Carnitine palmitoyltransferase II (CPT II) deficiency is an inherited disorder in which the body is defective in using certain fats for energy. There are three main types of CPT II deficiency. The first type is the most severe. Symptoms may appear soon after birth, including respiratory failure, seizures, liver failure, weakened heart muscles, irregular heartbeat, brain and kidney abnormalities, low blood sugar levels and a low level of ketones. Individuals affected with this form of CPT II deficiency usually live for a few days to a few months. In the second type, symptoms appear within the first year of life, including an enlarged liver, weakened heart, irregular heartbeat, seizures, low blood sugar levels and a low level of ketones. These problems are often triggered by periods without food (fasting) or illness. Individuals affected with this form of CPT II deficiency are at risk for liver failure, nervous system damage, coma, and sudden death. The third type is the least severe type of CPT II deficiency. Symptoms may appear in infancy, childhood or adulthood. Individuals with this form of CPT II deficiency experience recurrent episodes of muscle pain and weakness after exercise, stress, exposure to extreme temperatures, infections or fasting. In between these episodes, the affected individuals are often symptom free. Generally, intellectual conditions are not affected by CPT II deficiency. Currently, there are no effective treatments for CPT II deficiency. However, the symptoms can be alleviated if the affected individual avoids fasting and exercise, and manages nutrition intake properly. CPT II deficiency is caused by pathogenic variants in the CPT2 gene.