Carnitine palmitoyltransferase I deficiency is a rare metabolic disorder that prevents the body from converting certain fats called long-chain fatty acids(LCFA) into energy, particularly during periods without food.

[citation needed] Carnitine, a natural substance acquired mostly through the diet, is used by cells to process fats and produce energy.

People with this disorder have a faulty enzyme, carnitine palmitoyltransferase I, that prevents these long-chain fatty acids from being transported into the mitochondria to be broken down.

Without this enzyme, long-chain fatty acids from food and fats stored in the body cannot be transported into mitochondria to be broken down and processed.

As a result, excessive levels of long-chain fatty acids may more rapidly build up in tissues, damaging the liver, heart and/or brain.