Mutations in the UBQLN2 gene (located on the X chromosome), encoding ubiquilin 2, have been identified in ALS-FTD patients (Deng et al., 2011b; Williams et al., 2012), at frequencies of 0.5%–2% of fALS cases and 0.4% of SALS cases, with reduced penetrance in females (Deng et al., 2011b; Daoud et al., 2012; Williams et al., 2012; Gellera et al., 2013). Here, UBQLN2 is linked to frontotemporal dementia.