DUX4 and facioscapulohumeral muscular dystrophy: The non-canonical polyadenylation sequence in the pLAM region (exon 3) of DUX4 is the result of a critical single nucleotide polymorphism (SNP) that determines pathogenicity of a permissive 4qA allele5, and has long been associated with FSHD, likely through the stabilization of the resulting DUX4-fl mRNA17.