UBQLN2 and neurodegenerative disease: It is interesting to point out here the fact that the three genes for which there is evidence for an involvement in human neurodegenerative diseases, either potential or direct (UBQLN1, UBQLN2 and UBQLN4, see Introduction) have very similar UBA and UBL domains (see the small distances among them in Figure 3), encode structurally identical proteins and are related by successive duplications (UBQLN4 ➔ UBQLN1 ➔ UBQLN2).