A complex haemoglobinopathy diagnosis in a family with both beta zero- and alpha (zero/+)-thalassaemia homozygosity.
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The occurrence of point mutation alpha-thalassaemia and of complex combinations of haemoglobin defects is underestimated. Haemoglobinopathies, the most frequent monogenic recessive autosomal disorder in man, occur predominantly in Mediterranean, African and Asiatic populations. However, countries of immigration with a low incidence in the indigenous population, are now confronted with a highly heterogeneous array of imported defects. Furthermore, the occurrence of severe phenotypes is bound to increase in the near future because of the endogamous growth of the ethnical minorities and the lack of prevention. We describe an Afghan family in which both partners of a consanguineous relationship are carriers of a beta- as well as an alpha-thalassaemia determinant. The combination of defects was revealed by the in vitro measurement of the beta/alpha biosynthetic ratio and was characterised at the DNA level. The molecular defects involved are the Cd5(-CT), a Mediterranean beta zero-thalassaemia mutation, and the alpha 2(zero/+)-thalassaemia AATA(-AA) polyadenylation defect. The alpha-thalassemia defect is a rare RNA-processing mutant described only twice before in heterozygous form in Asian-Indian patients. The mutation suppresses the expression of a alpha 2 gene and reduces the expression of the less efficient, 3' located alpha 1 gene as well, inducing a near alpha zero-thalassaemia phenotype. This defect is now described for the first time in the homozygous condition in one of the children who, in addition to being homozygous for the alpha-thalassaemia point mutation, is also a carrier of the beta zero-thalassaemia defect. A previously described homozygous case of the alpha (zero/+)-thalassaemia condition, caused by a similar polyadenylation defect, was characterised by a severe HbH disease. However, the patient described here present at 7 years of age with severe caries, like his beta-thalassaemia homozygous brother but without hepatosplenomegaly, haemolysis or severe anaemia. The haematological analysis revealed 9.5 g/dl Hb; 5.4 x 10(12)/I RBC; 0.33 I/I PCV; 61 fl MCV; 17.6 pg MCH and 6.2% of HbA2. The biosynthetic ratio beta:alpha was 1.6 and no HbH fraction was detectable either on electrophoresis or as inclusion bodies. The parents reported no complications during pregnancy, at birth, or in the neonatal period in rural Afghanistan. We presume therefore that the counterbalancing effect induced by the co-existing beta-thalassaemia defect could have modified a potentially severe perinatal HbH disease into a strongly hypochromic but well compensated 'alpha zero-like heterozygous' thalassaemia phenotype. The risk of a severe HbH disease, could have been easily missed in this family which was referred because of a child affected with beta-thalassaemia major. (+info)
Cardiac blood flow studies in fetuses with homozygous alpha-thalassemia-1 at 12-13 weeks of gestation.
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OBJECTIVE: Fetuses affected by homozygous alpha-thalassemia-1 develop anemia as early as the first trimester. Our objective was to study hemodynamic indices in affected fetuses at 12-13 weeks of gestation to determine whether these would be useful in the prediction of anemia. DESIGN: Prospective observational study. SUBJECTS: Women referred before 14 weeks of gestation for the prenatal diagnosis of homozygous alpha-thalassemia-1. METHODS: Transabdominal and/or transvaginal Doppler sonography was performed to measure the flow velocities in the fetal ascending aorta and pulmonary artery at 12-13 weeks. The Doppler indices were compared between those that were subsequently confirmed to be affected by homozygous alpha-thalassemia-1 and those that were unaffected. RESULTS: Between June 1997 and April 1998, 60 eligible women were recruited. Doppler examination was successful in 58 fetuses. Of these, 22 were subsequently confirmed to be affected by homozygous alpha-thalassemia-1. The diagnosis was made by chorionic villus sampling and DNA analysis in two affected fetuses and by cordocentesis and hemoglobin evaluation in 20 affected fetuses. Hemoglobin concentrations could be measured in ten fetuses and these ranged from 4 to 8 g/dl. The affected fetuses had significantly higher peak velocities at the pulmonary valve and ascending aorta and a larger inner diameter of the pulmonary valve than that in unaffected fetuses. The total cardiac output was increased by one-third in affected fetuses and was mainly due to an increase of the right-side cardiac output. CONCLUSION: In the early stage of anemia, the fetus responds mainly by increasing its right-side cardiac output. However, there is extensive overlap of the values of cardiac output between the affected and the unaffected fetuses, precluding its use in the prediction of anemia. (+info)
Evaluation of a mutation screening strategy for sporadic cases of ATR-X syndrome.
