Human phytanoyl-CoA hydroxylase: resolution of the gene structure and the molecular basis of Refsum's disease

Abstract

Refsum's disease (RD) is an inherited neurological syndrome biochemically characterized by the accumulation of phytanic acid in plasma and tissues. Patients with RD are unable to degrade phytanic acid due to a deficient activity of phytanoyl-CoA hydroxyl-ase (PhyH), a peroxisomal enzyme catalysing the first step of phytanic acid alpha-oxidation. To enable mutation analysis of RD at the genome level, we have elucidated the genomic organization of the PHYH gene. The gene is approximately 21 kb and contains nine exons and eight introns. Mutation analysis of PHYH cDNA from 22 patients with RD revealed 14 different missense mutations, a 3 bp insertion, and a 1 bp deletion, which were all confirmed at the genome level. A 111 bp deletion identified in the PHYH cDNA of several patients with RD was due to either one of two different mutations in the same splice acceptor site, which result in skipping of exon 3. Six mutations, including a large in-frame deletion and five missense mutations, were expressed in the yeast Saccharomyces cerevisiae to study their effect on PhyH activity. The results showed that all these mutations lead to an enzymatically inactive PhyH protein.

Biochemistry and genetics of inherited disorders of peroxisomal fatty acid metabolism

“…These can be grouped into several classes: mutations that affect the targeting (P 29 S), the active sites for binding Fe 2+ and/or oxoglutarate (D 177 G, R 275 Q, R 275 W), the overall conformation (W 193 F, I 199 F, F 257 S), or those that result in truncations, frame shift, and deletions ( 80,81 ). In case the mutation affects the 2-oxoglutarate binding site (R 275 Q, R 275 W), the activity can be restored by the use of alternative 2-oxoacids (chemical cosubstrate rescue), at least in vitro ( 82 ).…”

Identification of PEX7 as the Second Gene Involved in Refsum Disease

“…Solid and open arrows indicate the position of the unprocessed and mature forms, respectively. Immunoblot analyses were performed, as described, for peroxisomal thiolase (Heikoop et al 1990), ADHAPS (de Vet et al 1997), and PhyH with affinity-purified antibodies (Jansen et al 2000).…”

Studies on the specificity of unprocessed and mature forms of phytanoyl-CoA 2-hydroxylase and mutation of the iron binding ligands

“…Defects in the ␣ -oxidation pathway result in neurological syndromes in humans, including adult Refsum's disease (ARD) (2,5,6). Approximately 45% of cases of ARD in the United Kingdom are associated with defects in phytanoylcoenzyme A 2-hydroxylase (PAHX) (7)(8)(9), some other cases are associated with defects in the Pex7 transporter protein responsible for the importation of PAHX into peroxisomes (10), and some remain unidentified.…”