Browsing by Author "Weatherall, D."

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Adaptation to anemia in hemoglobin E-beta thalassemia
(American Society of Hematology, 2010) Allen, A.; Fisher, C.; Premawardhena, A.; Peto, T.; Allen, S.J.; Arambepola, M.; Thayalsuthan, V.; Olivieri, N.; Weatherall, D.
Hemoglobin E beta thalassemia is the commonest form of severe thalassemia in many Asian countries. Its remarkably variable clinical phenotype presents a major challenge to determining its most appropriate management. In particular, it is not clear why some patients with this condition can develop and function well at very low hemoglobin levels. Here, we demonstrate that patients with hemoglobin E beta thalassemia have a significant decrease in the oxygen affinity of their hemoglobin, that is an increased P(50) value, in response to anemia. This may in part reflect the lower level of hemoglobin F in this condition compared with other forms of beta thalassemia intermedia. The ability to right-shift the oxygen dissociation curve was retained across the spectrum of mild and severe phenotypes, despite the significantly higher levels of hemoglobin F in the former, suggesting that efforts directed at producing a modest increase in the level of hemoglobin F in symptomatic patients with this disease should be of therapeutic value.
Alpha thalassaemia and extended alpha globin genes in Sri Lanka
(Elsevier-Academic Press, 2013) Suresh, S.; Fisher, C.; Ayyub, H.; Premawardhena, A.; Allen, A.; Perera, A.; Bandara, D.; Olivieri, N.; Weatherall, D.
The α-globin genes were studied in nine families with unexplained hypochromic anaemia and in 167 patients with HbE β thalassaemia in Sri Lanka. As well as the common deletion forms of α(+) thalassaemia three families from an ethnic minority were found to carry a novel form of α(0) thalassaemia, one family carried a previously reported form of α(0) thalassaemia, --(THAI), and five families had different forms of non-deletional thalassaemia. The patients with HbE β thalassaemia who had co-inherited α thalassaemia all showed an extremely mild phenotype and reduced levels of HbF and there was a highly significant paucity of α(+) thalassaemia in these patients compared with the normal population. Extended α gene arrangements, including ααα, αααα and ααααα, occurred at a low frequency and were commoner in the more severe phenotypes of HbE β thalassaemia. As well as emphasising the ameliorating effect of α thalassaemia on HbE β thalassaemia the finding of a novel form of α(0) thalassaemia in an ethnic minority, together with an unexpected diversity of forms of non-deletion α thalassaemia in Sri Lanka, further emphasises the critical importance of micro-mapping populations for determining the frequency of clinically important forms of the disease.
The Evolutionary and clinical implications of the uneven distribution of the frequency of the inherited haemoglobin variants over short geographical distances
(Wiley-Blackwell, 2017) Premawardhena, A.; Allen, A.; Piel, F.; Fisher, C.; Perera, L.; Rodrigo, R.; Goonathilaka, G.; Ramees, L.; Peto, T.; Olivieri, N.; Weatherall, D.
Studies of the frequency of heterozygous carriers for common inherited diseases of haemoglobin in over 7500 adolescent children in 25 districts in Sri Lanka have disclosed a highly significant variation over very short geographical distances. A further analysis of these findings, including their relationship to the past frequency and distribution of malaria, climatic variation, altitude, ethnic origin and consanguinity rates, have provided evidence regarding the evolutionary basis for the variable distribution of these conditions over short distances. It is likely that the complex interplay between malaria and the environment, together with related ethnic and social issues, exists in many countries across the tropical belt. Hence, these observations emphasise the importance of micromapping heterozygote distributions in high-frequency countries in order to define their true burden and the facilities required for the prevention and management of the homozygous and compound heterozygous disorders that result from their interaction.
Headache: an important symptom possibly linked to white matter lesions in thalassaemia.
(Wiley-Blackwell, 2019) Premawardhena, A.; Ranawaka, U.; Pilapitiya, T.; Weerasinghe, G.; Hapangama, A.; Hettiarachchi, S.; Salvin, K.; Silva, I.; Hameed, N.; Weatherall, M.; Olivieri, N.; Weatherall, D.
Neurological manifestations are reported only occasionally in patients with thalassaemia and are given much less prominence than the complications related to anaemia and iron overload. White matter changes (WMCs) on magnetic resonance imaging (MRI) in patients with thalassaemia were first reported two decades ago but the significance of these lesions remains unclear. We studied the neurological and cognitive manifestations in 82 older patients with thalssaemia [25 Thalassaemia major (TM), 24 thalassaemia intermedia (TI) and 33 haemaglobin E β thalassaemia (EBT)] and 80 controls, and found that headaches were more common in thalassaemia patients (50/82, 61%) than in controls (18/80, 22·5%: P < 0·001). WMCs on MRI were found in 20/82 (24·3%) patients and 2/29 (6·9%) controls had (P = 0·078). WMC were more common among those with headaches (17/50: 34%) than in those without headache (3/32; 9·3%) (P = 0·023). WMCs were not associated with reduction of cognition. Nevertheless, cognition was lower in the TI and EBT groups compared with those with TM (P = 0·002). The association of headache with WMC in thalassaemia has not been reported before and warrants further study.
