the disease is caused by t he deficiency of phytanoyl-CoA hydroxylase (PhyH), a peroxisomal prote in catalyzing the first step in the alpha-oxidation of phytanic acid. We have purified PhyH from rat-liver peroxisomes and determined the N- terminal amino-acid sequence, as well as an additional internal amino- acid sequence obtained after Lys-C digestion of the purified protein. A search of the EST database with these partial amino-acid sequences l ed to the identification of the full-length human cDNA sequence encodi ng PhyH: the open reading frame encodes a 41.2-kD protein of 338 amino acids, which contains a cleavable peroxisomal targeting signal type 2 (PTS2). Sequence analysis of PHYH fibroblast cDNA from five patients with Refsum disease revealed distinct mutations, including a one-nucle otide deletion, a 111-nucleotide deletion and a point mutation. This a nalysis confirms our finding that Refsum disease is caused by a defici ency of PhyH.