Non-Immune Hemolytic Anemia of Pregnancy: Heterozygous RBC Variants Elude Diagnosis

A 25 year old G3P2002 El Salvadorean female, with a prior history of pregnancy related anemia of unknown etiology, presented at 24 weeks gestation with symptomatic anemia (hemoglobin 2.9 g/dL) including dizziness, weakness and fatigue and no active signs of bleeding. Blood work included normal range results for LDH, haptoglobin, indirect and direct Coombs indicating no intravascular or immune driven hemolysis. Peripheral smear showed spherocytosis and stomatocytosis, concerning for an intrinsic RBC defect. Other workup included hemoglobin electrophoresis with slight increase in Hb A2 of 3.3%, flow cytometry negative for a lymphoproliferative disorder or paroxysmal nocturnal hemoglobinuria, no evidence of G6PD deficiency, and a bone marrow biopsy negative for marrow dysplasia, aplasia or HLH. Abdominal ultrasound revealed hypersplenism. The anemia was attributed to a non-immune hemolytic anemia with extra corpuscular RBC destruction in the spleen but without evidence of RBC destruction in the bone marrow or peripheral blood.

After a prolonged 10-week hospitalization, the patient received a trial of steroids, 8 IV immunoglobulin infusions with minimal benefit, and total of 22 units of packed red blood cells. She underwent an elective induction and delivery at 34 weeks of pregnancy. During the postpartum period, she continued to have persistent anemia. A partial splenic embolization was attempted, complicated by splenic abscesses resulting in a splenectomy. Post splenectomy, the patient's hemoglobin and hematocrit stabilized to 11.7/37.8 at her three week outpatient visit.

Molecular testing for Next Generation Sequencing (NGS) with Laboratory Hereditary Hemolytic Anemia Comprehensive Panel was also performed, revealing four different heterozygous variants. While these mutations individually have not been proven to cause hemolysis, the four alterations together, with the stressor of pregnancy, likely induced a non-immune hemolytic anemia.

Non-immune hemolytic anemia is caused by intracorpuscular defects within the red blood cells or extracorpscular by environmental factors. The patient was found with four heterozygous variants in HK1, RPS19, SPTA1 and HBB, implicated in intracorpuscular defects. The HK1 gene, expressed in erythrocytes, encodes hexokinase, and provides red blood cells ATP. HK deficiency is a rare hereditary disorder associated with mild to severe non-spherocytic hemolytic anemia. The RPS19 gene encodes for a ribosomal protein involved in erythropoiesis. Clinically significant mutations in this gene cause Diamond Blackfan anemia. The SPTA1 gene encodes alpha spectrin subunits, which are a part of red cell membrane cytoskeleton and maintains its shape. Mutations in this gene have been implicated in hereditary spherocytosis. One case report described severe non-immune hemolytic anemia in a neonate with hereditary spherocytosis secondary a heterozygous mutation of the SPTA1 gene. Lastly, the HBB gene encodes for hemoglobin beta globin chains where alterations have been associated with hemolytic anemia, sickle cell anemia, and beta thalassemia. Several case reports described heterozygous variants of HBB and association with hemoglobin instability and extravascular hemolysis.

Heterozygous mutations in the above genes have been rarely reported in literature to cause non-immune hemolytic anemia. Although unclear, pregnancy appeared to be the inciting factor in our patient with these mutational variants that have a potential role in extravascular hemolysis. While there have been few case reports describing autoimmune hemolytic anemia caused by pregnancy, a non-immune hemolytic anemia from 4 heterozygous variants in RBC genes, as seen in our patient, has not been previously described.