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. 2021 Aug 13;11(8):1469. doi: 10.3390/diagnostics11081469

Figure 1.

Figure 1

Schematic of FSHD-associated chromosome 4q D4Z4 regions analyzed by BSS (modified from [32]). The genomic regions assayed by the three most commonly used methods for FSHD diagnostics are shown. The methylation sensitive restriction enzyme (MSRE) digestion and Southern blotting method assays the methylation state of the most proximal FseI restriction enzyme site (yellow highlight) on both alleles for the 4q and 10q chromosomes when probed with p13E-11 [25,30]. The DR1 BSS assay identifies FSHD2-specific DNA hypomethylation [33]. The BSS assays used by Gaillard et al. separately amplify three different regions of the D4Z4 (BIS-5′, BIS-mid, BIS-3′; pink) that are also present on both alleles of the 4q and 10q chromosomes [34]. In contrast, the BSS assays used by Jones et al. amplify two products that are specific for the distal-most chromosome 4q, one for 4qA alleles (BSSA, blue), and the other for 4qA-L alleles (BSSL, orange), and one product upstream of the DUX4 ORF that is present on all four alleles (BSSX, green) [32]. The genomic region amplified by the BIS-3′ assay is completely within the BSSA amplified region and the DR1 region is completely within the BSSX region.