UBE2I and Alzheimer disease: Interestingly, one study described decreased SUMO1 and Ubc9 mRNA levels in cortices of wild‐type mice aged 3–15 months (Akar & Feinstein, 2009), contrasting with another study describing increased Ubc9 protein expression levels without changes in mRNA levels in non‐AD mouse brains within the same age range (Nistico et al., 2014).