Representative mass spectra showing C-terminally truncated Aβ peptides immunoprecipitated from cerebrospinal fluid using antibody 6E10. (A) Representative Aβ isoform pattern in a control individual. (B) Representative Aβ isoform pattern in a patient with sporadic Alzheimer's disease. (C) Representative Aβ isoform pattern in a carrier of the FAD-associated PSEN1 A431E mutation.