PSMC4 and Brain atrophy: This has been particularly well exemplified in animal models, notably mice in which knockout of the subunit genes Psmd4, Psmd11, Psmg1, Psmc3, and Psmc4 is embryonic lethal (Table 3).108, 109, 110, 111 Inevitably, conditional knockout of the Psmg1, Psmc1, Psmc4, Psmd4, and Psmd14 genes have been associated with severe neurological phenotypes characterized by brain atrophy, malformations, neurodegeneration, or neuron loss in various mouse and/or Drosophila models.39