No patients with MIS-C who did not receive IVIG had IgG autoantibodies against most of the previously reported proteins including ANX11, ATP4A, ECE1, FAM84A, NAPB, TROVE2 (Ro60), PDLIM5, and UBE3A, and none had IgA autoantibodies against FAM84A and TNNC2 with one exception. This evidence concerns the gene ATP4A and COVID-19–associated multisystem inflammatory syndrome in children.