Transcriptional misreading of dinucleotide repeats that generates deletions in RNA and produces frame-shift proteins with loss of function has been reported in Alzheimer's disease (AD). Here frame-shift ubiquitin-B and amyloid precursor protein were immunochemically shown to exist in the brain of high pathology control (HPC) patients with AD pathology but without prior dementia. These proteins were absent in low pathology control patients with limited AD pathology and no dementia. Since the HPC patients can be regarded as preclinical AD patients, our results suggest the accumulation of these proteins involved in the initial steps of AD pathogenesis. By contrast, complement proteins were detected in the AD patients, whereas only trace amounts were found in the HPC patients, indicating the involvement of complement proteins in the later stage of AD dementia. (C) 2003 Elsevier Ireland Ltd. All rights reserved.