HTT and Alzheimer disease: Lysosomal proteases, including the cathepsins27, are central enzymes that are involved in the proteolytic degradation of misfolded and aggregation-prone proteins, such as amyloid-β (Aβ) and polyglutamine (polyQ)-expanded huntingtin (HTT), the contributing factors in the pathogenesis of Alzheimer’s disease and Huntington’s disease60,61, respectively.