Facioscapulohumeral muscular dystrophy

DNA diagnosis

DNA diagnosis in FHSD is based on sizing of the D4Z4 repeat array on chromosome 4. DNA is digested by EcoRI, a combination of EcoRI and BlnI, and by XapI, respectively. After digestion, the DNA is separated in adjacent lanes by pulsed field gel electrophoresis, which allows the separation of the repeat arrays on chromosomes 4 and 10. Next, the DNA is transferred to a nylon membrane and hybridized with probe p13E-11. This probe recognizes the region just proximal to the D4Z4 repeat array and the homologous repeat array on chromosome 10 and is contained within the EcoRI restriction fragment. The repetitve nature of the D4Z4 repeat does not allow the use of the repeat unit itself as a probe.

After hybridization, four fragments can be identified in the EcoRI lane: two from chromosome 4 and two from chromosome 10. To assign these fragments to their respective chromosome ends, BlnI and XapI can be used. While repeat units from chromosome 4 are resistant to the restriction enzyme BlnI, units from chromosome 10 are resistant to XapI. Thus, upon EcoRI/BlnI restriction, two fragments will disappear in comparison to the EcoRI lane and can generally be assigned to chromosome 10. Analagous to BlnI, two fragments will disappear in the XapI lane and can generally be assigned to chromosome 10. Fragments <38kb and resistant to BlnI (and sensitive for XapI) are associated with FSHD.

DNA diagnosis for FSHD is routinely performed in our department. Standard diagnosis is mostly performed by linear gel electrophoresis allowing precise sizing of the disease allele. For more information please contact: Bert Bakker, Ph.D. E-mail: e.bakker@lumc.nl or Silvère van der Maarel, Ph.D. E-mail: maarel@lumc.nl)