TRIM21 and Thrombocytopenia: Her condition was serious and could not be improved by conventional treatment; however, she responded well to exchange transfusion therapy.<h4>Case presentation</h4>A female infant, aged 1 month and 3 days, was admitted to the Children's Hospital of Soochow University owing to the "discovery of thrombocytopenia over 1 month." She tested positive for anti-SSA IgG, anti-Ro-52 IgG, and anti-mitochondrial M2 antibodies.