Phytanic acid is an unusual fatty acid which accumulates in patients with Refsum's disease. Phytanic acid is derived from phytol, a constituent of chlorophyll (Figure 18.20). Phytanic acid contains a methyl group on carbon number three and this prevents -oxidation from occurring. In this circumstance, -oxidation (Figure 18.20) would normally handle the problem, but patients with Refsum's disease cannot undergo -oxidation, so phytanic acid accumulates.

See also: -Oxidation