Carnitine palmitoyltransferase I (CPT-I) deficiency
CPT-I deficiency is inherited in an autosomal recessive pattern. Normally a person has two functional CPT-1A genes. In people with CPT-I deficiency, both genes have a mutation and there is a deficiency of the critical enzyme activity. Each parent of a newborn with CPT-I deficiency typically has one functional and one mutated gene and is considered a carrier. When both parents are carriers, the chance of a newborn inheriting two mutated genes is 25%.
Carriers of CPT-I deficiency do not typically have symptoms. However, a mother who is pregnant with a baby with CPT-I deficiency is at risk of illness during pregnancy. The mother may develop AFLP (acute fatty liver of pregnancy).
The symptoms of CPT-I are variable from one individual to the next. The first symptom of CPT-I deficiency, hypoketotic hypoglycemia (low ketones and low blood sugar), usually begins before 2 years of age during an illness (fever or vomiting). Other symptoms may include liver dysfunction, hepatomegaly (enlarged liver), muscle weakness, cardiomyopathy (heart muscle disease) and rhabdomyolysis (breakdown of muscle). There is also an adult onset form of CPT-I that causes myopathy (muscle disease).
- Incidence: CPT-I deficiency is rare. There have been about 50 patients reported in the literature. It is more common in the Inuit and Hutterite populations.
- New York State Method of Screening (First Tier): Screening for CPT-I deficiency is accomplished by measuring the ratio of acylcarnitines C0/C16+C18 by tandem mass spectrometry (MS/MS).
- Second Tier Screening: None
- Testing can be affected by: Screening may be normal in patients who received IV glucose or who were not ill when the specimen was collected.
- Interpretation/reporting of data: Results are reported as within acceptable limits, borderline or as a referral. A repeat specimen should be collected for a borderline result. Prompt consultation with a specialist is required for a referral.
- Referral to Specialty Care Center: Patients with an abnormal newborn screen for CPT-I deficiency are referred to an Inherited Metabolic Disorder Specialty Care Center for evaluation by a biochemical geneticist trained in the diagnosis and treatment of CPT-I deficiency.
Diagnostic testing may include quantification of total and free carnitines, Creatine Kinase (CK), liver enzymes, molecular genetic analysis of the CPT-1A gene and fatty acid oxidation studies on fibroblasts (skin cells).
Treatment is dietary, including avoidance of fasting, a high-carbohydrate, low fat diet and supplementation with medium-chain triglycerides (MCT) as a source of supplemental calories. Treatment for cardiac involvement or rhabdomyolysis is supportive. During times of illness, hospitalization may be required to monitor and treat hypoglycemia. Some physicians may recommend consuming uncooked cornstarch before bedtime.
Prognosis is variable and dependent on multiple factors, including the severity of disease and response to treatments.
Carnitine palmitoyltransferase I (CPT-I) deficiency is a fatty acid oxidation disorder (inherited metabolic disorder).
CPT-I deficiency is caused by mutations in the CPT-1A gene. Individuals with this disorder are unable to convert certain fats to energy and may develop symptoms during times of high energy need such as fasting or illness.