An Unusual Presentation of Erythrocytosis Resulting in the Identification of a Novel Unstable Hemoglobin Variant: Hb Koskullskulle HBB: C.311T > C (p.Phe104Ser).

Elevated hemoglobin (Hb) concentration, erythrocytosis, is a common phenomenon that can be caused by primary or secondary underlying conditions. In this report, we describe a previously unknown mutation in the β globin gene resulting in high Hb concentrations combined with elevated reticulocytes in two family members spanning two generations. In the index patient the variant was first noted during HbA1c monitoring. While both ion-exchange chromatograms used for HbA1c analysis and isoelectric focusing indicated the presence of a β globin variant, the chromatographic method used for hemoglobinopathy screening mostly failed to detect the variant. Mass spectrometry demonstrated a -60 Da β globin variant and Sanger sequencing revealed a previously unknown p.Phe104Ser substitution in the HBB gene [HBB:c.311T > C]. This mutation affects the interaction with heme and results in increased oxygen affinity as well as instability. Common causes of acquired as well as congenital erythrocytosis were ruled out. This novel variant was named Hb Koskullskulle (IthaID 4114) from the place of origin of the family in which it was found.