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We report on the evaluation of a strategy for screening for XNP/ATR-X mutations in males with mental retardation and associated dysmorphology. Because nearly half of the mutations in this gene reported to date fall into a short 300 bp region of the transcript, we decided to focus in this region and to extend the mutation analysis to cases with a negative family history. This study includes 21 mentally retarded male patients selected because they had severe mental retardation and a typical facial appearance. The presence of haemoglobin H or urogenital abnormalities was not considered critical for inclusion in this study. We have identified six mutations which represents a mutation detection rate of 28%. This figure is high enough for us to propose this strategy as a valid first level of screening in a selected subset of males with mental retardation. This approach is simple, does not require RNA preparation, does not involve time consuming mutation detection methods, and can thus be applied to a large number of patients at a low cost in any given laboratory. (+info)
Intrathoracic extramedullary haematopoiesis complicated by massive haemothorax in alpha-thalassaemia.
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Intrathoracic extramedullary haematopoiesis (EMH) is a rare entity that is usually asymptomatic. A 44 year old man with alpha-thalassaemia is described who developed dyspnoea and massive left sided haemothorax. The haemoglobin disorder was established by Hgb H staining and haemoglobin electrophoretic studies. The DNA analysis revealed it to be a case of double heterozygous terminal codon mutation with the genotype alphaalphaCS/alphaalphaT. Computed tomographic scanning and magnetic resonance imaging of the thorax showed multiple paravertebral masses which were found by thoracoscopic biopsy to be extramedullary haematopoiesis. Although no additional sclerosing pleurodesis or low dose radiation therapy was given, the lung expanded well and there has been no recurrence of haemothorax to date. (+info)
Impairment of Plasmodium falciparum growth in thalassemic red blood cells: further evidence by using biotin labeling and flow cytometry.
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Certain red blood cell (RBC) disorders, including thalassemia, have been associated with an innate protection against malaria infection. However, many in vitro correlative studies have been inconclusive. To better understand the relationship between human RBCs with thalassemia hemoglobinopathies and susceptibility to in vitro infection, we used an in vitro coculture system that involved biotin labeling and flow cytometry to study the ability of normal and variant RBC populations in supporting the growth of Plasmodium falciparum malaria parasites. Results showed that both normal and thalassemic RBCs were susceptible to P falciparum invasion, but the parasite multiplication rates were significantly reduced in the thalassemic RBC populations. The growth inhibition was especially marked in RBCs from alpha-thalassemia patients (both alpha-thalassemia1/alpha-thalassemia2 and alpha-thalassemia1 heterozygote). Our observations support the contention that thalassemia confers protection against malaria and may explain why it is more prevalent in malaria endemic areas. (+info)
The contribution of alpha+-thalassaemia to anaemia in a Nigerian population exposed to intense malaria transmission.
