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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed January 2010

What is the official name of the PHYH gene?

The official name of this gene is “phytanoyl-CoA 2-hydroxylase.”

PHYH is the gene's official symbol. The PHYH gene is also known by other names, listed below.

What is the normal function of the PHYH gene?

The PHYH gene provides instructions for making an enzyme called phytanoyl-CoA hydroxylase. This enzyme is critical for the normal function of cell structures called peroxisomes. These sac-like compartments contain enzymes needed to break down many different substances, including fatty acids and certain toxic compounds.

One substance that is broken down in peroxisomes is phytanic acid, a type of fatty acid obtained from the diet (particularly from beef and dairy products). Phytanoyl-CoA hydroxylase is responsible for one of the first steps in breaking down phytanic acid as part of a process known as alpha-oxidation. In subsequent steps, additional enzymes in peroxisomes and other parts of the cell further process this compound into smaller molecules that the body can use for energy.

Researchers suspect that phytanoyl-CoA hydroxylase may have other functions in addition to its role in breaking down phytanic acid. For example, this enzyme appears to help determine the number of peroxisomes within cells and is involved in regulating their activity.

How are changes in the PHYH gene related to health conditions?

Refsum disease - caused by mutations in the PHYH gene

Mutations in the PHYH gene have been found to cause more than 90 percent of all cases of Refsum disease. About 30 mutations in this gene have been identified. These mutations alter the structure or production of phytanoyl-CoA hydroxylase, which reduces the enzyme's activity. A shortage of this enzyme disrupts the breakdown of phytanic acid in peroxisomes. As a result, phytanic acid and related compounds build up in the body's tissues. The accumulation of phytanic acid is toxic to cells, although it is unclear how an excess of this substance affects vision and smell and causes the other specific features of Refsum disease.

Where is the PHYH gene located?

Cytogenetic Location: 10p13

Molecular Location on chromosome 10: base pairs 13,277,796 to 13,300,138

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The PHYH gene is located on the short (p) arm of chromosome 10 at position 13.

The PHYH gene is located on the short (p) arm of chromosome 10 at position 13.

More precisely, the PHYH gene is located from base pair 13,277,796 to base pair 13,300,138 on chromosome 10.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about PHYH?

You and your healthcare professional may find the following resources about PHYH helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the PHYH gene or gene products?

  • LN1
  • LNAP1
  • PAHX
  • PHYH1
  • phytanic acid oxidase
  • phytanoil-CoA alpha hydroxylase
  • phytanoyl-CoA 2 oxoglutarate dioxygenase
  • phytanoyl-CoA alpha-hydroxylase
  • phytanoyl-CoA dioxygenase, peroxisomal

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding PHYH?

acids ; breakdown ; cell ; CoA ; compound ; enzyme ; fatty acids ; gene ; oxidase ; oxidation ; peroxisomes ; toxic

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Gene Review: Refsum Disease (
  • Jansen GA, Hogenhout EM, Ferdinandusse S, Waterham HR, Ofman R, Jakobs C, Skjeldal OH, Wanders RJ. Human phytanoyl-CoA hydroxylase: resolution of the gene structure and the molecular basis of Refsum's disease. Hum Mol Genet. 2000 May 1;9(8):1195-200. (
  • Jansen GA, Ofman R, Ferdinandusse S, Ijlst L, Muijsers AO, Skjeldal OH, Stokke O, Jakobs C, Besley GT, Wraith JE, Wanders RJ. Refsum disease is caused by mutations in the phytanoyl-CoA hydroxylase gene. Nat Genet. 1997 Oct;17(2):190-3. (
  • Jansen GA, Wanders RJ, Watkins PA, Mihalik SJ. Phytanoyl-coenzyme A hydroxylase deficiency -- the enzyme defect in Refsum's disease. N Engl J Med. 1997 Jul 10;337(2):133-4. (
  • Jansen GA, Waterham HR, Wanders RJ. Molecular basis of Refsum disease: sequence variations in phytanoyl-CoA hydroxylase (PHYH) and the PTS2 receptor (PEX7). Hum Mutat. 2004 Mar;23(3):209-18. Review. (
  • McDonough MA, Kavanagh KL, Butler D, Searls T, Oppermann U, Schofield CJ. Structure of human phytanoyl-CoA 2-hydroxylase identifies molecular mechanisms of Refsum disease. J Biol Chem. 2005 Dec 9;280(49):41101-10. Epub 2005 Sep 25. (
  • Mihalik SJ, Morrell JC, Kim D, Sacksteder KA, Watkins PA, Gould SJ. Identification of PAHX, a Refsum disease gene. Nat Genet. 1997 Oct;17(2):185-9. (
  • Mukherji M, Chien W, Kershaw NJ, Clifton IJ, Schofield CJ, Wierzbicki AS, Lloyd MD. Structure-function analysis of phytanoyl-CoA 2-hydroxylase mutations causing Refsum's disease. Hum Mol Genet. 2001 Sep 1;10(18):1971-82. (
  • NCBI Gene (
  • van den Brink DM, Wanders RJ. Phytanic acid: production from phytol, its breakdown and role in human disease. Cell Mol Life Sci. 2006 Aug;63(15):1752-65. Review. (
  • Wanders RJ, Komen JC. Peroxisomes, Refsum's disease and the alpha- and omega-oxidation of phytanic acid. Biochem Soc Trans. 2007 Nov;35(Pt 5):865-9. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: January 2010
Published: February 1, 2016