Rapsyn also known as RAPSN is a member of a family of proteins that are receptor associated proteins of the synapse. Rapsyn plays a crucial role in neuromuscular transmission. Rapsyn, or receptor-associated protein of the synapse, is primarily expressed in the postsynaptic membrane of skeletal muscle, where rapsyn is essential for the clustering of nicotinic acetylcholine receptors (nAChR). Rapsyn′s ability to self-associate through tetra-tricopeptide repeats facilitates interaction with the large intracellular domain of the nAChR α subunit, which is vital for proper localization and function of these receptors at the neuromuscular junction. Rapsyn not only modifies AChR trafficking within the cell but is also critical for agrin-induced AChR clustering, a process essential for functional synapse formation.