Cholesterol ester storage disease and Wolman disease are recessive autosomal disorders caused by a deficiency in lysosomal acid lipase (LAL), also known as cholesteryl ester hydrolase.{26282,26283} 4-Methylumbelliferyl palmitate (4-MU palmitate) is a fluorogenic substrate for LAL.{26284} It may also be cleaved by other acid lipases.{26285,26286} Recent advances allow the assessment of LAL activity in very small blood volumes using 4-MU palmitate.{26282,26283}