A 27-year-old Caucasian woman began her third pregnancy after 3 injections of natalizumab. The patient decided to continue this treatment during the pregnancy. The baby (whose ethnic origin was Caucasian and black African), was born 2 weeks before the term. The weight was 3,140 g and the APGAR score at 10/10. Blood exams performed 12 days after birth revealed a mild pancytopenia with leucopenia, thrombocytopenia and anemia (Hb 9.3 g/dL, hematocrit 26%, blood platelets 126.000). Blood exams normalized at 3 months of age. Here, GSTM1 is linked to Thrombocytopenia.