Immune thrombocytopenia with antiphospholipid antibodies in monozygotic twins

We describe monozygotic twins with immune thrombocytopenia (ITP) associated to antiphospholipid antibodies with a dissimilar clinical expression. The first patient was diagnosed to have ITP at 63 years old and was treated with corticosteroids. She presented ulterior exacerbations of thrombocytopenia requiring intravenous immunoglobulin and subsequent treatment with rituximab. She ultimately had a favorable response without thrombotic events during follow-up. The second patient who had a history of three spontaneous abortions and endometrial adenocarcinoma in complete remission was evaluated for severe thrombocytopenia, ITP was diagnosed at the age of 63. She was treated with steroids and had a favorable response. After few months she developed deep venous thrombosis and pulmonary embolism requiring anticoagulation therapy without hemorrhagic events. Both patients were found to have antiphospholipid antibodies and HLA DR4 (DRB1*04) and HLA DR5 (DRB1*12). The association of those two entities in monozygotic twins could support the presence of common predisposing genes. However, with both patients being genotipically identical, the clinical expression was different. Those cases highlight the possibility that environmental factors may affect the expression of those disorders.