Reappraisal of ultrastructural diversity of amyloid plaques in Gerstmann-Sträussler-Scheinker syndrome.

Gerstmann-Sträussler-Scheinker (GSS) syndrome is one of the most rare human neurodegenerative disease. In this report I summarise the ultrastructural pathology of amyloid plaques in two cases of this rare disease. The first type, unicentric "kuru" plaques consisted of stellate arrangements (stars or cores) of amyloid bundles emanating from a densely interwoven centre. Amyloid stars were surrounded by astrocytic processes and invaded by microglial cells. The amyloid bundles were attached to microglial cell membranes. Of note, robust basement membranes lined with electron dense astrocytic anchorages material were observed at the periphery of almost all amyloid plaques. Dystrophic neurites (DN) were seen only rarely. Occasionally, clusters composed of several kuru plaques were found; those are interpreted as intermediate forms to multicentric plaques which consisted of several merging stellate cores. In contrast to kuru plaques associated with a limited number of DN, numerous such structures were seen at the periphery of multicentric plaques. Identical DN were observed not associated with any plaques. The last and the rarest type of plaques, were purely neuritic plaques. These consisted of large areas filled with DN of different sizes and shapes (sometimes bizarre) but not amyloid bundles. Analogously to kuru and multicentric plaques, astrocytic processes were observed at the periphery.