0.56% of CMS patients have mutations in LRP4. 1–2% of MG patients have Lrp4 autoantibodies. MuSK autoantibodies inhibit MuSK‐Lrp4 interaction, obstructing normal trophic signalling at the NMJ and induce myasthenia. Here, LRP4 is linked to congenital myasthenic syndrome.