In Alzheimer disease, histopathology typically reveals extracellular accumulations of amyloid beta (Abeta) in senile plaques and intracellular neurofibrillary tangles of hyperphosphorylated tau (P-tau). A[beta]42 is the 42 amino acid isoform of amyloid beta. Using positron emission tomography several studies found an inverse correlation between brain amyloid load and CSF A[beta]42.