Non-canonical member of the structural maintenance of chromosomes (SMC) protein family that plays a key role in epigenetic silencing by regulating chromatin architecture (PubMed:26091879, PubMed:29887375). Promotes heterochromatin formation in both autosomes and chromosome X, probably by mediating the merge of chromatin compartments (PubMed:23754746, PubMed:23819640, PubMed:26391951, PubMed:28587678, PubMed:29887375). Plays a key role in chromosome X inactivation in females by promoting the spreading of heterochromatin (PubMed:18425126, PubMed:22841499, PubMed:26391951, PubMed:29887375). 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 (PubMed:29887375). Required to facilitate Xist RNA spreading (PubMed:29887375). Also required for silencing of a subset of clustered autosomal loci in somatic cells, such as the DUX4 locus (PubMed:23754746, PubMed:23819640, PubMed:28587678). 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:26391951, PubMed:27059856). 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 (By similarity). Acts by promoting non-homologous end joining (NHEJ) and inhibiting homologous recombination (HR) repair (By similarity). Required during preimplantation development, probably acts by regulating chromatin architecture (PubMed:29900695). ATP + H2O = ADP + H(+) + phosphate Homodimer; homodimerizes via its SMC hinge domain (PubMed:26391951, PubMed:26733688, PubMed:27059856). Interacts with LRIF1 (PubMed:26391951). Recruited to inactivated chromosome X in females by Xist RNA (PubMed:29887375). Localizes at sites of DNA damage at double-strand breaks (DSBs) (By similarity). During embryogenesis, specifically expressed in immature olfactory sensory neurons. Expressed in the nasal placodes and optic vesicles at day 9.5 dpc and in the nasal epithelium at 12.5 dpc (PubMed:28067911). Expressed in the nasal cavity in 14.5 dpc animals (PubMed:28067911). Expression is repressed by CDX2. Atypical member of the structural maintenance of chromosomes (SMC) protein family (PubMed:26733688, PubMed:27059856). Like other members of the SMC family, has ATPase activity, which is probably necessary for its engagement with chromatin, and a SMC hinge domain (PubMed:26733688, PubMed:27059856). 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 (PubMed:26733688). The SMC hinge domain binds DNA and RNA (PubMed:26091879). Sumoylated with SUMO1. Defects in Smchd1 are the cause of the MommeD1 (modifier of murine metastable epialleles) phenotype, a semi-dominant suppressor of variegation (PubMed:18425126, PubMed:21553025). Mice display female-specific mid-gestation lethality and hypomethylation of the X-linked gene Hprt1, due to defects in X inactivation (PubMed:18425126, PubMed:21553025, PubMed:23754746). Mice do not show defects on telomeres length (PubMed:18425126, PubMed:21553025). Male mice are less affected, with some surviving to become fertile adults on the FVB/n genetic background (PubMed:18425126). On other genetic backgrounds, all males lacking die perinatally (PubMed:18425126). A subset of clustered autosomal loci display hypomethylation and derepression (PubMed:23754746, PubMed:23819640, PubMed:28587678). Belongs to the SMC family. Highly divergent. Truncated N-terminus.