UBQLN2 and amyotrophic lateral sclerosis: Most ALS-associated mutations in UBQLN2 are clustered within 42-amino acid proline-rich repeat (PRR) that is unique to UBQLN2 (Deng et al., 2011) however, disease-linked mutations outside this region have also been described (Synofzik et al., 2012; Daoud et al., 2012).