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Fatty Acid Oxidation Disorders

By

Matt Demczko

, MD, Sidney Kimmel Medical College of Thomas Jefferson University

Last full review/revision Apr 2020| Content last modified Apr 2020
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Fatty acid oxidation disorders are lipid metabolism disorders that are caused by a lack or deficiency of the enzymes needed to break down fats, resulting in delayed mental and physical development. Fatty acid oxidation disorders occur when parents pass the defective genes Genes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells... read more Genes that cause these disorders on to their children.

Fats Fats Carbohydrates, proteins, and fats supply 90% of the dry weight of the diet and 100% of its energy. All three provide energy (measured in calories), but the amount of energy in 1 gram (1/28 ounce)... read more (lipids) are an important source of energy for the body. The body’s store of fat is constantly broken down and reassembled to balance the body’s energy needs with the food available. Several enzymes help break down fats so that they may be turned into energy.

Children who have one of these disorders are missing or have a deficiency of the enzymes needed to break down (metabolize) fats. The lack of these enzymes leaves the body short of energy and allows breakdown products, such as acyl-CoA, to accumulate. The enzyme most commonly deficient is medium-chain acyl-CoA dehydrogenase Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency Fatty acid oxidation disorders are lipid metabolism disorders that are caused by a lack or deficiency of the enzymes needed to break down fats, resulting in delayed mental and physical development... read more (MCAD). Other enzyme deficiencies include short-chain acyl-CoA dehydrogenase (SCAD) deficiency, long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency Fatty acid oxidation disorders are lipid metabolism disorders that are caused by a lack or deficiency of the enzymes needed to break down fats, resulting in delayed mental and physical development... read more , very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency Fatty acid oxidation disorders are lipid metabolism disorders that are caused by a lack or deficiency of the enzymes needed to break down fats, resulting in delayed mental and physical development... read more , glutaric acidemia type II Glutaric acidemia type II Fatty acid oxidation disorders are lipid metabolism disorders that are caused by a lack or deficiency of the enzymes needed to break down fats, resulting in delayed mental and physical development... read more , and mitochondrial trifunctional protein (TFP) deficiency. Most of these disorders begin in infancy.

Treatment of fatty acid oxidation disorders varies depending on the type of fatty substances that accumulate in the blood and tissues.

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency

This disorder is one of the most common inherited disorders of metabolism, particularly among people of Northern European descent.

Symptoms of MCAD deficiency usually develop after 2 to 3 months of age. Children are most likely to develop symptoms if they go without food for a period of time (which depletes other sources of energy) or have an increased need for calories because of exercise or illness. The level of sugar (glucose) in the blood drops significantly (hypoglycemia), causing confusion or coma. Children become weak and may have vomiting or seizures. Over the long term, children have delayed mental and physical development, an enlarged liver, heart muscle weakness, and an irregular heartbeat. Sudden death may occur.

Since 2007, nearly every state in the United States has required that all newborns be screened for MCAD deficiency with a blood test. Tests of the urine and other tissues may also be done. DNA testing can be done to confirm the diagnosis.

Immediate treatment of an MCAD deficiency attack is with dextrose given by vein. For long-term treatment, children must eat often, never skip meals, and consume a diet high in carbohydrates and low in fats. Supplements of the amino acid carnitine may be helpful. Cornstarch may need to be given at night to prevent the level of glucose in the blood from getting too low. The long-term outcome is generally good.

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency

This deficiency is the second most common fatty acid oxidation disorder. It causes symptoms similar to those caused by MCAD deficiency. People may also have progressive impairment of the structure and function of the muscular walls of the heart chambers (cardiomyopathy Overview of Cardiomyopathy Cardiomyopathy refers to progressive impairment of the structure and function of the muscular walls of the heart chambers. There are three main types of cardiomyopathy: Dilated cardiomyopathy... read more Overview of Cardiomyopathy ), damage to the nerves of the hands and feet, and abnormal liver function. When children exert themselves, such as when exercising, the muscle tissue may become destroyed (rhabdomyolysis) and the damaged muscles may release the protein myoglobin, which turns the urine brown or bloody (myoglobinuria).

A woman whose fetus has LCHAD deficiency often has hemolysis (the breakdown of red blood cells), elevated levels of liver enzymes (indicating liver damage), and a low platelet count (called HELLP syndrome HELLP syndrome Preeclampsia is new high blood pressure or worsening of existing high blood pressure that is accompanied by excess protein in the urine and that develops after the 20th week of pregnancy. Eclampsia... read more ) while pregnant.

Doctors diagnose LCHAD deficiency by testing the blood for certain acids. Tests of skin cells are done to look for levels of certain enzymes. Genetic testing Genetic Screening Genetic screening is used to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder. Hereditary genetic disorders are disorders of chromosomes or... read more , which is used to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder, is also available.

Immediate treatment of an LCHAD deficiency attack is with hydration and glucose given by vein, bed rest, and supplements of the amino acid carnitine. For long-term treatment, children must eat often, avoid strenuous exercise, and consume a diet high in carbohydrates. Children are also given supplements of triglycerides.

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency

This deficiency is similar to LCHAD deficiency, but people typically have severe cardiomyopathy.

Glutaric acidemia type II

Doctors diagnose glutaric acidemia type II by analyzing the blood to look for a buildup of certain molecules. Tests of skin cells are done to look for levels of certain enzymes. Genetic testing is also available.

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