APP and early-onset autosomal dominant Alzheimer disease: APP gencDNA transcripts in plasma are derived from damaged brain cells; since the accumulation of Aβ begins as early as 20 years before the onset of dementia and Aβ itself is cytotoxic, the release of APP gencDNA transcripts may start at a relatively early clinical stage, that is the pre-clinical stage, of Alzheimer's disease.