The IDP class includes the β-amyloid peptide (Aβ) as one of the sequential proteolysis products of amyloid precursor protein (APP) in Alzheimer’s disease (AD), tau protein in AD and other tauopathies, α-synuclein in Parkinson’s disease (PD), and islet amyloid polypeptide (IAPP) in type II diabetes (Figure 1). The gene discussed is APP; the disease is Parkinson disease.