PRION PROTEIN IS ABNORMALLY ACCUMULATED IN INCLUSION-BODY MYOSITIS

IN muscle biopsies of 8 sporadic inclusion-body myositis (S-IBM) and 4 hereditary inclusion-body myopathy (H-IBM) patients, vacuolated muscl e fibers contained within their vacuoles strongly immunoreactive inclu sions with 2 polyclonal and 1 monoclonal antibodies against prion prot ein (PrP). By light-microscopy, PrP deposits co-localized with beta-am yloid protein (A beta) and ubiquitin (Ub). By immuno-electronmicroscop y, both PrP and A beta were present on amorphous material and on 6-10 nm amyloid-like fibrils; and PrP and Ub co-localized on cytoplasmic tw isted tubulofilaments (TTFs) and on amorphous material. Our study prov ides the first demonstration of abnormally accumulated PrP in patholog ical tissue other than brain, and it suggests that PrP may play a role in the pathogenesis of IBM.