Human BCS1-like (BCS1L),a mitochondrial inner-membrane protein,is a chaperone necessary for the assembly of mitochondrial respiratory chain complex III. Recently studies indicated that the mutations in this protein may cause the GRACILE (growth retardation,aminoaciduria,cholestasis,iron overload,lactacidosis,and early death) syndrome,a recessively inherited lethal disease characterized by fetal growth retardation,lactic acidosis,aminoaciduria,cholestasis,and abnormalities in iron metabolism.