Hb Washtenaw [ beta 11(A8)Val-->Phe]: an electrophorectically silent, unstable, low oxygen affinity variant associated with anemia and chronic cyanosis

Pathology consultation on HbA(1c) methods and interferences

OBJECTIVES

To review the various hemoglobin (Hb) A1c methods, with a focus on interferences resulting from Hb variants.

METHODS

HbA1c is a marker used for the diagnosis and management of diabetes. Each available HbA1c method has advantages and challenges, such as its susceptibility to interferences.

RESULTS

The presence of Hb variants and/or abnormalities in RBC turnover cannot only interfere analytically with HbA1c measurements but also may affect the clinical interpretation of HbA1c values.

CONCLUSIONS

Familiarity with the advantages and challenges of the various methods used for HbA1c testing is essential when establishing therapeutic management and goals based on HbA1c results, especially in populations with a high prevalence of Hb variants.

Pleiotropic effects of intravascular haemolysis on vascular homeostasis

The breakdown of senescent or defective red blood cells releases red cell contents, especially haemoglobin, which scavenges nitric oxide (NO) and decomposes to haem and free iron. These are potent oxidants, all of which have promoted the evolution of inducible and vasculoprotective compensatory pathways to rapidly clear and detoxify haemoglobin, haem and iron. Chronic haemolytic red cell disorders as diverse as sickle cell disease, thalassaemia, unstable haemoglobinopathy, cytoskeletal defects and enzymopathies have been linked to a clinical constellation of pulmonary hypertension, priapism, leg ulceration and possibly cerebrovascular disease and thrombosis. Besides free haemoglobin, haemolysis has been associated with extracellular arginase that limits substrate availability to NO synthase, endogenous inhibitors of NO synthase activity, and inappropriate activation of haemostatic pathways. This article reviews the haemolytic disorders that have been reported to manifest vascular complications, and explores the speculative possibility that haemolysis mediates some of the vascular complications of inflammation and diabetes.

Hemoglobin disorders and endothelial cell interactions

Endothelial damage and inflammation make a significant contribution to the pathophysiology of sickle cell disease (SCD) and the beta-thalassemia syndromes. Endothelial dysfunction and ensuing vasculopathy are implicated in pulmonary hypertension in the hemoglobinopathies and endothelial activation and endothelial-blood cell adhesion, accompanied by inflammatory processes and oxidative stress, are imperative to the vaso-occlusive process in SCD. Herein, we discuss the role that the endothelium plays in all of these processes and the effect that genetic modifiers and hydroxyurea therapy may have upon endothelial interactions. Therapies targeting the endothelium and endothelial interactions may represent a promising approach for treating these diseases.

Abnormal haemoglobins, Hb Takamatsu and Hb G-Szuhu, detected during the analysis of glycated haemoglobin (HbA1C) by high performance liquid chromatography

BACKGROUND

During medical checkups of two unrelated female outpatients during their annual health examination and one male inpatient suffering from cardiac failure the glycated haemoglobin (HbA1C) concentrations measured by high performance liquid chromatography (HPLC) were low, in spite of normal fasting plasma glucose concentrations. However, HbA1C concentrations measured by latex immunoagglutination and fructosamine concentrations were within the normal range.

METHOD

Investigations were performed to elucidate the reasons for these discrepancies.

RESULTS

Abnormal haemoglobins, Hb Takamatsu and Hb G-Szuhu, were found. The HPLC chromatogram showed an additional peak near HbA1a + b, which resulted in falsely low HbA1C concentrations. Isoelectric focusing analysis of the patients' haemoglobin disclosed abnormal haemoglobins, which migrated faster than normal HbA1 in the two female patients and slower in the male patient. The cDNA sequence and amino acid analyses of the haemoglobin alpha-chains and beta-chains indicated the presence of the haemoglobin variant beta 120 Lys-->Gln in the two female patients and beta 80 Asn-->Lys in the male patient; that is, Hb Takamatsu and Hb G-Szuhu.

CONCLUSIONS

These cases show how these silent haemoglobin variants can result in falsely low HbA1C concentration readings when using HPLC.

delta-Thalassemic phenotype due to two "novel" delta-globin gene mutations: CD11[GTC-->GGC (A8)-HbA2-Pylos] and CD 85[TTT-->TCT(F1)-HbA2-Etolia]

delta-Thalassemia reduces the expected HbA2 percentage, altering the normal as well as the beta-thalassemia trait phenotype. An attempt to elucidate the molecular basis of delta-thalassemia in the Greek population, revealed two cases with unknown molecular defects that presented low levels of HbA2 (about 1.5%). DNA sequence analysis of delta-globin gene identified two "novel" mutations in the coding regions of the gene; the cd11 (GTC-->GGC) resulting in the substitution of valine for glycine (:HbA2-Pylos) and the cd85(TTT-->TCT) resulting in the substitution of phenylalanine for serine (:HbA2-Etolia). Because these mutations are localized at the helical positions A8 and F1 of the HbA2 respectively, they potentially cause molecular instability of the tetramer, thus leading to reduced HbA2 percentage.

Familial association of primary pulmonary hypertension and a new low-oxygen affinity beta-chain hemoglobinopathy, Hb Washtenaw

A Hungarian-American kindred with familial primary pulmonary hypertension (PPH) and a new, low-oxygen affinity beta-chain variant hemoglobin, Hb Washtenaw, is described. The index case presented with severe PPH and was found to have the abnormal hemoglobin. Two siblings with the abnormal hemoglobin also demonstrated increased pulmonary artery pressures on exercise echocardiography suggestive of early PPH. The occurrence of PPH and the abnormal hemoglobin could be due to genetic or biochemical factors or simply coincidental. A previous study had described a possible association of an abnormal beta-chain variant hemoglobin, Hb Warsaw, and PPH. It was suggested that the putative gene for familial PPH may be located near the beta-globin gene on chromosome 11. The association of PPH and the beta-chain variant hemoglobin in this kindred adds further support to this hypothesis.

Priapism following splenectomy in an unstable hemoglobin: hemoglobin Olmsted beta 141 (H19) Leu-->Arg

We report a case of severe priapism occurring in a patient with an unstable hemoglobin, Hb Olmsted (beta 141 Leu-->Arg) This is a rare hemoglobin variant, which until now has been reported only once. The clinical course of the 12-year-old boy was characterized by severe hemolytic anemia leading to splenectomy and cholecystectomy at the of 3.5 years. The priapism occurred 8 years after splenectomy, during a hemolytic febrile episode and required aspiration of the corpora cavernosa. This report raises the question of the benefit of splenectomy in patients suffering from a chronic hemolytic anemia such as that due to an unstable hemoglobin. This treatment lowers the frequency and the severity of acute hemolytic attacks, but several cases of vascular complications have been reported after splenectomy.