Neonatal Alloimmune Thrombocytopenia with HLA and HPA-3a Antibodies in a Down Syndrome Neonate

Abstract Introduction/Objective Neonatal Alloimmune Thrombocytopenia (NAIT) is a rare cause of thrombocytopenia seen in 1 in 11,000 neonates with lethal risks such as intracranial hemorrhage. This is caused by maternal antibodies against fetal platelets and the most common culprits are antibodies to Human Platelet Antigen-1b (HPA-1b) but rarely to Human Leukocyte Antigen (HLA) antibodies. We describe a rare case of a newborn with Down syndrome with maternal antibodies against HLA and presumed antibodies against HPA-3a. Down syndrome causes hematologic abnormalities with mild thrombocytopenia. Methods/Case Report A preterm male with Down syndrome was born via Cesarean delivery due to non-reassuring fetal heart tracing at a gestational age of 35 weeks. He was admitted for low birth weight and his hospital course was complicated by severe thrombocytopenia of 37 x 10^9/L without bleeding symptoms. Initially attributed to his trisomy 21 but due to his suboptimal response to platelet transfusion, NAIT was suspected. The mother had antibodies against HLA on initial screen and was presumed to have HPA-3a antibodies since she was homozygous for HPA-3b antigen. The neonate was managed with multiple transfusions of platelets and Intravenous Immunoglobulin (IVIG). The platelet count stabilized to 325 x 10^9/L on his 25th day of life. Results (if a Case Study enter NA) n/a Conclusion To our knowledge, this is the only published case of NAIT with both HPA-3a and HLA antibodies in a Down syndrome neonate. It is unclear whether the primary reason for thrombocytopenia is due to NAIT caused by HPA-3a antibodies or HLA antibodies or his existing Down syndrome. This case contributes to understanding the complexity between immune-related diseases such as NAIT and genetic conditions such as Down syndrome. Although NAIT occurs rarely, timely diagnosis and treatment is of utmost importance to prevent lethal complications.