Abstract Background Unstable hemoglobinopathies are rare inherited disorders of hemoglobin causing a reduction of hemoglobin molecule solubility. This results in an unstable hemoglobin tetramer/globin polypeptide, which precipitates within the red blood cell. Affected red blood cells have a reduced lifespan due to oxidative stress and cellular rigidity, and tend to be phagocytized by spleen macrophages more rapidly. Unstable hemoglobin is frequently under- or misdiagnosed, because its clinical presentation varies broadly. Therefore, testing for unstable hemoglobinopathies is indicated in cases of unexplained hemolytic anemia. However, this approach is not systematically followed in clinical practice. Case report A 25-year-old Caucasian man with a recent history of a presumed viral upper respiratory infection was referred to the hematology outpatient clinic because of hemolytic anemia. The patient had scleral icterus, moderate splenomegaly, and mild macrocytic anemia with high reticulocyte count. Unconjugated bilirubin and lactate dehydrogenase were elevated. Haptoglobin was undetectable. Direct antiglobulin test was negative. Blood smear examination revealed anisopoikilocytosis, polychromasia, bite cells, and basophilic stippling, but no Heinz bodies. High-performance liquid chromatography and capillary electrophoresis showed slightly increased hemoglobin A2, normal fetal hemoglobin, and a variant hemoglobin. Deoxyribonucleic Acid sequencing revealed the heterozygous mutation c430delC in the beta-globin gene hallmark of hemoglobin Montreal II and the heterozygous mutation c287C>T in the alpha-globin gene corresponding to hemoglobin G-Georgia, indicative of the not yet described combination of double-heterozygous hemoglobin Montreal II and hemoglobin G-Georgia variants. Hemoglobinopathy Montreal II was here not associated with β-thalassemia syndrome, and carriers did not show ineffective erythropoiesis. In addition to the case report, we provide information about the largest pedigree with hemoglobinopathy Montreal II identified to date. Conclusion We emphasize that a transitory acute condition may uncover an underlying inherited red blood cell disorder. In this regard, awareness should be raised among hematologists caring for adult patients that unstable hemoglobinopathies should be considered in the differential diagnosis of unexplained hemolytic anemias.
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