This gene is located within a D4Z4 repeat array in the subtelomeric region of chromosome 4q. The D4Z4 repeat is polymorphic in length and a similar D4Z4 repeat array has been identified on chromosome 10. Each D4Z4 repeat unit has an open reading frame (named DUX4) that encodes two homeoboxes; the repeat-array and ORF is conserved in other mammals. There is no evidence for transcription of the gene at this locus though RT-PCR and in vitro expression experiments indicate that a telomeric paralog of this gene is transcribed in some haplotypes. Contraction of the macrosatellite repeat causes autosomal dominant facioscapulohumeral muscular dystrophy (FSHD). [provided by RefSeq, Jun 2014]