Table 1.

Summary of Molecular Genetic Testing Used in Facioscapulohumeral Muscular Dystrophy

DisorderGene 1/LocusTest MethodMutation Detected 2Mutation Detection Frequency 3
FSHD1D4Z4Targeted mutation analysisContraction mutation of number of D4Z4 repeats95%
Haplotype analysisAnalysis to confirm that the D4Z4 contraction mutation occurred on a permissive haplotype 4Not applicable
FSHD2D4Z4Methylation analysisD4Z4 hypomethylation (<25% methylation)<5%
SMCHD1Sequence analysis 5SMCHD1 sequence variants<5%

See Molecular Genetics for information on allelic variants.


The ability of the test method used to detect a mutation that is present in the indicated gene/locus


4A161 is most common permissive haplotype, but others are reported (4A159, 4A168, 4A166H) [Lemmers et al 2010a]. All individuals with FSHD carry a permissive haplotype. Because 66% of controls also carry a permissive haplotype, this analysis (without sizing of the repeat array) is often not informative.


Examples of mutations detected by sequence analysis may include small intragenic deletions/insertions and missense, nonsense, and splice site mutations; typically, exonic or whole-gene deletions/duplications are not detected. For issues to consider in interpretation of sequence analysis results, click here.

From: Facioscapulohumeral Muscular Dystrophy

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