APP and Alzheimer disease: Therefore, scant and conflicting data are available on abundance and processing of the Aβ parent molecule in AD-affected brains [148–151]: APP751 and APP770 isoform patterns were found to be unchanged but concentrations of total APP and fragment APP695 decreased on mRNA level [150] and protein level [151] with an increase of the Aβ peptide level in samples of the frontal cortex of AD cases [151].