This gene is located within a D4Z4 repeat array in the subtelomeric region of chromosome 4q. The D4Z4 repeat is polymorphic in length; a similar D4Z4 repeat array has been identified on chromosome 10. Each D4Z4 repeat unit has an open reading frame (named DUX4) that contains two homeoboxes; the repeat-array and ORF is conserved in other mammals. There was no evidence for transcription from standard cDNA libraries however RTPCR and in-vitro expression experiments indicate that the ORF is transcribed and the encoded protein has been reported to function as a transcriptional activator of paired-like homeodomain transcription factor 1 (PITX1; GeneID 5307). Contraction of the microsatellite repeat causes autosomal dominant facioscapulohumeral muscular dystrophy (FSHD).