Abstract Details

Title DNA Combing Assay for Detection of Contraction-Dependent Facioscapulohumeral Muscular Dystrophy (FSHD1)

Topic Muscle Disease/Neuromuscular Junction

Presentation(s) (-)

Poster/Presentation
Number 005

Objective

Background FSHD is an autosomal dominant disorder with a prevalence of 4-10 per 100,000 and is associated with contraction of the D4Z4 region (3.3 kb repeat motif that contains DUX4, double homeobox 4, gene) at the subtelomeric region of 4q35. Affected alleles have 1- 10 copies of D4Z4 on the 4qA allele, while unaffected alleles have 11-100 copies. Contractions of the partner 4qB allele or a homologous region on chromosome 10q26 are non-pathogenic. Previously, detection of truncated D4Z4 has been based on Southern blot (SB) analysis. SB analysis can only provide a size approximation, yields ambiguous results in at least 20% of cases and, as we show in this study, can miss affected mosaic individuals. DNA combing provides an attractive alternative method for the diagnosis of contracted alleles in FSHD. In this technology, individual DNA fibers are visualized and measured, allowing differentiation between A and B alleles and 4q and 10q alleles, accurate sizing of all alleles and identification of mosaic affected individuals.

Design/Methods DNA was combed from agarose plugs supplied by Athena Diagnsotics.

Results The validation series consisted of combed DNA from 2 cell lines and from leukocyte plugs from 35 individuals submitted to Athena Diagnostics for SB. The samples were blinded to laboratory personnel performing the analysis. The was 100% concordance in the 7 samples determined to affected by SB analysis and the 2 cell lines. One of the 28 samples determined to be unaffected by SB analysis was demonstrated to be a mosaic individual with 2 normal sized alleles and a contracted affected allele.

Conclusions We successfully validated molecular combing for the diagnosis of FSHD in a commercial laboratory representing an improvement from the currently available methods in the US.

Authors/Disclosures
Charles Strom, MD, PhD (Quest Diagnostics Nichols Institute) PRESENTER	No disclosure on file
Chris M. Kozma	No disclosure on file
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