RESUMEN
Southeast Asian ovalocytosis (SAO) is characterized by the misfolding of band 3 protein in red blood cells (RBC). The abnormal structure of the band 3 protein results in dysmorphic RBC and related functions. Previous data showed that in vitro storage under hypothermic conditions alters band 3 protein structure and function. Microvesiculation includes shedding of RBC membranes, called RBC-derived microparticles/extracellular vesicles (RMP/EVs), and storage lesions. Unfortunately, there is no evidence of RBC microvesiculation under in vitro storage conditions in heterozygous SAO individuals. This study determined the generation of REVs and procoagulant activity during the storage of SAO blood samples in southern Thailand. Venous blood was collected from eight SAO and seven healthy individuals, preserved in citrate phosphate dextrose-adenine 1 (CPDA-1) at 4 °C for 35 days. The absolute numbers of REVs and PS-expressing RBCs were analyzed using flow cytometry. The procoagulant activity of the produced extracellular vesicles was determined by a clotting time assay. The results showed a significant increase in the number of REVs and PS-expressing RBCs in the SAO blood samples. Significantly correlated PS externalization and procoagulant activity were observed in the SAO blood samples. These lines of evidence indicate that the abnormality of the Band 3 protein is possibly involved in aberrant microvesiculation, exerting procoagulant activity in vitro. Increased pools of REV production and abnormal storage lesions in SAO blood samples should be a concern. Notably, the mechanisms underlying membrane vesiculation depend on the extent of blood cell storage under hypothermic conditions.
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BACKGROUND: Mutations in solute carrier family 4 member 1 (SLC4A1) encoding anion exchanger 1 (AE1) are the most common cause of autosomal recessive distal renal tubular acidosis (AR dRTA) in Southeast Asians. To explain the molecular mechanism of this disease with hematological abnormalities in an affected family, we conducted a genetic analysis of SLC4A1 and studied wild-type and mutant AE1 proteins expressed in human embryonic kidney 293T (HEK293T) cells. METHODS: SLC4A1 mutations in the patient and family members were analyzed by molecular genetic techniques. Protein structure modeling was initially conducted to evaluate the effects of mutations on the three-dimensional structure of the AE1 protein. The mutant kidney anion exchanger 1 (kAE1) plasmid construct was created to study protein expression, localization, and stability in HEK293T cells. RESULTS: We discovered that the patient who had AR dRTA coexisting with mild hemolytic anemia carried a novel compound heterozygous SLC4A1 mutations containing c.1199_1225del (p.Ala400_Ala408del), resulting in Southeast Asian ovalocytosis (SAO), and c.1331C > A (p.Thr444Asn). Homologous modeling and in silico mutagenesis indicated that these two mutations affected the protein structure in the transmembrane regions of kAE1. We found the wild-type and mutant kAE1 T444N to be localized at the cell surface, whereas the mutants kAE1 SAO and SAO/T444N were intracellularly retained. The half-life of the kAE1 SAO, T444N, and SAO/T444N mutants was shorter than that of the wild-type protein. CONCLUSION: These results suggest impaired trafficking and instability of kAE1 SAO/T444N as the likely underlying molecular mechanism explaining the pathogenesis of the novel SLC4A1 compound heterozygous mutation identified in this patient.
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Proteína 1 de Intercambio de Anión de Eritrocito , Riñón , Humanos , Proteína 1 de Intercambio de Anión de Eritrocito/química , Proteína 1 de Intercambio de Anión de Eritrocito/genética , Proteína 1 de Intercambio de Anión de Eritrocito/metabolismo , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Células HEK293 , Riñón/metabolismo , MutaciónRESUMEN
The Plasmodium vivax reticulocyte invasion process is still poorly understood, with only a few receptor-ligand interactions identified to date. Individuals with the Southeast Asian ovalocytosis (SAO) phenotype have a deletion in the band 3 protein on the surface of erythrocytes, and are reported to have a lower incidence of clinical P. vivax malaria. Based on this observation, band 3 has been put forward as a receptor for P. vivax invasion, although direct proof is still lacking. In this study, we combined functional ex vivo invasion assays and transcriptome sequencing to uncover a band 3-mediated invasion pathway in P. vivax and potential band 3 ligands. Invasion by P. vivax field isolates was 67%-71% lower in SAO reticulocytes compared with non-SAO reticulocytes. Reticulocyte invasion was decreased by 40% and 27%-31% when blocking with an anti-band 3 polyclonal antibody and a PvTRAg38 peptide, respectively. To identify new band 3 receptor candidates, we mRNA-sequenced schizont-stage isolates used in the invasion assays, and observed high transcriptional variability in multigene and invasion-related families. Transcriptomes of isolates with low or high dependency on band 3 for invasion were compared by differential expression analysis, which produced a list of band 3 ligand candidates with high representation of PvTRAg genes. Our ex vivo invasion assays have demonstrated that band 3 is a P. vivax invasion receptor and confirm previous in vitro studies showing binding between PvTRAg38 and band 3, although the lower and variable inhibition levels observed suggest the involvement of other ligands. By coupling transcriptomes and invasion phenotypes from the same isolates, we identified a list of band 3 ligand candidates, of which the overrepresented PvTRAg genes are the most promising for future research.
