Primary carnitine deficiency

Synonyms

8

Overview

Primary carnitine deficiency is a genetic condition that prevents the body from using certain fats for energy, particularly during periods without food (fasting). The nature and severity of signs and symptoms may vary, but they most often appear during infancy or early childhood and can include severe brain dysfunction (encephalopathy), cardiomyopathy, confusion, vomiting, muscle weakness, and hypoglycemia. Some individuals may only have fatigability in adulthood, or no symptoms at all. This condition is caused by mutations in the SLC22A5 gene and is inherited in an autosomal recessive manner. Treatment and prevention of symptoms typically includes oral L-carnitine supplementation.

Symptoms

The list of signs and symptoms mentioned in various sources for Carnitine transporter deficiency may include:

    • Cardiomegaly
    • Coma
    • Confusion
    • Congestive heart failure
    • Decreased carnitine level in liver
    • Decreased plasma carnitine
    • Elevated hepatic transaminases
    • Encephalopathy
    • Endocardial fibroelastosis
    • Failure to thrive
    • Hepatic steatosis
    • Hepatomegaly
    • Hyperammonemia
    • Hypertrophic cardiomyopathy
    • Impaired gluconeogenesis
    • Lethargy
    • Muscular hypotonia
    • Myopathy
    • Recurrent hypoglycemia
    • Reduced muscle carnitine level
    • Somnolence
    • Vomiting

                                                                                        Causes

                                                                                        Mutations in the SLC22A5 gene cause primary carnitine deficiency. This gene provides instructions for making a protein called OCTN2 that transports carnitine into cells. Cells need carnitine to bring certain types of fats (fatty acids) into mitochondria, which are the energy-producing centers within cells. Fatty acids are a major source of energy for the heart and muscles. During periods of fasting, fatty acids are also an important energy source for the liver and other tissues.

                                                                                        Mutations in the SLC22A5 gene result in an absent or dysfunctional OCTN2 protein. As a result, there is a shortage (deficiency) of carnitine within cells. This deficiency, as well as potential build-up of fatty acids within the cells, causes the signs and symptoms of the condition.

                                                                                        Prevention

                                                                                        Primary carnitine deficiency is inherited in an autosomal recessive manner. Individuals have two copies of each gene, one of which is inherited from each parent. For an individual to have an autosomal recessive condition, he/she must have a mutation in both copies of the disease-causing gene. The parents of an affected individual, who each likely have one mutated copy, are referred to as carriers. Carriers typically do not have any signs or symptoms of the condition. When two carriers for an autosomal recessive condition have children together, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier like each of the parents, and a 25% risk to not have the condition and not be a carrier.

                                                                                        Diagnosis

                                                                                        The first suspicion of SPCD in a patient with a non-specific presentation is an extremely low plasma carnitine level. When combined with an increased concentration of carnitine in urine, the suspicion of SPCD can often be confirmed by either molecular testing or functional studies assessing the uptake of carnitine in cultured fibroblasts.

                                                                                        Identification of patients presymptomatically via newborn screening has allowed early intervention and treatment.

                                                                                        Prognosis

                                                                                        Infantile metabolic and childhood myopathic presentations of the condition can be fatal if untreated. However, long-term prognosis is excellent with oral carnitine supplementation. If the disorder goes unrecognized, death can occur due to cardiac failure, arrhythmias or sudden death. Hypoglycemia or sudden deaths from arrhythmias (even without cardiomyopathy) have been reported in affected individuals who stop their carnitine supplementation against medical advice.

                                                                                        Treatment

                                                                                        Most individuals with primary carnitine deficiency are followed by a metabolic doctor as well as a dietician familiar with this condition. Certain treatments may be advised for some children but not others. Treatment is often needed throughout life. The main treatment for this condition is lifelong use of L-carnitine, which is a natural substance that helps body cells make energy. It also helps the body get rid of harmful wastes. L-carnitine can reverse the heart problems and muscle weakness caused by this condition.

                                                                                        In addition to L-carnitine, infants and young children with primary carnitine deficiency need to eat frequently to prevent a metabolic crisis. In general, it is often suggested that infants be fed every four to six hours. But some babies need to eat even more frequently than this. Many teens and adults with this condition can go without food for up to 12 hours without problems. Some children and teens benefit from a low-fat, high carbohydrate diet. Any diet changes should be made under the guidance of a metabolic specialist and/or dietician familiar with this condition. Ask your doctor whether your child needs to have any changes in his or her diet. Other treatments usually need to be continued throughout life.

                                                                                        Infants and children with this condition need to eat extra starchy food and drink more fluids during any illness, even if they may not feel hungry, because they could have a metabolic crisis. Children who are sick often do not want to eat. If they won’t or can’t eat, they may need to be treated in the hospital to prevent serious health problems.

                                                                                        Approved therapies:
                                                                                        Levocarnitine (Carnitor) - FDA-approved indication: Treatment of primary and secondary carnitine deficiency. 

                                                                                        Resources

                                                                                        Refer to Research Publications.