DUX4L9 and facioscapulohumeral muscular dystrophy: The transcriptional target genes of DUX4 (the FSHD causal gene) and of DUX4c (also increased in FSHD muscles) identified to date cannot explain the cytoplasmic alterations observed in FSHD muscle sections, which show a higher number of splitting and branching myofibril bundles, as well as myofibril loss and sarcomere dysfunction [71–73] (Lancelot et al. in preparation).