Figure 4. Facioscapulohumeral dystrophy type 1 (FSHD1) and facioscapulohumeral dystrophy type 2 (FSHD2), a disease continuum.
Patients with FSHD1 have a contraction of the D4Z4 repeat to a size of 1–10 repeat units (RU) (X-axis). Patients with FSHD2 show hypomethylation of the DR1 region in the presence of a normal sized D4Z4 repeat of 11–20 RU (Y axis). FSHD1+2 can be considered part of a FSHD disease continuum characterized by a contraction of the D4Z4 repeat (9–10 RU) and a hypomethylation status of the DR1 region because of mutations in D4Z4 chromatin modifiers.