HSP90AA1 and scrapie: We present here the first gene expression analysis of four members of the HSP27 (HSPB1), HSP70 (the constitutive form HSP72/HSPA1A and the inducible HSP73/HSPA8), and HSP90 (the inducible form, HSP90AA1) gene families, their protein expression profiles, and their distribution in the central nervous systems of sheep naturally infected with clinical-stage scrapie.