What are FAOD?



Gene mutations impair enzyme activity1

Fatty acid oxidation disorders (FAOD) are a group of ultrarare genetic conditions in which an enzyme that ordinarily breaks down fat is either at a very low level or not functioning normally.

In healthy people, the body uses glucose (sugar) for energy. Once the body has used up all available glucose, it uses fatty acids as an energy source.

In people with FAOD, the enzyme responsible for breaking down fatty acids is either at a very low level or not functioning normally. Without being able to break down fatty acids, the body must find other energy sources, such as glucose. This causes the signs and symptoms of FAOD.

FAOD affect 1 in 4600 people in the United States2,3

Long-chain FAOD (LC-FAOD) are a specific group of FAOD. The most common types of LC-FAOD are

  • Very long–chain acyl-coenzyme A dehydrogenase (VLCAD) deficiency
  • Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD) deficiency
  • Trifunctional protein (TFP) deficiency
  • Carnitine palmitoyltransferase I and II (CPT I and II) deficiency
Life with FAOD: Tasia’s Story
Other kinds of FAOD4
  • Carnitine transport defect (primary carnitine deficiency)
  • Carnitine-acylcarnitine translocase (CACT) deficiency
  • 2,4 dienoyl-CoA reductase deficiency
  • Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency
  • Short-chain acyl-CoA dehydrogenase (SCAD) deficiency
  • 3-hydroxyacyl-CoA dehydrogenase (HADH) deficiency; also known as short-chain l-3-hydroxyacyl-CoA dehydrogenase (SCHAD) deficiency
  • Electron transfer flavoprotein (ETF) dehydrogenase deficiency; also known as glutaric aciduria II (GAII) or multiple acyl-CoA dehydrogenase (MAD) deficiency
  • 3-hydroxy-3methylglutaryl-CoA lyase (HMG) deficiency
  • Unclassified FAOD
CoA, coenzyme A.


FAOD are inherited in an autosomal recessive manner5

Autosomal recessive describes the way the genes are passed down. Everyone carries some recessive genes. If a person has only one copy of a recessive gene, they generally do not develop the disease associated with the recessive gene. However, if a person has two copies of an abnormal recessive gene, an autosomal recessive disease can develop.

These recessive genes are inherited. For a person to inherit FAOD, they must receive one abnormal gene from each parent.

If both parents are carriers of a gene with mutations, there is a 1 in 4 chance a person will develop FAOD.

Signs & symptoms4,6-8

Most people with FAOD will be diagnosed after newborn screening, however, some people with milder symptoms may not be diagnosed until later in childhood or even adulthood.

For many people with FAOD, getting sick, having an infection, and fasting can trigger symptoms. If symptoms are not treated properly, there is a risk of serious consequences. However, if precautions such as tailoring your diet and avoiding fasting are taken, people with FAOD can better manage their symptoms.

The most commonly seen signs and symptoms include:
  • Pain (muscle pains, cramps, weakness)
  • A breakdown of muscle fibers into the blood (rhabdomyolysis)
  • Low blood sugar (hypoglycemia)
  • Decreased muscle tone and weakness (hypotonia)
  • Heart muscle weakness (cardiomyopathy)

Other symptoms of FAOD

  • Foggy thinking
  • Nausea
  • Drowsiness
  • Fussiness
  • Lack of appetite
  • Loss of feeling in the arms and legs (because of rhabdomyolysis in older patients)
  • Blurry vision (because of hypoglycemia)

Diagnosing FAOD9-12

Most people are now diagnosed with FAOD after an abnormal newborn screening.
Starting in 1999, newborn screening gradually expanded by state to include testing for FAOD. People born before 1999 can be evaluated for suspected FAOD symptoms, and they may need to take a blood test.

Talk to your doctor if you suspect that you may have FAOD.
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References: 1. Fatty acid oxidation disorders. The Screening, Technology and Research in Genetics (STAR-G) Project. http://www.newbornscreening.info/Parents/fattyaciddisorders/Carnitine.html. Updated February 20, 2016. Accessed August 17, 2016. 2. Lindner M, Hoffmann GF, Matern D. Newborn screening for disorders of fatty-acid oxidation: experience and recommendations from an expert meeting. J Inherit Metab Dis. 2010;33(5):521-526. 3. Ultragenyx announces initiation of phase 2 study for patients with long-chain fatty acid oxidation disorders [press release]. Novato, CA: Ultragenyx Pharmaceutical Inc.; February 12, 2014. http://ir.ultragenyx.com/releasedetail.cfm?releaseid=824776. Accessed August 17, 2016. 4. List of FODs & symptoms. FOD Family Support Group. https://www.fodsupport.org/list.htm. Accessed August 17, 2016. 5. MCAD and other fatty acid oxidation disorders. Illinois Department of Public Health: Genetics and Newborn Screening. http://www.idph.state.il.us/HealthWellness/fs/mcad.htm. Accessed August 17, 2016. 6. Fatty acid oxidation disorders. March of Dimes. http://www.marchofdimes.org/complications/fatty-acid-oxidation-disorders.aspx. Updated January 2014. Accessed August 17, 2016. 7. Roe CR, Sweetman L, Roe DS, David F, Bruengraber H. Treatment of cardiomyopathy and rhabdomyolysis in long-chain fat oxidation disorders using an anaplerotic odd-chain triglyceride. J Clin Invest. 2002;110(2):259-269. doi:10.1172/JCI200215311. 8. Pitceathly RDS, Maritz C, Rahman S, et al. Fatty acid oxidation disorders in adults: a potentially treatable cause of muscle disease. http://www.kumc.edu/Documents/neurology/Pitceathly.pdf. 2009. 9. The National Newborn Screening and Genetics Resource Center. National Newborn Screening Report: 1999. Austin, TX: The National Newborn Screening and Genetics Resource Center; July 2002. 10. Waisbren SE, Landau Y, Wilson J, et al. Neuropsychological outcomes in fatty acid oxidation disorders: 85 cases detected by newborn screening. Dev Disabil Res Rev. 2013;17(3):260-268. doi:10.1002/ddrr.1119. 11. Frazier DM, Millington DS, McCandless SE, et al. The tandem mass spectrometry newborn screening experience in North Carolina: 1997-2005. J Inherit Metab Dis. 2006;29(1):76-85. 12. Zytkovicz TH, Fitzgerald EF, Marsden D, et al. Tandem mass spectrometric analysis for amino, organic, and fatty acid disorders in newborn dried blood spots: a two-year summary from the New England Newborn Screening Program. Clin Chem. 2001;47(11):1945-1955.