Mechanistic basis of low blood pressure and association of red cell distribution width with β-globin gene mutation patterns in Bangladeshi patients with E-β/β-thalassemia major

Abstract

Background Thalassemia has been recognized as a global public health problem. Bangladesh, with a carrier frequency of 11%, including 2% with β trait and 9% with E trait is negatively affected with this monogenic blood disorder. There may be as many as 100,000 transfusion-dependent thalassemia patients in the country. Among many of problems, low blood pressure has been observed in the patients with β- thalassemia major (BTM) and hemoglobin E/β-thalassemia (EBT). Again, various mutations in the β-globin gene have been known to result in heterogeneous clinical manifestations in the patients with thalassemia. For instance, the patients with EBT who require transfusions have varying degrees of transfusion frequency, while those with β-thalassemia major (BTM) require transfusions on a monthly or more frequent basis and also chelation therapy. Objectives The aim of this research was to explore (1) the underlying mechanisms of low blood pressure and (2) the impact of different mutant genotypes in the β-globin gene on red cell distribution width (RDW) in patients with β-thalassemia major (BTM) and hemoglobin E/β-thalassemia (EBT). Study Population and Methodology The study enrolled a total of 218 patients, consisting of 106 patients with BTM and 112 patients with EBT. Also, the study recruited 200 healthy controls. In order to determine the underlying cause of low blood pressure, several parameters which are known to affect blood pressure were assessed. The target parameters included oxygen saturation, partial pressure of oxygen, plasma albumin, plasma calcium, serum electrolytes (sodium and potassium), as well as blood free carnitine and acylcarnitine. Molecular analysis was performed using PCR followed by Sanger sequencing of HBB genes. Considering that various mutations are anticipated to impact red blood cell (RBC) volume and size in distinct ways to introduce varying degrees of heterogeneity; several RBC indices were measured using automated hematology analyzer. The targeted RBC indices included hemoglobin (Hb), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and red cell distribution width (RDW). Results Although every patient diagnosed with BTM and EBT demonstrated decreased systolic and diastolic blood pressure, the group experiencing the most severe symptoms, which involved blood transfusions occurring at an interval of 30 days or less, exhibited the lowest blood pressure levels. This finding suggests a relationship between disease severity and a decline in blood pressure in these individuals. In the studied patients with BTM and EBT, it was found that oxygen status did not play a significant role in contributing to low blood pressure. The study revealed that patients with β thalassemia major (BTM) and E/β-thalassemia (EBT) had significantly low levels of plasma albumin and calcium. Furthermore, the most severe group, which necessitated more frequent blood transfusions, exhibited the lowest levels of these parameters (p= <0.05). Although the potassium levels in these patients were generally found within the normal range in the patients with both BTM and EBT, the most severe group of patients with β thalassemia major (BTM) and E/β-thalassemia (EBT) exhibited hyponatremia, indicating lower-than-normal sodium levels in their blood. While medium chain acylcarnitine levels were similar among the patients with β thalassemia major (BTM), hemoglobin E/βthalassemia (EBT), and healthy controls, significant differences in concentrations were observed for free carnitine, acetylcarnitine, short chain acylcarnitines, long chain acylcarnitines based on blood transfusion intervals (P<0.05). Moreover, an impaired fatty acid oxidation rate exhibited by reduced free carnitine to acetylcarnitine ratio, was observed in the patients with BTM. DNA sequencing of the haemoglobin gene, detected ten different mutations, including c.CD26, IVS-1_5G>C, c.124-127delCTTT, c.G47A, c.CD30G>C, IVS1_130 G>C, c.126delC, c.27-28insG, c.51delC and c.33C>A, in β-globin gene. The analysis of hematological indices demonstrated elevated values of red cell distribution width (RDW) in the patients with both β thalassemia major (BTM) and E/β-thalassemia (EBT) compared to the healthy controls. Furthermore, when examining hematological indices alongside genetic analyses, it was found that regardless of mutational status, EBT patients exhibited higher RDW values than the patients with BTM. Moreover, among EBT patients with varying degrees of transfusion intervals, those who required less frequent blood transfusion had the highest RDW values. Conclusion Hypotension in the patients with BTM and EBT may be caused by the additive effects of hyponatremia, hypocalcemia, hypoalbuminemia, low levels of carnitine and acetylcarnitines and reduced free carnitine to acylcarnitine ratio. Thus, management of the condition with supplementation of the aforementioned components can be expected to improve blood pressure as well as the quality of life of the patients with BTM and EBT. The varying degrees of RDW may be due to presence of different mutant genotypes in the β-globin gene, which may be associated with different disease manifestations. The RDW can thus give an idea about the spectrum, progression, severity, and prognosis of thalassemia. This study thus suggests that RDW can be used as an indicator to give individualized treatment for the patients with β-thalassemia, such as increasing the blood transfusion interval in the patients with higher RDW. In addition, RDW information may be used to distinguish between patients with severe and mildly severe and other clinical manifestations of E-β thalassemia patients and also between the patients with β-thalassemia major and E-β thalassemia.