BETA-AMYLOID PRECURSOR PROTEIN MESSENGER-RNA IS INCREASED IN INCLUSION-BODY MYOSITIS MUSCLE

VACUOLATED muscle fibers in muscle biopsies of 8 out of 8 inclusion bo dy myositis (IBM) patients, including 2 hereditary patients, manifeste d increased mRNA for the beta-amyloid precursor protein (betaAPP) that contains Kunitz-type protease inhibitor motif. In affected fibers, in creased betaAPP-mRNA corresponded to abnormally accumulated betaAPP im munoreactivity (including beta-amyloid protein epitope). In normal hum an muscle fibers increased betaAPP-mRNA was present only at the neurom uscular junctions. Our study (a) suggests that abnormally accumulated betaAPP in IBM vacuolated fibers results, at least partly, from increa sed betaAPP generation, and (b) provides the first demonstration of up -regulated betaAPP-mRNA in pathologic human tissue other than brain of Alzheimer's disease and Down's syndrome.