Methemoglobinemia and ascorbate deficiency in hemoglobin E β thalassemia: metabolic and clinical implications.
(American Society of Hematology., 2012) Allen, A.; Fisher, C.; Premawardhena, A.; Bandara, D.; Perera, A.; Allen, S.; St Pierre, T.; Olivieri, N.; Weatherall, D.
ABSTRACT: During investigations of the phenotypic diversity of hemoglobin (Hb) E β thalassemia, a patient was encountered with persistently high levels of methemoglobin associated with a left-shift in the oxygen dissociation curve, profound ascorbate deficiency, and clinical features of scurvy; these abnormalities were corrected by treatment with vitamin C. Studies of erythropoietin production before and after treatment suggested that, as in an ascorbate-deficient murine model, the human hypoxia induction factor pathway is not totally dependent on ascorbate levels. A follow-up study of 45 patients with HbE β thalassemia showed that methemoglobin levels were significantly increased and that there was also a significant reduction in plasma ascorbate levels. Haptoglobin levels were significantly reduced, and the high frequency of the 2.2 haptoglobin genotype may place an additional pressure on ascorbate as a free-radical scavenger in this population. There was, in addition, a highly significant correlation between methemoglobin levels, splenectomy, and factors that modify the degree of globin-chain imbalance. Because methemoglobin levels are modified by several mechanisms and may play a role in both adaptation to anemia and vascular damage, there is a strong case for its further study in other forms of thalassemia and sickle-cell anemia, particularly when splenic function is defective.
The p.H63D allele of the HFE gene protects against low iron stores in Sri Lanka.
(Academic Press, 2019) Allen, A.; Premawardhena, A.; Allen, S.; Rodrigo, R.; Manamperi, A.; Perera, L.; Wray, K.; Armitage, A.; Fisher, C.; Drakesmith, A.; Robson, K.; Weatherall, D.
In hereditary hemochromatosis, iron overload is associated with homozygosity for the p.C282Y mutation. A second mutation, p.H63D, occurs at significant frequencies in Europe, North Africa, the Middle East and Asia. Early studies in Sri Lanka indicated that the variant had arisen independently, suggesting that it had been the subject of selective pressure. However, its role in iron absorption is unclear. In a survey of 7526 Sri Lankan secondary school students, we determined hemoglobin genotype and measured red cell indices, serum ferritin, transferrin receptor, iron zinc protoporphyrin and hepcidin. These variables were compared according to the presence or absence of the p.H63D variant in a subset of 1313 students for whom DNA samples were available. Students were classified as having low red cell indices if they had an MCV <80 fl and/or MCH <27 pg. Hetero and/or homozygosity for the p.H63D variant was more common in students with normal than low red cell indices (16.4% and 11.9% respectively; p = 0.019). Iron biomarkers and red cell indices were greater in children with the p.H63D variant than in normal and this was statistically significant for MCV (p = 0.046). Our findings suggest that selective pressure by mild iron deficiency contributes to the high frequencies of the p.H63D variant.
The variable phenotypes of haemoglobin D in Sri Lankan patients
(Sri Lanka Medical Association, 2006) Premawardhena, A.; Arambepola, M.; Weatherall, D.
INTRODUCTION: There are only few reports of the occurrence of the variant haemoglobin, haemoglobin D Punjab (β 121 Glu-Gln) in Sri Lanka and its clinical spectrum has not been well documented. MATERIALS AND METHODS: During the clinical study of patients attending the thalassaemia clinic at Teaching Hospital Kurunegala we identified several individuals with haemoglobin D, some of whom had co-inherited it with other haemoglobin disorders. They were diagnosed using High Performance Liquid Chromatography (Bio Rad, USA) and later confirmed by polymerase chain reaction. CLINICAL STUDIES: Family 1: (Hb D-p thalassaemia) Describes a family with two individuals with haemoglobin D- β thalassaemia. Both were mildly anaemic but had severe hypochromasia and microcytosis. They were otherwise well. Family 2: (Hb D- Hb S disease) The propositus was an eight year old girl who presented with several episodes of sickling crises. Parents were carriers for Hb S and Hb D. Family 3: (Hb D- Hb E disease) The propositus was an individual with Hb E- Hb D disease. She was clinically well and the only abnormality was severe hypochromasia and microcytosis. DISCUSSION: Hb D when co-inherited with Hb E or thalassaemia does not appear to cause clinically significant disease. The co-inheritance of Hb D with Hb S, however, results in severe disease leading to sickling crises. Even though Hb D commonly does not cause severe disease, knowledge of its occurrence is important as the hypochromasia and microcytosis associated with it may lead to unnecessary iron therapy.