Carnitine-acylcarnitine translocase (CACT) deficiency is one of the most severe disorders of fatty acid oxidation associated with a high mortality at the initial presentation or during the first year of life. Onset is typically in the early newborn period with features that include cardiomyopathy, arrhythmias, liver dysfunction and skeletal muscle damage. In a significant proportion of cases sudden, unexplained death, presumably due to arrhythmia is the first sign of disease. A minority of patients have a later onset with a milder clinical phenotype and there are a few reports of long-term survival after starting an intensive treatment protocol. There is a patient reported who has been treated since birth and is asymptomatic at 4.5 years.