Based on the fact that SMCHD1 mutations are associated with D4Z4 DNA hypomethylation leading to FSHD2 and to increased severity of FSHD1, SMCHD1 gene correction with CRISPR-Cas9 was performed in primary and immortalized muscle cells from one FSHD patient. The gene discussed is SMCHD1; the disease is facioscapulohumeral muscular dystrophy.