Fatty Oxidation Disorders
Robert Tomaino, Medical Writer
Fatty acid oxidation disorders (FODs) are a group of rare inborn errors of metabolism marked by the abnormal accumulation of fatty acids in the body. These disorders occur because of problems in the oxidation of fatty acids. Oxidation is the process by which the body metabolizes (breakdowns) complex molecules into simpler molecules. Individuals with FODs cannot convert dietary and stored fat into energy. Fat is a secondary source of energy for the body. The sugar glucose is the primary source of energy. However, when glucose has been used up, the body then breaks down fat to produce energy. FODs occur when certain enzymes required for the proper breakdown of fat are missing or functioning improperly, resulting the accumulation of fatty acids in various organ systems of the body.
Most FODs are also classified as mitochondrial diseases. The body breaks down fatty acids in the mitochondria, specialized structures found in most cells. Mitochondria release energy and produce more than 90% of the energy used by the body.
Fatty acid oxidation disorders are genetic disorders that result from mutations in certain genes, specifically genes that regulate the production of enzymes required for the proper breakdown of fatty acids. Mutation of one of these genes results in a deficiency of a certain enzyme, which, in turn, results in a failure to breakdown a specific fatty acid. Most of the known fatty acid oxidation disorders are inherited in an autosomal recessive manner.
Types of fatty acid oxidation disorders:
The number of disorders included under the heading fatty oxidation disorder has grown over the years as more research and advanced technology have identified new enzyme deficiencies. More than 20 disorders are now classified as FODs. Below is a list of some of the more recognized forms of FODs:
- 2,4 Dienoyl-CoA Reductase Deficiency
- Carnitine-Acylcarnitine Translocase Deficiency
- Carnitine Palmitoyl Transferase I & II Deficiency (CPT I & II)
- Glutaric Aciduria Type II (GA 2)
- Long Chain L-3-Hydroxyacyl-CoA Dehydrogenase (LCHAD) Deficiency
- Medium Chain Acyl-CoA Dehydrogenase (MCAD) Deficiency
- Primary Carnitine Deficiency
- Short Chain Acyl-CoA Dehydrogenase (SCAD) Deficiency
- Short Chain L-3-Hydroxyacyl-CoA Dehydrogenase (SCHAD) Deficiency
- Trifunctional Protein Deficiency (TFP)
- Very Long Chain Acyl-CoA Dehydrogenase (VLCAD) Deficiency
Symptoms associated with fatty acid oxidation disorders vary greatly, even among infants with the same type of FOD and even among individuals within the same family. Some individuals have few or mild symptoms; others develop severe symptoms. Many experience episodes of metabolic crisis (elevated levels of fatty acids in the body). Metabolic crisis often occurs when individuals do not eat (fast) for a period of time, approximately three to four hours for infants and up to eight hours for adults. Fasting increases the body's dependence on fatty acid oxidation for energy.
Some general symptoms common to most FODs include:
Without prompt diagnosis and treatment, a metabolic episode can result in serious, life-threatening complications. In severe cases of FODs, such symptoms may appear shortly after birth and may include encephalopathy (brain disease); skeletal myopathy (muscle disease); cardiomyopathy (heart muscle disease) and failure of an affected organ (e.g., liver failure). A variety of symptoms may occur secondary to these conditions including coma, developmental delays, chronic seizures, muscle weakness, heart failure or cardiac arrest.
Although FODs have common symptoms, affected children will not have all of the symptoms listed above. Different forms of FODs affect certain organs. For example, MCAD deficiency is associated with liver abnormalities, but rarely affects the heart. VLCAD deficiency is separated into two distinct forms: one affecting the heart and one affecting the liver. The mild form causes recurrent hypoglycemia.
Many infants with fatty acid oxidation disorders may be diagnosed through newborn screening, a process in which blood is taken from the heels of an infant. In infants with FODs, decreased activity of a particular enzyme may be detected in red blood cells.
An acylcarnitine profile test has become the test of choice in confirming a diagnosis of a FOD. During this test, blood or tissue samples are taken and studied to detect and analyze acylcarnitine, a substance that builds up in individuals with FODs. Each FOD has a unique acylcarnitine profile allowing physicians to confirm a diagnosis of a FOD and to determine which specific FOD is present.
