Gamma-secretase subunit PEN-2, or Presenilin-2, is an essential regulatory component of the gamma-secretase complex, which is a protease complex responsible for the proteolysis of transmembrane proteins such as Notch and the amyloid precursor protein, implicated in human diseases such as Alzheimer’s disease (Francis et al. 2002). The gene discussed is APP; the disease is early-onset autosomal dominant Alzheimer disease.