This family is made up of several eukaryotic phytanoyl-CoA dioxygenase (PhyH) proteins, ectoine hydroxylases and a number of bacterial deoxygenases. PhyH is a peroxisomal enzyme catalysing the first step of phytanic acid alpha-oxidation. PhyH deficiency causes Refsum's disease (RD) which is an inherited neurological syndrome biochemically characterized by the accumulation of phytanic acid in plasma and tissues.