TMEM53 is a nuclear envelope transmembrane protein with dual roles in bone homeostasis and viral restriction. Functionally, TMEM53 negatively regulates bone morphogenetic protein (BMP) signaling by blocking the cytoplasm-nucleus translocation of phosphorylated SMAD1/5/9 proteins in osteoblast lineage cells, thereby suppressing osteogenesis 1. This regulatory mechanism involves TMEM53's transmembrane domain, which is essential for its molecular interactions 2. Beyond skeletal biology, TMEM53 functions as a novel intrinsic antiviral factor against swine acute diarrhea syndrome coronavirus (SADS-CoV), where it interacts with viral non-structural protein 12 to disrupt RNA-dependent RNA polymerase assembly and viral replication independently of interferon signaling 2. Biallelic loss-of-function TMEM53 variants cause craniotubular dysplasia, Ikegawa type (CTDI), an autosomal recessive sclerosing bone disorder characterized by dysregulated BMP-SMAD signaling and accelerated bone formation 1. Clinical manifestations include calvarial thickening, skeletal modeling abnormalities, and notably, progressive childhood blindness due to optic canal narrowing 34. Pathogenic variants include nonsense mutations, deletions affecting splice sites, and novel missense mutations that introduce ubiquitination sites triggering protein degradation 5. TMEM53 also regulates cell cycle progression through p53-dependent pathways, influencing stress-induced senescence 6.