Non-canonical member of the structural maintenance of chromosomes (SMC) protein family that plays a key role in epigenetic silencing by regulating chromatin architecture (By similarity). Promotes heterochromatin formation in both autosomes and chromosome X, probably by mediating the merge of chromatin compartments (By similarity). Plays a key role in chromosome X inactivation in females by promoting the spreading of heterochromatin (PubMed:23542155). Recruited to inactivated chromosome X by Xist RNA and acts by mediating the merge of chromatin compartments: promotes random chromatin interactions that span the boundaries of existing structures, leading to create a compartment-less architecture typical of inactivated chromosome X (By similarity). Required to facilitate Xist RNA spreading (By similarity). Also required for silencing of a subset of clustered autosomal loci in somatic cells, such as the DUX4 locus (PubMed:23143600). Has ATPase activity; may participate in structural manipulation of chromatin in an ATP-dependent manner as part of its role in gene expression regulation (PubMed:29748383). Also plays a role in DNA repair: localizes to sites of DNA double-strand breaks in response to DNA damage to promote the repair of DNA double-strand breaks (PubMed:25294876, PubMed:24790221). Acts by promoting non-homologous end joining (NHEJ) and inhibiting homologous recombination (HR) repair (PubMed:25294876). ATP + H2O = ADP + H(+) + phosphate Homodimer; homodimerizes via its SMC hinge domain (By similarity). Interacts with LRIF1 (PubMed:23542155). Recruited to inactivated chromosome X in females by Xist RNA (By similarity). Localizes at sites of DNA damage at double-strand breaks (DSBs) (PubMed:25294876, PubMed:24790221). Atypical member of the structural maintenance of chromosomes (SMC) protein family. Like other members of the SMC family, has ATPase activity, which is probably necessary for its engagement with chromatin, and a SMC hinge domain. However, the SMC hinge domain adopts an unconventional homodimeric arrangement augmented by an intermolecular coiled coil formed between the two monomers. This suggests that protein may assemble as a head-to-head parallel dimer without adopting a hairpin shape at the hinge domain, unlike the dimeric arrangement conventionally found in other members of the SMC protein family. The SMC hinge domain binds DNA and RNA. Sumoylated with SUMO1. The disease is caused by variants affecting the gene represented in this entry. SMCHD1 mutations lead to DUX4 expression in somatic tissues, including muscle cells, when an haplotype on chromosome 4 is permissive for DUX4 expression (PubMed:23143600). Ectopic expression of DUX4 in skeletal muscle activates the expression of stem cell and germline genes, and, when overexpressed in somatic cells, DUX4 can ultimately lead to cell death (PubMed:23143600). FSHD2 and FSHD1 share a common pathophysiological pathway in which the FSHD2 gene SMCHD1 can act as a modifier for disease severity in families affected by FSHD1 (PubMed:24075187, PubMed:25370034). The disease is caused by variants affecting the gene represented in this entry. Belongs to the SMC family. Highly divergent. Truncated N-terminus. Truncated N-terminus.