UBQLN2 and amyotrophic lateral sclerosis: The proteasomal shuttle factor ubiquilin 2 (UBQLN2) contains the N-terminal ubiquitin-like (UBL) and C-terminal UBA domains, and mutations in the Pro-rich (PXX) region of UBQLN2 cause dominant X-linked ALS and ALS/dementia (Figure 4B) (Deng et al., 2011).