Analysis of urine samples may reveal elevated levels of organic acids that may be indicative of a FOD. Prenatal diagnosis is possible through amniocentesis or chorionic villus sampling (CVS). Amniocentesis is a common prenatal procedure in which a small amount of amniotic fluid (the protective fluid that surrounds a fetus) is removed and studied. CVS is a procedure in which tissue samples are obtained from the placenta.
Treatment depends upon the specific form and severity of the disorder. All children with an FOD should avoid going long periods of time without eating. Children need to follow a low-fat, high-carbohydrate diet. Adherence to this diet may lead to an improvement of symptoms and slow the progression of the disorder. However, every child's response is different and some symptoms may still develop despite treatment.
Some children may receive supplementation with carnitine, a substance produced by the body that acts as a carrier of fatty acids to the mitochondria. The Food and Drug Administration (FDA) has approved Carnitor® (levocarnitine) for the treatment of primary carnitine deficiency in 1986. In 1992, the FDA approved Carnitor® for secondary carnitine deficiency of genetic origin. Carnitor® is a specialized form of carnitine and basic carnitine supplements sold in health food stores are not the same and should not be substituted for Carnitor® prescribed by a physician. Carnitor® is manufactured by Sigma-Tau Pharmaceuticals.
During a metabolic crisis aggressive medical therapy is necessary. Children should be hospitalized and receive a 10% glucose IV.
Fatty acid oxidation disorders have been diagnosed with greater frequency in the past couple decades because of better diagnostic technology and the medical community's growing knowledge and familiarity with these disorders. Prompt recognition and early treatment of these disorders is essential to preventing associated symptoms. However, some symptoms may still occur despite treatment and proper diet. Medical research is currently ongoing for many metabolic disorders including FODs and should lead to newer treatments and diagnostic options for affected infants and children.
Robert Tomaino is currently a freelance writer living in Danbury, CT. He graduated from the University of Richmond in 1994 with a degree in communications and journalism. Mr. Tomaino spent five years at the National Organization for Rare Disorders (NORD) where he started as a writer and became managing editor of the Information Services department. His responsibilities included writing and updating new and existing reports for NORD’s rare disease database, researching textbooks and medical databases for information on rare disorders, and developing working relationships with physicians across the country who are the leading experts concerning specific rare disorders. Mr. Tomaino also supervised a freelance writing team at NORD. After NORD, Mr. Tomaino worked at Enterprise Interactive, a business consulting firm, where he developed story ideas and researched various online sources for background information necessary to create news articles on topics related to e-commerce solutions, travel, and the Internet’s impact on business.
|Review Date: 5/6/2004|
Reviewed By: Reviewed By: Bibina J. Varughese, R.D., Pediatric Metabolic Nutritionist, Institute for Genetic Medicine, Saint Peter's Univ Hospital, New Brunswick, NJ.
Bibina Varughese, RD
Bibina J. Varughese is a Registered Dietitian with 12 years experience in Nutrition. Bibina graduated from The College of St. Elizabeth in Convent Station, NJ with her Bachelors degree in Home Economics.
Bibina has worked in the Metabolic field for 5 1/2 years at Saint Peter's University Hospital (SPUH), Institute for Genetic Medicine in NJ. Here she managed the diets of children and adults with Metabolic and Genetic disorders such as PKU, MSUD, Galactosemia, FOD, etc. At the metabolic center, Bibina has worked closely with families in providing diet education, obtaining authorizations for approval through insurance companies for special food and formula coverage, and providing nutritional (Metabolic) education to the State WIC nutritionist.
Bibina resigned from the Metabolic center, a full time position, as the metabolic dietitian and was working part time as a clinical dietitian at SPUH for the Department of Food and Nutrition. In this position, her main duty is to provide therapeutic nutritional education to patients with Diabetes, Heart Disease, Cancer, Prenatal, and others. However at the present time she has returned to the Metabolic Center at the Institute for Genetic Medicine for an interim period of time.
Prior to joining St. Peter's, she worked at Jersey Shore University Hospital in NJ. Her primary role was providing nutritional education to pediatric and cancer patients.
Bibina is a member of the American Dietetic Association and the New Jersey Dietetic Associations.