MAPT and Alzheimer disease: Whilst the CSF Ab1-42 was depressed (371 pg/ml, reference range 627–1,322) possibly reflecting sequestration within CNS amyloid plaques as is seen in Alzheimer’s disease (AD), unlike in AD the CSF tau level was also low (107 pg/ml, reference range 146–595) mitigating against an ongoing neurodegenerative process.