Fatty Acid Oxidation disorders
Fatty acid oxidation disorders are inherited metabolic conditions that affect the breakdown of certain fats (fatty acids). The body breaks down fatty acids to release energy by a process called oxidation. This process has many steps, each driven by a different enzyme. Each fatty acid oxidation disorder results from a deficiency (lack) of one of these enzymes. The main disorders are:
- medium chain acyl-CoA dehydrogenase deficiency (MCADD)
- very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD)
- multiple acyl-CoA dehydrogenase deficiency (MADD) (= glutaric aciduria type II, GA II)
- long-chain hydroxyacyl-CoA dehydrogenase deficiency (LCHADD)
- mitochondrial trifunctional protein (MTP) deficiency
- carnitine palmitoyl-transferase I (CPT I) deficiency
- carnitine palmitoyl-transferase II (CPT II) deficiency
- carnitine acylcarnitine translocase deficiency
- carnitine transporter deficiency (= primary carnitine deficiency).
Last updated November 2014 by Dr A Morris, Consultant in Paediatric Metabolic Medicine, Genetic Medicine, St Mary’s Hospital, Manchester, UK.
The symptoms of these conditions vary and depend on the type of fatty acid oxidation disorder. In most of the disorders, problems occur in early childhood, usually brought on by minor infections associated with vomiting or fasting (not eating). At these times, the patients may become increasingly drowsy with low blood sugar levels. Without treatment, this can lead to seizures, coma or sudden death. Other patients may have problems affecting their heart (cardiomyopathy) or muscles. Some patients suffer episodes of muscle pain and damage (called rhabdomyolysis); these episodes may be brought on by exercise in adults who have had no problems during childhood.
Fatty acid oxidation disorders are genetic conditions. They are caused by faults (mutations) in the genes for the enzymes listed above.
The most common of the fatty acid oxidation disorders is MCADD. In the UK, this is diagnosed by newborn screening. The test is carried out on a few drops of blood from a heel prick.
Other fatty acid oxidation disorders are diagnosed by looking for abnormal chemicals in blood and urine if a patient has relevant symptoms.
Patients with MCADD need to avoid fasting and to maintain a regular intake of sugar during infections. The sugar can be given in drinks or intravenously if the patient vomits. With this simple management, outcomes are excellent.
Children with other fatty acid oxidation disorders also need to avoid fasting and to receive plenty of sugar during infections. For some disorders, extra measures are needed. These may include a low-fat diet, overnight feeds or drugs (such as carnitine, riboflavin or bezafibrate).
Fatty acid oxidation disorders are inherited in an autosomal recessive manner.
Prenatal diagnosis is available for these disorders. Affected families should be referred to their regional genetics centre for further information and support.
Information and support in the UK for fatty acid oxidation disorders is provided by Climb (see entry Inherited Metabolic diseases).