AMACR and Refsum disease: Patients with Zellweger syndrome (Ferdinandusse et al., 2001) have low AMACR activity and patients with AMACR mutations (S52P and L107P) accumulate toxic levels of branched-chain fatty acids in the blood, causing neuropathy similar to Refsum disease (Ferdinandusse et al., 2000a; Wilson et al., 2011; Herzog et al., 2017).