Symptomatic Erythrocytosis Associated with a Compound Heterozygosity for Hb Lepore-Boston-Washington (δ87-β116) and Hb Johnstown [β109(G11)Val→Leu,GTG>TTG]

Abstract

Hb Johnstown [β109(G11)Val→Leu, GTG>TTG] has previously been described as a high oxygen affinity variant in a heterozygous state and in combination with β(0)-thalassemia (β(0)-thal). Because the variant does not separate from Hb A by routine methods it may be easily missed unless clinical suspicion is high. Hb Lepore-Boston-Washington (Hb LBW; δ87-β116) is a δβ hybrid variant that clinically manifests similarly to a β(+)-thal. Hb LBW is not detected by routine polymerase chain reaction (PCR) sequencing but is easily detected by electrophoretic methods. We describe a 19-year-old African American male with a compound heterozygosity for Hb Johnstown and Hb LBW. The patient presented with progressively worsening chest pains, headaches and erythrocytosis. He was repeatedly phlebotomized with symptomatic improvement and subsequently was confirmed to have the high oxygen affinity hemoglobin (Hb) variant. The lowest Hb and hematocrit (packed cell volume, PCV) achieved by phlebotomy was 16.1 g/dL and 0.51 L/L, respectively. Currently, he is no longer being phlebotomized, and is feeling relatively well except for minor chest pain. It is unclear to what degree the phlebotomies contributed to his subjective improvement. The combination of Hbs Johnstown and LBW has not been heretofore described, and in this case, was associated with marked symptomatic erythrocytosis. This unique combination results in a more pronounced phenotype, similar to or slightly more severe than, compound Hb Johnstown/β(0)-thal. This compound hemoglobinopathy will likely not be correctly classified using a single method of Hb detection and underscores the need for multiple characterization methods when indicated by the clinical picture.

Modelling the relationships between haemoglobin oxygen affinity and the oxygen cascade in humans

“…Interestingly, there are numerous reported cases worldwide of rare human Hb variants with permanently altered Hb binding affinity (Fairbanks et al 1971;Jones & Shih, 1980;Hoyer et al 1998;Oliveira et al 2010;Hoyer et al 2011;Inoue et al 2012;Szuberski et al 2012;Taliercio et al 2013;Collier et al 2016;Oliveira et al 2018). Specifically, genetic mutations in the variants' amino acid sequence of the alpha or beta Hb chains can phenotypically manifest as Hb with altered ODCs (P 50 ranging from Hb-Syracuse at 11 mmHg to Hb-Kansas at 48 mmHg).…”

Genotype–phenotype correlation of hereditary erythrocytosis mutations, a single center experience

“…The compound heterozygous Hb Johnstown/Lepore‐Boston‐Washington patient could have been misclassified as simple heterozygous Hb Johnstown if tested by DNA sequencing alone as the Hb Lepore delta/beta crossover event is not detected by many direct sequencing techniques of the HBB gene. This has clinical implications as the phenotype differs greatly from the two conditions, (Hgb 17.5 g/dL; MCV 87–104 fL) versus (21.4 g/dL; MCV 68.7 fL) . Finally, cases that illustrate the cost savings of an algorithmic approach include a 52 year‐old man that had been separately tested and found negative for JAK2 V617F, EPOR, EPAS1(HIF2A), EGLN1 (PHD2) , and VHL prior to ordering p50 and BPGM evaluation four months later.…”

“…After IRB approval, a review of our database and available clinical laboratory reports (from 1974 to present) identified 762 cases with positive identification of a clinically significant HOA Hb variant as classified in the HbVar online database or by our laboratory data . Alkaline/acid electrophoresis, isoelectric focusing (IEF), capillary electrophoresis (CE), high performance liquid chromatography (HPLC), mass spectrometry (MS) and Sanger sequencing of HBB , HBA1 , and HBA2 genes were variably performed according to our diagnostic protocols as required for definitive identification . Additionally (from 2011 to present) we evaluated 1192 patient samples submitted for test panels focused on hereditary erythrocytosis that includes p50 analysis, hemoglobin protein assays (HPLC, CE and MS) and Sanger sequencing of the clinically relevant gene regions associated with hereditary erythrocytosis [ EPOR (exon 8), EGLN1 (exons 1–5), EPAS1 (exon 9 and 12), VHL (exons 1–3), BPGM ].…”

“…Evaluation for hemoglobin (Hb) disorders has been a mainstay in our laboratory for over 40 years, during which we have used multiple methods for classification purposes. This has culminated in the identification of a large number of Hb variants . Those with altered oxygen affinity are of particular interest as approximately one third of the known HOAs are a known cause of hereditary erythrocytosis .…”

Diagnostic Strategies in Hemoglobinopathy Testing, the Role of a Reference Laboratory in the USA

“…These testing strategies allow effi-cient diagnoses of rare clinically significant hemoglobin disorders and decrease widespread indiscriminate testing that wastes resources. While continued suboptimal communication between clinical caregivers and laboratorians still result in missed opportu- nities to identify all clinically significant variants, the use of these testing strategies in our laboratory has facilitated the identification of rare and complex hemoglobin disorders from a wide variety of ethnic groups, including over 500 distinct named alpha, beta and gamma variants (of which 60+ were novel variants at the time of first detection), 99 beta thalassemia mutations and greater than 20 large deletional beta globin cluster deletion subtypes [4][5][6][7][8][9][10].…”