The LDL receptor-related protein 4 (LRP4), a member of the LDL receptor family, plays a critical role in synaptic development and maintenance, particularly at the neuromuscular junction (NMJ). It interacts with agrin, a motor neuron-derived protein, to activate muscle-specific kinase (MuSK), facilitating the clustering of acetylcholine receptors (AChRs) essential for neuromuscular signal transmission. Autoantibodies targeting LRP4 are implicated in autoimmune disorders, most notably myasthenia gravis (MG), a condition characterized by muscle weakness and fatigue. In approximately 1-5% of MG patients, LRP4 antibodies are detected, often in cases lacking antibodies against AChR or MuSK, defining a distinct serological subgroup. These antibodies disrupt LRP4’s function, impairing agrin-MuSK signaling and AChR organization. Beyond MG, LRP4 autoimmunity has been linked to other conditions like amyotrophic lateral sclerosis (ALS) and neuromyelitis optica spectrum disorders (NMOSD), though evidence remains preliminary. LRP4 is also expressed in non-neural tissues, such as bone and kidney, suggesting broader physiological roles. Research into LRP4 antibodies aids in diagnostics (via cell-based assays) and understanding disease mechanisms, potentially guiding targeted immunotherapies. Its dual role in health and disease underscores LRP4 as a key molecule in neuroimmunology and translational research.