PSEN1 and Alzheimer disease: PS1 is the catalytic component of the γ-secretase complex participating in both amyloidogenic and non-amyloidogenic pathways of APP processing; thus, β-amyloid (or Aβ), the AD triggering effector [15,16], is a proteolytic peptide generated by processing of APP by successive action of two enzymes, β-secretase and γ-secretase (for a review, see [17]).