Acid lipase disease is a name used to describe two related disorders of fatty acid metabolism. Acid lipase disease occurs when the enzyme needed to break down certain fats that are normally digested by the body is lacking or missing, resulting in the toxic buildup of these fats in the body’s cells and tissues. These fatty substances, called lipids, include waxes, oils, and cholesterol. Two rare lipid storage diseases are caused by the deficiency of the enzyme lysosomal acid lipase: