Carnitine palmitoyltransferase (CPT) are enzymes crucial for fat energy use. CPT helps move long-chain fatty acids into cells for fuel conversion. Without proper CPT function, the body struggles to access fat reserves, causing metabolic issues, especially during high energy demands.
The Role of CPT in Fat Metabolism
Body cells, especially muscle cells, use beta-oxidation to convert long-chain fatty acids into energy. These fatty acids cannot enter mitochondria, the cell’s “powerhouses,” directly. The carnitine shuttle system, with CPT enzymes, facilitates this.
The process starts in the cytoplasm where long-chain fatty acids are activated. Carnitine palmitoyltransferase I (CPT1), on the outer mitochondrial membrane, converts them into acylcarnitine, allowing passage across this membrane.
A transporter then moves acylcarnitine across the inner mitochondrial membrane into the mitochondrial matrix. Inside, carnitine palmitoyltransferase II (CPT2) converts acylcarnitine back into fatty acid form for beta-oxidation and cellular energy production.
Importance of CPT for Energy
Fat is a concentrated energy source, providing over twice the energy per gram compared to carbohydrates or protein. This makes fat stores, primarily triglycerides, the body’s largest and most efficient energy reserve, especially when glucose is scarce.
During prolonged exercise, fasting, or illness, glucose stores deplete, and the body shifts its energy reliance to fat. CPT’s proper function ensures these stored fats are efficiently accessed and converted into adenosine triphosphate (ATP), the body’s energy currency.
This ability sustains physical activity and maintains energy balance during reduced food intake. Without effective CPT activity, the body struggles to meet energy demands, leading to symptoms of energy deprivation.
When CPT Doesn’t Work Properly
When CPT enzymes are deficient, the body struggles to break down long-chain fatty acids for energy, leading to rare genetic metabolic disorders called fatty acid oxidation disorders. These manifest as CPT1 deficiency and CPT2 deficiency.
CPT1 deficiency primarily affects the liver and is detected shortly after birth via newborn screening. Symptoms appear during infancy, including low blood sugar (hypoglycemia) with low ketones, an enlarged liver, and nervous system damage from toxin buildup. Episodes are triggered by prolonged fasting or illness.
CPT2 deficiency has three main forms: lethal neonatal, severe infantile, and myopathic. The myopathic form, the least severe and most common, primarily affects muscles, causing recurrent episodes of pain, weakness, and breakdown (rhabdomyolysis), which can lead to dark urine. These episodes are triggered by strenuous exercise, fasting, or infections.
Diagnosis involves blood tests for abnormal compound levels, such as carnitine or specific fats. These deficiencies can be confirmed by genetic testing or by measuring enzyme activity.
Living with CPT Deficiencies
Managing CPT deficiencies involves dietary modifications and avoiding known triggers. Individuals are advised to follow a low-fat, high-carbohydrate diet, which reduces reliance on long-chain fatty acids for energy.
Frequent meals are also recommended to prevent prolonged fasting, which can trigger metabolic crises by depleting glucose stores and increasing fat metabolism demand. Avoiding strenuous exercise, extreme temperatures, and promptly managing infections are important strategies to prevent symptom onset.
In some cases, medium-chain triglyceride (MCT) oil may be prescribed as a supplemental energy source, as these fats do not require the CPT system for mitochondrial transport. Medical supervision by a metabolic specialist or dietitian is important to tailor management plans and address individual needs.