A novel assay for lysosomal pepstatin-insensitive proteinase and its application for the diagnosis of late-infantile neuronal ceroid lipofuscinosis

A highly sensitive assay for mammalian lysosomal pepstatin-insensitive prot einase (LPIP) is described using a synthetic peptide substrate coupled to a minotrifluoromethyl coumarin (AFC). LPIP is an endocarboxyl proteinase whic h has specific sequence requirements of Phe-Phe around the carboxyl termina l. This HPLC based assay can detect patients suffering from late-infantile neuronal ceroid lipofuscinosis (LINCL) and also heterozygote carriers in cu ltured lymphoid cells and skin fibroblasts. None of the patients analyzed h ad detectable enzyme activity confirming the defective gene product, while carriers had about 50% activity when compared with the normal controls. Neu rological controls comprised of patients with other neurodegenerative disor ders have LPIP activities similar to normal controls. LPIP activity is also detectable in amniocytes and chorionic villi. Thus the assay reported can also be used for prenatal diagnosis of LINCL. (C) 1999 Elsevier Science B.V . All rights reserved.