Thrombotic events in compound heterozygotes for a high affinity hemoglobin variant: Hb Milledgeville [alpha44(CE2)Pro-->Leu (alpha2)] and factor V Leiden

High-Oxygen-Affinity Hemoglobins-Case Series and Review of the Literature

Modifications of the hemoglobin (Hb) structure in regions involving the regulation of oxygen transport may lead to an increased oxygen affinity for the hemoglobin molecule and impaired oxygen delivery to the tissues. Herein, we present six patients with high-oxygen-affinity Hb variants, either in heterozygous form or in compound heterozygosity (such as heterozygosity for Hb Hiroshima, Köln, Crete, and compound heterozygosity Hb Crete with β or δβ thalassemia), in order to demonstrate the need for prompt and accurate diagnosis and enrich the limited literature due to the rarity of such cases. Hb Crete, Hb Hiroshima, and Hb Köln have distinct pathophysiologies and may result in different clinical phenotypes. In conclusion, high-oxygen-affinity hemoglobins are rare and inherited within a dominant autosomal manner, have various clinical presentations, and should always be suspected in patients with erythrocytosis. Their management (as phlebotomy or low-dose aspirin) should be based on an individualized assessment of the risk of complications, the medical history, concomitant symptoms, and quality of life.

First Report of an α Chain Variant [Hb Coombe Park (HBA2: c.382A>G)] from India, Coinherited with a Novel SERPINC1 Gene Mutation: A Double Whammy?

Coinheritance of a high oxygen affinity structural hemoglobin (Hb) variant along with a thrombophilia marker is a rare occurrence. This may lead to a multi fold increase in the risk of thrombosis in patients. We report here a first case of Hb Coombe Park (HBA2: c.382A>G; p.Lys128Glu) from India, coinherited with a novel mutation (c.839C>G; p.Ser280Ter) on the SERPINC1 gene. This coinheritance has not been reported before. Though the patient is presently asymptomatic, identification of these variants will help in genetic counseling and to decide the future course of action in case of any clinical complications.

High-oxygen-affinity hemoglobinopathy-associated erythrocytosis: Clinical outcomes and impact of therapy in 41 cases

We describe presenting features, treatment strategies, and follow-up events involving 41 patients (median age 39 years, range 1-81; 54% males) with high oxygen affinity (HOA) hemoglobinopathy-associated erythrocytosis, seen at our institution (1973-2020). Thirty-four (83%) patients carried β-chain (13 Malmo, 4 Olympia, 3 San Diego, 2 Wood) and 7 (17%) α-chain (4 Dallas and one each Columbia-Missouri, Jackson, and Wayne) variants. Median (range) hemoglobin (Hgb)/hematocrit (Hct), serum erythropoietin and p50 were 18 g/dL/52.9% (16-21.9/48-66), 10.4 mIU (4-36.3), and 20 mmHg (12-25), respectively. Family history was documented in 24 patients and history of thrombosis in two (5%). Treatment included phlebotomy in 23 and antiplatelet therapy in 21 patients. At a median follow-up of 10 years, 23 (56%) patients reported one or more symptoms that were thought to be related to their increased Hct while thrombosis was documented in 10 (24%) patients. Neither Hgb/Hct level nor active phlebotomy showed a significant correlation with either thrombotic or nonthrombotic symptoms (p > .1 in all instances). Among 23 pregnancies recorded, 78% resulted in live births and no fetal loss was attributed to erythrocytosis. The current study does not implicate Hgb/Hct level as a major contributor of morbidity in HOA hemoglobinopathy-associated erythrocytosis and suggests limited therapeutic value for phlebotomy.

How we diagnose and manage altered oxygen affinity hemoglobin variants

Altered oxygen affinity variant hemoglobins (Hbs) are caused by mutations of the globin genes. Changes in Hb oxygen affinity shift the oxygen dissociation curve, and can be identified by abnormal p50 measurements of patient red blood cells. Variants are categorized as either low oxygen affinity (high p50) or high oxygen affinity (low p50). Accurate diagnosis requires recognition of typical clinical and laboratory findings. In this case-based review, we present two patients with altered oxygen affinity variants, illustrating barriers to prompt and accurate diagnosis, and issues in management. We then review pathophysiology, diagnostic tests, clinical features, and management strategies.

