Background/Case Studies: The Er blood group system consists of five known Er antigens (Era, Erb, Er3, Er4 and Er5). The system is defined by missense mutations in the gene PIEZO1, which codes for a mechanosensory ion channel that serves as the carrier molecule for the Er blood group antigens. Except for Erb, the known antigens of the Er group are high-prevalence antigens. Er3, Er4 (also known as ERSA) and Er5 (also known as ERAMA) have been previously implicated in hemolytic disease of the fetus and newborn (HDFN).
Study
Design/Methods: Case Study.
Results/Findings: In November of 2024, a 31-year-old Native American woman with a twin pregnancy presented to OU Health Partners Inc., for a prenatal checkup and was found to have a positive antibody screen. She had six prior uneventful pregnancies and no history of transfusions. The antibody was initially thought to be anti-Kell but later recognized to be a rare antibody to a high prevalence antigen. A month later, she was admitted to OU Children’s Hospital at 32 weeks and 5 days gestation for continuous fetal monitoring. She had an elevated middle cerebral artery (MCA) doppler ultrasound assessment , gestational diabetes, intrahepatic cholestasis of pregnancy and fetal malpresentation. Due to her high-risk pregnancy and planned Cesarean section, there was concern among the clinical team that she would need a transfusion. The antibody had yet to be identified so her blood sample was sent to the New York Blood Center for further analysis. Meanwhile, the blood bank attempted to identify “least incompatible” blood products. Five days later, her MCA doppler values continued to elevate so the team performed a C-section. The neonates were delivered at 33 weeks and 3 days gestational age. The patient had a postpartum hemorrhage and was treated with carboprost tromethamine and misoprostol. Her hemoglobin trended downwards from 12.3 g/dL to 8.6 g/dL but remained stable thereafter. She did not require a transfusion and was discharged two days after delivery. The neonates were admitted to the NICU for prematurity and had laboratory evidence of mild hemolysis. One of the neonates required phototherapy due to a bilirubin level of 10.8 g/dL. Neither neonate required a transfusion, and they were discharged a month after delivery. The maternal antibody was eventually identified as an alloantibody to Er4. Conclusions: There are previously reported cases of Er4 alloantibodies during pregnancy that resulted in severe HDFN. This case, fortunately, demonstrated a different outcome. However, this case highlights the need for further research regarding the Er blood group system and the possible consideration of a registry of blood donors with alloantibodies to Er antigens.
