UBQLN1 and Alzheimer disease: For instance, some studies have indicated that ubiquilin-1 is a ubiquitin protein that inhibits neuronal APP aggregation in vitro and vivo [72,106,107,108]; however, in the brains of AD patients, ubiquilin-1 levels were significantly reduced, along with the accumulation of APP, which in turn promoted the production and deposition of Aβ.