title: A focal domain of extreme demethylation within D4Z4 in FSHD2.
abstract: OBJECTIVE
  Facioscapulohumeral muscular dystrophy (FSHD) is a neuromuscular disease with an unclear genetic mechanism. Most patients have a contraction of the D4Z4 macrosatellite repeat array at 4qter, which is thought to cause partial demethylation (FSHD1) of the contracted allele. Demethylation has been surveyed at 3 restriction enzyme sites in the first repeat and only a single site across the entire array, and current models postulate that a generalized D4Z4 chromatin alteration causes FSHD. The background of normal alleles has confounded the study of epigenetic alterations; however, rare patients (FSHD2) have a form of the disease in which demethylation is global, i.e., on all D4Z4 elements throughout the genome. Our objective was to take advantage of the global nature of FSHD2 to identify where disease-relevant methylation changes occur within D4Z4.
  
  
  METHODS
  Using bisulfite sequencing of DNA from blood and myoblast cells, methylation levels at 74 CpG sites across 3 disparate regions within D4Z4 were measured in FSHD2 patients and controls.
  
  
  RESULTS
  We found that rates of demethylation caused by FSHD2 are not consistent across D4Z4. We identified a focal region of extreme demethylation within a 5' domain, which we named DR1. Other D4Z4 regions, including the DUX4 ORF, were hypomethylated but to a much lesser extent.
  
  
  CONCLUSIONS
  These data challenge the simple view that FSHD is caused by a broad "opening" of D4Z4 and lead us to postulate that the region of focal demethylation is the site of action of the key D4Z4 chromatin regulatory factors that go awry in FSHD.
authors.affiliation: Department of Pediatrics and Lillehei Heart Institute, Minneapolis, MN, USA.
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Hartweck
authors.forename: Lindsey J
authors.initials: LJ
authors.lastname: Anderson
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lemmers
authors.forename: Abhijit
authors.initials: A
authors.lastname: Dandapat
authors.forename: Erik A
authors.initials: EA
authors.lastname: Toso
authors.forename: Joline C
authors.initials: JC
authors.lastname: Dalton
authors.forename: Rabi
authors.initials: R
authors.lastname: Tawil
authors.forename: John W
authors.initials: JW
authors.lastname: Day
authors.forename: Silvère M
authors.initials: SM
authors.lastname: van der Maarel
authors.forename: Michael
authors.initials: M
authors.lastname: Kyba
mesh_terms: D002843:Chromatin / Q000235:genetics*; D002879:Chromosomes, Human, Pair 10; D002894:Chromosomes, Human, Pair 4; D018899:CpG Islands / Q000235:genetics*; D019175:DNA Methylation / Q000235:genetics*; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D020391:Muscular Dystrophy, Facioscapulohumeral / Q000235:genetics*; D032446:Myoblasts / Q000502:physiology*; D010641:Phenotype; D015183:Restriction Mapping
chemical_list: D002843:Chromatin; C121257:DUX4L1 protein, human; D018398:Homeodomain Proteins