What Is Primary Carnitine Deficiency?

Primary carnitine deficiency, caused by mutations in the SLC22A5 gene, is a condition in which the body cannot properly process fats into energy. This results in a defect in the protein that transports carnitine, a natural substance derived from an amino acid. Without early detection and treatment, the condition can cause permanent brain damage and can be fatal.

If left untreated, primary carnitine deficiency causes a weakening of the heart muscles, leading to a diminished ability to pump blood around the body, and enlargement of the heart muscles (cardiomyopathy). The liver may also become enlarged. This condition can also cause a weakness in skeletal muscles and dangerously low blood sugar (hypoglycemia) that can lead to brain damage. While this brain damage can cause irreversible learning problems or even intellectual disability, the remaining symptoms tend to disappear once an individual begins taking L-carnitine supplements.

Without supplements, an individual with primary carnitine deficiency is particularly vulnerable to "metabolic crisis" (including sleepiness, irritability, fever, nausea, vomiting, and/or low blood sugar) when they go long periods without eating (fasting) or are ill. If left untreated, the metabolic crisis can lead to seizures, swelling of the brain, and other life-threatening symptoms.

How Common Is Primary Carnitine Deficiency?

Primary carnitine deficiency affects approximately 1 in 100,000 newborns. It is more common in Japan, where the incidence is 1 in 40,000, and in the Faroe Islands, where the prevalence is 1 in 300.

How Is Primary Carnitine Deficiency Treated?

Individuals with primary carnitine deficiency will need to take supplements of L-carnitine for their entire lives. If children have begun to experience heart problems or muscle weakness, they can typically reverse those symptoms by taking L-carnitine. A physician may also recommend that individuals with primary carnitine deficiency eat more frequently, even if they do not feel hungry. This is particularly important when they are young and/or sick.

What Is the Prognosis for an Individual with Primary Carnitine Deficiency?

The prognosis for an individual with primary carnitine deficiency is very good when treatment is started at birth. These individuals can typically live normal lives. If treatment is not started early enough, children may experience permanent brain damage, leading to learning difficulties or even intellectual disability. Without any treatment, the disease causes numerous health issues and can be fatal.

Additional Considerations for Carriers

Carriers of fatty-acid oxidation defects, including primary carnitine deficiency, do not typically show symptoms of the disease. However, there may be an increased risk of serious pregnancy complications, particularly in the third trimester, in women carrying a fetus affected with a fatty-acid oxidation defect. A woman whose pregnancy may be affected by a fatty-acid oxidation defect, such as primary carnitine deficiency, should speak with her physician for recommendations and may benefit from consultation with a high-risk physician.

Other names for
primary carnitine deficiency

  • CDSP
  • Carnitine transport defect
  • Carnitine uptake defect
  • Systemic carnitine deficiency


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