Carnitine Deficiency – certain fats cannot be utilized for energy, particularly during periods of fasting. Carnitine, a natural substance acquired mostly through the diet, is used by cells to process fats and produce energy. Clinical symptoms typically appear during infancy or early childhood and can include severe brain dysfunction (encephalopathy), a weakened and enlarged heart (cardiomyopathy), confusion, vomiting, muscle weakness, and low blood sugar (hypoglycemia). The severity of this condition varies among affected individuals. Individuals with this disorder are at risk for heart failure, liver problems, coma, and sudden death. Treatment includes avoidance of fasting and carnitine supplementation.
https://ghr.nlm.nih.gov/condition/primary-carnitine-deficiency#diagnosis