DUX4 target gene expression is very low in blood from ~700 individuals until ~ 20 years of age (within typical FSHD onset range) but then increases and persists through life (unpublished observations), suggesting an age‐dependent mechanism, such as telomere shortening (Stadler et al, 2013). The gene discussed is DUX4; the disease is facioscapulohumeral muscular dystrophy.