Facioscapulohumeral muscular dystrophy:  consequences of chromatin relaxation.
OBJECTIVE
In recent years, we have seen remarkable progress in our understanding of the disease mechanism underlying facioscapulohumeral muscular dystrophy (FSHD). The purpose of this review is to provide a comprehensive overview of our current understanding of the disease mechanism and to discuss the observations supporting the possibility of a developmental defect in this disorder.


RESULTS
In the majority of cases, FSHD is caused by contraction of the D4Z4 repeat array (FSHD1). This results in local chromatin relaxation and stable expression of the DUX4 retrogene in skeletal muscle, but only when a polymorphic DUX4 polyadenylation signal is present. In some cases (FSHD2), D4Z4 chromatin relaxation and stable DUX4 expression occur in the absence of D4Z4 array contraction. DUX4 is a germline transcription factor and its expression in skeletal muscle leads to activation of early stem cell and germline programs and transcriptional activation of retroelements.


CONCLUSIONS
Recent studies have provided a plausible disease mechanism for FSHD in which FSHD results from inappropriate expression of the germline transcription factor DUX4. The genes regulated by DUX4 suggest several mechanisms of muscle damage, and provide potential biomarkers and therapeutic targets that should be investigated in future studies.
Department of Human Genetics, Leiden University Medical Center, Leiden, Netherlands. Maarel@lumc.nl
Silvère M
SM
van der Maarel
Daniel G
DG
Miller
Rabi
R
Tawil
Galina N
GN
Filippova
Stephen J
SJ
Tapscott
D000818:Animals; D002843:Chromatin / Q000473:pathology*; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology; D020391:Muscular Dystrophy, Facioscapulohumeral / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology; D014158:Transcription, Genetic
D002843:Chromatin; C121257:DUX4L1 protein, human; D018398:Homeodomain Proteins