NMD (Nonsense-Mediated mRNA Decay) is an intracellular quality control mechanism responsible for identifying and degrading mRNAs containing nonsense codons, preventing the synthesis of abnormal proteins. NMD relies on a series of proteins, including UPF1, UPF2, and UPF3, which work together in the nucleus and cytoplasm to recognize aberrant mRNAs and promote their degradation. NMD is involved in the precise regulation of genetic information and various biological processes and signaling pathways. Specific gene expression and mutations can affect the efficiency of the NMD pathway, associated with the development of various genetic diseases.