Facioscapulohumeral muscular dystrophy type 1 (FSHD1) is a progressive disorder that primarily affects the muscles of the face, shoulder blades (scapula), upper arms, and lower legs. The age of symptom onset is variable but typically occurs in the teenage years with more than half of individuals with FSHD1 having symptoms by age 20.

Individuals affected with FSHD1 have a 4q35 D4Z4 array that is contracted to a range of one to 10 repeat units (as opposed to 11 to 150 in individuals who are unaffected), associated strictly with the 4qA polymorphic allele. This test uses optical genome mapping (OGM) technology to detect the repeats of the D4Z4 regions at 4q35 in the presence of a 4qA allele. OGM also assesses the highly similar 10q26 D4Z4 region for internal interpretation purposes.

Clinical Support for OGM-Dx FSHD1 Testing

Bionano Laboratories offers unlimited clinical support to patients and providers through access to our genetic counselors who can discuss testing capabilities, strategy, informed consent, and results.

Providers can call our genetic counselors at


High-resolution analysis of the D4Z4 repeat array is performed using the Saphyr® genome imaging instrument. Ultra-high molecular weight DNA is extracted from whole blood using the Bionano Prep SP Blood and Cell Culture DNA Isolation Kit and labeled with the Bionano Prep DLS Labeling Kit. The labeled DNA is imaged in an array of nanochannels on the Saphyr platform. The molecules aligning to regions of interest are extracted and assembled. The resulting consensus maps are used for the Bionano EnFocus™ FSHD1 analysis. The D4Z4 repeat regions in chromosomes 4 and 10 are sized and the permissive and non-permissive haplotypes (4qA and 4qB) assigned. The method cannot detect single nucleotide variants that do not impact sequence motif sites and may miss small variants with potential functional impacts.

What is optical genome mapping?

Optical genome mapping is a single process capable of detecting all classes of genetic structural variation. This includes deletions, duplications, insertions, translocations, inversions, and repeat contractions and expansions. This technology relies on the direct imaging of ultra-high molecular weight DNA molecules. Using direct label and stain technology, fluorescent labels are attached to a 6 bp sequence motif, occurring 20 times per 100 kbp. Fluorescent labels are attached nondestructively and leave the DNA samples intact. The labeled DNA is linearized through nanochannels and imaged creating a genomic map. Learn more about OGM data services.

Can this test diagnose both FSHD1 and FSHD2?

No, this test only assesses genetic changes associated with FSHD1.

What if this test is negative?

If this test is non-diagnostic, a more comprehensive genetic evaluation might be warranted. This may include whole exome sequencing using the NextStepDx PLUS test, which evaluates the coding regions of all 20,000+ genes in the genome.