DUX4 and facioscapulohumeral muscular dystrophy: Transcriptional profiling studies have inferred the presence of DUX4 protein due to its “fingerprint” of elevated target genes in FSHD biopsies15, however DUX4 must be rare, or expressed at low levels, or both, as fingerprint genes are expressed at extremely low levels in most FSHD samples (FPKM = 0 in many cases), and a consortium of genes is necessary to detect an effect, averaged over many samples.