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

Peroxisomal acyl-CoA oxidase deficiency

Reviewed April 2014

What is peroxisomal acyl-CoA oxidase deficiency?

Peroxisomal acyl-CoA oxidase deficiency is a disorder that causes deterioration of nervous system functions (neurodegeneration) beginning in infancy. Newborns with peroxisomal acyl-CoA oxidase deficiency have weak muscle tone (hypotonia) and seizures. They may have unusual facial features, including widely spaced eyes (hypertelorism), a low nasal bridge, and low-set ears. Extra fingers or toes (polydactyly) or an enlarged liver (hepatomegaly) also occur in some affected individuals.

Most babies with peroxisomal acyl-CoA oxidase deficiency learn to walk and begin speaking, but they experience a gradual loss of these skills (developmental regression), usually beginning between the ages of 1 and 3. As the condition gets worse, affected children develop exaggerated reflexes (hyperreflexia), increased muscle tone (hypertonia), more severe and recurrent seizures (epilepsy), and loss of vision and hearing. Most children with peroxisomal acyl-CoA oxidase deficiency do not survive past early childhood.

How common is peroxisomal acyl-CoA oxidase deficiency?

Peroxisomal acyl-CoA oxidase deficiency is a rare disorder. Its prevalence is unknown. Only a few dozen cases have been described in the medical literature.

What genes are related to peroxisomal acyl-CoA oxidase deficiency?

Peroxisomal acyl-CoA oxidase deficiency is caused by mutations in the ACOX1 gene, which provides instructions for making an enzyme called peroxisomal straight-chain acyl-CoA oxidase. This enzyme is found in sac-like cell structures (organelles) called peroxisomes, which contain a variety of enzymes that break down many different substances. The peroxisomal straight-chain acyl-CoA oxidase enzyme plays a role in the breakdown of certain fat molecules called very long-chain fatty acids (VLCFAs). Specifically, it is involved in the first step of a process called the peroxisomal fatty acid beta-oxidation pathway. This process shortens the VLCFA molecules by two carbon atoms at a time until the VLCFAs are converted to a molecule called acetyl-CoA, which is transported out of the peroxisomes for reuse by the cell.

ACOX1 gene mutations prevent the peroxisomal straight-chain acyl-CoA oxidase enzyme from breaking down VLCFAs efficiently. As a result, these fatty acids accumulate in the body. It is unclear exactly how VLCFA accumulation leads to the specific features of peroxisomal acyl-CoA oxidase deficiency. However, researchers suggest that the abnormal fatty acid accumulation triggers inflammation in the nervous system that leads to the breakdown of myelin, which is the covering that protects nerves and promotes the efficient transmission of nerve impulses. Destruction of myelin leads to a loss of myelin-containing tissue (white matter) in the brain and spinal cord; loss of white matter is described as leukodystrophy. Leukodystrophy is likely involved in the development of the neurological abnormalities that occur in peroxisomal acyl-CoA oxidase deficiency.

Related Gene(s)

Changes in this gene are associated with peroxisomal acyl-CoA oxidase deficiency.

  • ACOX1

How do people inherit peroxisomal acyl-CoA oxidase deficiency?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Where can I find information about diagnosis or management of peroxisomal acyl-CoA oxidase deficiency?

These resources address the diagnosis or management of peroxisomal acyl-CoA oxidase deficiency and may include treatment providers.

  • Gene Review: Leukodystrophy Overview (
  • Genetic Testing Registry: Pseudoneonatal adrenoleukodystrophy (

You might also find information on the diagnosis or management of peroxisomal acyl-CoA oxidase deficiency in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about peroxisomal acyl-CoA oxidase deficiency?

You may find the following resources about peroxisomal acyl-CoA oxidase deficiency helpful. These materials are written for the general public.

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

What other names do people use for peroxisomal acyl-CoA oxidase deficiency?

  • pseudoadrenoleukodystrophy
  • pseudo-NALD
  • pseudoneonatal adrenoleukodystrophy
  • straight-chain acyl-CoA oxidase deficiency

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about peroxisomal acyl-CoA oxidase deficiency?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding peroxisomal acyl-CoA oxidase deficiency?

acids ; autosomal ; autosomal recessive ; breakdown ; cell ; CoA ; deficiency ; demyelination ; enzyme ; epilepsy ; fatty acids ; gene ; hypertelorism ; hypotonia ; inflammation ; inherited ; leukodystrophy ; molecule ; muscle tone ; nervous system ; neurological ; oxidase ; oxidation ; peroxisomes ; polydactyly ; prevalence ; recessive ; regression ; tissue ; white matter

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


  • Carrozzo R, Bellini C, Lucioli S, Deodato F, Cassandrini D, Cassanello M, Caruso U, Rizzo C, Rizza T, Napolitano ML, Wanders RJ, Jakobs C, Bruno C, Santorelli FM, Dionisi-Vici C, Bonioli E. Peroxisomal acyl-CoA-oxidase deficiency: two new cases. Am J Med Genet A. 2008 Jul 1;146A(13):1676-81. doi: 10.1002/ajmg.a.32298. (
  • Clayton PT. Clinical consequences of defects in peroxisomal beta-oxidation. Biochem Soc Trans. 2001 May;29(Pt 2):298-305. Review. (
  • El Hajj HI, Vluggens A, Andreoletti P, Ragot K, Mandard S, Kersten S, Waterham HR, Lizard G, Wanders RJ, Reddy JK, Cherkaoui-Malki M. The inflammatory response in acyl-CoA oxidase 1 deficiency (pseudoneonatal adrenoleukodystrophy). Endocrinology. 2012 Jun;153(6):2568-75. doi: 10.1210/en.2012-1137. Epub 2012 Apr 16. (
  • Ferdinandusse S, Denis S, Hogenhout EM, Koster J, van Roermund CW, IJlst L, Moser AB, Wanders RJ, Waterham HR. Clinical, biochemical, and mutational spectrum of peroxisomal acyl-coenzyme A oxidase deficiency. Hum Mutat. 2007 Sep;28(9):904-12. (
  • Kurian MA, Ryan S, Besley GT, Wanders RJ, King MD. Straight-chain acyl-CoA oxidase deficiency presenting with dysmorphia, neurodevelopmental autistic-type regression and a selective pattern of leukodystrophy. J Inherit Metab Dis. 2004;27(1):105-8. (
  • Su HM, Moser AB, Moser HW, Watkins PA. Peroxisomal straight-chain Acyl-CoA oxidase and D-bifunctional protein are essential for the retroconversion step in docosahexaenoic acid synthesis. J Biol Chem. 2001 Oct 12;276(41):38115-20. Epub 2001 Aug 10. (
  • Suzuki Y, Iai M, Kamei A, Tanabe Y, Chida S, Yamaguchi S, Zhang Z, Takemoto Y, Shimozawa N, Kondo N. Peroxisomal acyl CoA oxidase deficiency. J Pediatr. 2002 Jan;140(1):128-30. (


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: April 2014
Published: February 1, 2016