A tale of two variants: The first reported case of hemoglobin Rush and hemoglobin S in a compound heterozygote.

Hemoglobinopathies are among the most common inherited disorders worldwide, caused by various mutations in the hemoglobin (Hb) genes. These mutations can lead to different clinical outcomes, some of which cause significant symptoms, highlighting their importance in global health and genetic research. In this context, this case report details the first known instance of compound heterozygosity for Hb Rush (HBB:c.304G > C) and Hb S (HBB:c.20A > T), emphasizing the diagnostic challenges posed by rare Hb variants, particularly those that mimic Hb S. Specifically, a 14-year-old male patient was referred due to mild anemia, microcytosis, and hemolysis, with a suspicion of sickle cell disease (SCD). However, hematological, biochemical, chromatographic, and electrophoretic analyses were inconsistent with SCD, prompting further molecular investigations. High-performance liquid chromatography identified a hemoglobin variant with a retention time overlapping Hb S. Additionally, alkaline electrophoresis revealed hybrid tetramers typical of unstable Hbs, such as Hb Rush. These laboratory findings were further confirmed through Sanger sequencing of the HBB gene, which demonstrated heterozygosity for both Hb Rush and Hb S, establishing a rare genotype that has not been previously reported. The thermal instability and structural changes involving the G3 (101) glutamate-to-glutamine substitution in Hb Rush account for the hematological phenotype observed in this patient. Therefore, in cases like this one, it is crucial to combine various laboratory methodologies-such as electrophoresis and molecular analysis-with the patient's clinical information. This comprehensive approach enables a critical interpretation of potential genotypes, ensuring accurate diagnosis, appropriate clinical follow-up, and treatment.