Interestingly, other RNA-binding proteins, including the involved-in-DM1 splicing factor Muscleblind (Mbl) (Llamusi et al., 2013) and fragile X-related protein 1 (FXR1) (Khandjian et al., 1998; Mientjes et al., 2004; Whitman et al., 2011), are expressed in sarcomeres. The gene discussed is FXR1; the disease is myotonic dystrophy type 1.