Carnitine palmitoyltransferase II deficiency (CPT II deficiency) is an inherited disorder that affects the body's ability to break down long-chain fatty acids. It is caused by a deficiency of the enzyme carnitine palmitoyltransferase II (CPT II). This enzyme is responsible for transporting long-chain fatty acids into the mitochondria, where they can be broken down and used for energy. Without this enzyme, long-chain fatty acids cannot be broken down and accumulate in the body, leading to a variety of symptoms. Symptoms of CPT II deficiency can include muscle weakness, fatigue, poor feeding, and seizures.