Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is an inherited disorder that is caused by having inadequate amount of the enzyme VLCAD needed to break down certain fats into energy. The symptoms of VLCAD deficiency usually start after a long period of time without eating or during illness. VLCAD deficiency includes three different forms. Infants with early-onset form, the most severe and common form of VLCAD deficiency, show heart enlargement, liver enlargement, low blood sugar, and low muscle tone in the first months of life. This form is fatal if not treated. Some individuals show symptoms starting in early childhood that include liver enlargement and low blood sugar, but no heart problems. Individuals with the late-onset form, the mildest form, develop muscle disease during adulthood. With early detection of this condition, proper management by a special diet, and avoidance of fasting, individuals with VLCAD deficiency usually have normal physical and mental development. pathogenic variants in the ACADVL gene cause VLCAD deficiency.