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The proportion to which alpha-thalassaemia contributes to anaemia in Africa is not well recognized. In an area of intense malaria transmission in South-West Nigeria, haematological parameters of alpha-thalassaemia were examined in 494 children and 119 adults. The -alpha3.7 type of alpha+-thalassaemia was observed at a gene frequency of 0.27. Nine and 36.5% of individuals were homozygous and heterozygous, respectively. P.falciparum-infection was present in 78% of children and in 39% of adults. The alpha-globin genotypes did not correlate with the prevalence of P. falciparum-infection. alpha+-thalassaemic individuals had significantly lower mean values of haemoglobin, mean corpuscular volume, and mean corpuscular haemoglobin than non-thalassaemic subjects. Anaemia was seen in 54. 7% of children with a normal alpha-globin genotype, in 69.9% of heterozygous (odds ratio: 1.99, 95% confidence interval: 1.32-3.00, P = 0.001), and in 88.4% of homozygous alpha+-thalassaemic children (odds ratio: 7.72, 95% confidence interval: 2.85-20.90, P = 0.0001). The findings show that alpha+-thalassaemia contributes essentially to mild anaemia, microcytosis, and hypochromia in Nigeria. (+info)
A normal beta-globin allele as a modifier gene ameliorating the severity of alpha-thalassemia in mice.
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Thalassemia is a heritable human anemia caused by a variety of mutations that affect expression of the alpha- or the beta-chain of hemoglobin. The expressivity of the phenotype is likely to be influenced by unlinked modifying genes. Indeed, by using a mouse model of alpha-thalassemia, we find that its phenotype is strongly influenced by the genetic background in which the alpha-thalassemia mutation resides [129(sv/ev)/129(sv/ev) (severe) or 129(sv/ev)/C57BL/6 (mild)]. Linkage mapping indicates that the modifying gene is very tightly linked to the beta-globin locus (Lod score = 13.3). Furthermore, the severity of the phenotype correlates with the size of beta-chain-containing inclusion bodies that accumulate in red blood cells and likely accelerate their destruction. The beta-major globin chains encoded by the two strains differ by three amino acids, one of which is a glycine-to-cysteine substitution at position 13. The Cys-13 should be available for interchain disulfide bridging and consequent aggregation between excess beta-chains. This normal polymorphic variation between murine beta-globin chains could account for the modifying action of the unlinked beta-globin locus. Here, the variation in severity of the phenotype would not depend on a change in the ratio between alpha- and beta-chains but on the chemical nature of the normal beta-chain, which is in excess. This work also indicates that modifying genes can be normal variants that-absent an apparent physiologic rationale-may be difficult to identify on the basis of structure alone. (+info)
Nuchal translucency in fetuses affected by homozygous alpha-thalassemia-1 at 12-13 weeks of gestation.
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OBJECTIVE: Fetuses affected by homozygous alpha-thalassemia-1 are anemic in the first trimester. We studied their nuchal translucency (NT) measurements at 12-13 weeks of gestation. METHODS: Nuchal translucency was measured prospectively in fetuses at risk of homozygous alpha-thalassemia-1. Measurements of those fetuses subsequently confirmed to be affected by homozygous alpha-thalassemia-1 but with a normal karyotype were compared to those of 440 controls. The controls were from the general obstetric population who had NT measurements at 12 or 13 weeks with known normal outcome. All the NT measurements were expressed as multiples of the median (MoM) for the gestational day. RESULTS: Between 1996 and 1998, 94 at-risk pregnancies were studied. Of these, 32 were subsequently confirmed to be affected by homozygous alpha-thalassemia-1. Chromosome study was not carried out in three cases and these were excluded from the analysis. Nuchal translucency MoMs for cases and controls were found to fit a log Gaussian distribution. The log means (standard deviation) for case and control NT MoM were 0.075 (0.156) and -0.0019 (0.091), respectively. The median NT MoM (95% CI) for cases was 1.19 (1.08-1.62) and was significantly higher than that of the controls (p < 0.001). However, there was extensive overlap of NT between cases and controls. CONCLUSION: Overall, there was a 19% increase in NT MoM in fetuses affected by homozygous alpha-thalassemia-1. This represents a difference of only 0.3-0.4 mm, which is clinically insignificant. This finding indirectly suggests that the increased NT in trisomic fetuses cannot be explained by fetal anemia. Conversely, the presence of increased NT in a fetus at risk of homozygous alpha-thalassemia-1 should alert one to the possibility of chromosomal abnormality rather than being attributed to fetal anemia. (+info)