The present invention relates to a polypeptide having an amino acid sequence comprising at least two substitutions of the glycine residues in one or more GXXXG motives in the amino acid sequence of the wild type Aβ peptide as depicted in SEQ ID NO:1. Furthermore the present invention relates to methods and a kit for diagnosing a neurodementing disease. The present invention further relates to the polypeptide for use as a medicament in human and veterinary medicine and as a diagnostic substance, in particular for use as a medicament for the prevention and for the diagnosis of the progression of Alzheimers disease, Downs syndrome, Dementia with Lewy bodies, fronto-temporal dementia, misfolded protein/peptide related diseases, cerebral amyloid angiopathy, Prion disease and amyloidoses.