High oxygen affinity hemoglobins

High oxygen affinity hemoglobins are responsible for rare and heterogeneous autosomic dominant genetic diseases. They cause pure erythrocytosis, sometimes accountable for hyperviscosity and thrombosis, or hemolysis. Differential diagnoses must be first ruled out. The diagnosis is based on the identification of a decreased P50, and their possible characterization by cation exchange-high performance liquid chromatography and capillary electrophoresis. Finally, genetic studies of the responsible globin chain gene will confirm the mutation. The prognosis mainly relies on the P50 decrease rate and on the hemoglobin cooperativity impairment. Disease management should be personalized, and it should primarily depend on smoking cessation and physical activity. Phlebotomy and platelet aggregation inhibitors' prescriptions can be discussed. There is no contraindication to flights, high-altitude conditions, or pregnancy. Nevertheless, blood donation must be prohibited.

Symptomatic Erythrocytosis Due to Homozygosity for Hb Luton [HBA2: c.269A>T (or HBA1)] and α-Thalassemia: A Clinical Update

A female proband homozygous for both Hb Luton [α89(FG1)His→Leu (CAC>CTC), HBA2: c.269A>T (or HBA1)], a high oxygen affinity hemoglobin (Hb), and for α(+)-thalassemia (α-thal), (-α(4.2), leftward deletion) was first described in 2012. This is a follow-up report of the same case. At the age of 18, the described patient presented with progressively worsening lethargy, headaches, dizziness, syncope and Raynaud's phenomenon. Following extensive cardiological and neurological investigation, it was felt that significant erythrocytosis was the most likely cause. Venesection followed by regular exchange transfusions were arranged with marked amelioration in symptomatology. In the vast majority of cases of high oxygen affinity Hbs, venesection is not recommended due to the asymptomatic phenotype and reduced oxygen delivery resulting from venesection. This update describes the evolving phenotype of this unique proband and, to the best of our knowledge, the first use of regular, long-term therapeutic red cell exchange transfusions in a case of high affinity Hb.

A Japanese Family with Congenital Erythrocytosis Caused by Haemoglobin Bethesda

We herein present a case of congenital erythrocytosis caused by haemoglobin (Hb) Bethesda in a Japanese family. A 55-year-old asymptomatic man was referred to our hospital for the investigation of erythrocytosis, which was present in other members of his family. The patient's serum erythropoietin level was normal, and the JAK2 V617F mutation was not detected. His P50 value was mildly decreased, thus we suspected the presence of an Hb variant with a high oxygen affinity. The high-performance liquid chromatography analysis showed an abnormal Hb, and by direct sequencing we identified the Hb Bethesda variant in this patient. For the differential diagnosis, we recommend the estimation of the P50 value as a practical and useful test.

Diagnosis and management of congenital and idiopathic erythrocytosis

An erythrocytosis occurs when there is an increased red-cell mass. The causes of erythrocytosis are divided into primary, when there is an intrinsic defect in the erythroid cell, and secondary, when the cause is extrinsic to the erythroid cell. An idiopathic erythrocytosis occurs when the increased red-cell mass has no identifiable cause. Primary and secondary defects can be further classified as either congenital or acquired causes. The diagnostic pathway starts with a careful history and examination followed by measurement of the erythropoietin (EPO) levels. This allows a division of those patients with a low EPO level, who can then be investigated for primary causes of erythrocytosis, and those with a normal or high EPO level, where the oxygen-sensing pathway needs to be explored further. Physiological studies in those with congenital defects in the oxygen-sensing pathway show many changes in the downstream metabolism adapting to the defect, which has a bearing on the management of the disorders. Low-dose aspirin and venesection to an achievable target are the main therapeutic options that can be considered in the management of erythrocytosis. Specific guidance on venesection options should be considered with certain causes such as high oxygen-affinity hemoglobins.

Secondary erythrocytosis due to compound homozygosity, but not compound heterozygosity, for Hb Luton and α-thalassemia: a family study

We describe the hematological and clinical features of homozygous Hb Luton (OMIM 141800.0172), a high affinity α-globin variant that has not been previously described in the homozygous state. The proband was found to have a high hemoglobin (Hb) concentration following a routine blood count prior to a planned appendectomy at the age of 16 years. Investigation showed that she was homozygous for both Hb Luton [α89(FG1)His→Leu (CAC>CTC), a high oxygen affinity Hb)] and homozygous for α(+)-thalassemia (α(+)-thal), while her mother, maternal aunt and half-brother were heterozygous for these conditions. Further investigation showed that she also had Gilbert's disease and Raynaud's syndrome. As far as we are aware, this is also the first reported family with a subject homozygous for both Hb Luton and α-thal so that the proband has no nomal α-globin. The parents of the proband are first cousins and originate from Pakistan.