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Malaria Vivax , Plasmodium vivax , Proteína 1 de Intercambio de Anión de Eritrocito/metabolismo , Antígenos de Protozoos , Eliptocitosis Hereditaria , Eritrocitos , Humanos , Ligandos , Malaria Vivax/genética , Péptidos/metabolismo , Proteínas Protozoarias/metabolismo , ARN Mensajero/metabolismo , Reticulocitos/metabolismoRESUMEN
The bone marrow produces billions of reticulocytes daily. These reticulocytes mature into red blood cells by reducing their plasma membrane by 20% and ejecting or degrading residual internal organelles, membranes and proteins not required by the mature cell. This process occurs by autophagy, protein degradation and vesiculation but is not well understood. We previously reported that Southeast Asian Ovalocytic RBCs demonstrate incomplete reticulocyte maturation and we have now extended this study to a number of other variant RBCs. By comparing the profile of a pure reticulocyte preparation of cultured red cells with these variant cells, we show that the largest of these cells, the overhydrated hereditary stomatocytosis cells, are the least mature, they barely reduced their plasma membrane and contain large amounts of proteins that should have been reduced or removed. Intermediate sized variant RBCs appear to be more mature but retain some endoplasmic reticulum and residual membrane proteins. We propose that the size and composition of these variant cell types correlate with the different stages of reticulocyte maturation and provide insight into the reticulocyte maturation process.
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Background: Eosin-5-Maleimide (EMA)-based flow cytometry binds to red blood cell (RBC) membrane-associated proteins which can be used to detect red blood cell (RBC) membrane disorders. Myelodysplastic syndromes (MDS) are stem cell disorders resulting in ineffective hematopoiesis which is commonly present with anemia and erythroid dysplasia. Objectives: We aimed to study RBC membrane defects in MDS using flow cytometry for EMA staining. Methods: We enrolled anemic patients who were diagnosed with low-risk MDS (R-IPSS score ≤ 3.5), RBC membrane disorders [hereditary spherocytosis (HS) and Southeast Asian ovalocytosis (SAO)], and normal controls. Complete blood count (CBC) and flow cytometry for EMA staining were performed. Results: There were 16 cases of low-risk MDS, 6 cases of RBC membrane disorders, and 15 control cases. Mean fluorescence intensity (MFI) of EMA binding test in the RBC membrane disorders was significantly lower than controls (17.6 vs. 24.3, p < 0.001), but the EMA binding test in the low-risk MDS was not significantly different than the controls (26.5 vs. 24.3, p = 0.08). Conclusion: the RBC membrane defect in low-risk MDS was not demonstrated as having detection ability using EMA binding test with flow cytometry.
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BACKGROUND: The Sustainable development goals, which focus strongly on equity, aim to end all forms of malnutrition by 2030. However, a significant cause of intergenerational transfer of malnutrition, anaemia in pregnancy, is still a challenge. It is especially so in the low- and middle-income settings where possible context-specific aetiologies leading to anaemia have been poorly explored. This study explores the prevalence of etiological factors significantly contributing to anaemia in pregnancy in Sri Lanka, a lower-middle-income country with a high prevalence of malnutrition albeit robust public health infrastructure. METHODS: All first-trimester pregnant women registered in the public maternal care programme in the Anuradhapura district from July to September 2019 were invited to participate in Rajarata Pregnancy Cohort (RaPCo). After a full blood count analysis, high-performance liquid chromatography, peripheral blood film examination, serum B12 and folate levels were performed in anaemic participants, guided by an algorithm based on the red cell indices in the full blood count. In addition, serum ferritin was tested in a random subsample of 213 participants. Anaemic women in this subsample underwent B12 and folate testing. RESULTS: Among 3127 participants, 14.4% (95%CI 13.2-15.7, n = 451) were anaemic. Haemoglobin ranged between 7.4 to 19.6 g/dl. 331(10.6%) had mild anaemia. Haemoglobin ≥13 g/dl was observed in 39(12.7%). Microcytic, normochromic-normocytic, hypochromic-normocytic and macrocytic anaemia was observed in 243(54%), 114(25.3%), 80(17.8%) and two (0.4%) of full blood counts in anaemic women, respectively. Microcytic anaemia with a red cell count ≥5 * 106 /µl demonstrated a 100% positive predictive value for minor haemoglobinopathies. Minor hemoglobinopathies were present in at least 23.3%(n = 105) of anaemic pregnant women. Prevalence of iron deficiency, B12 deficiency and Southeast Asian ovalocytosis among the anaemic was 41.9% (95%CI 26.4-59.2), 23.8% (95%CI 10.6-45.1) and 0.9% (95%CI 0.3-2.3%), respectively. Folate deficiency was not observed. CONCLUSION: Even though iron deficiency remains the primary cause, minor hemoglobinopathies, B 12 deficiency and other aetiologies substantially contribute to anaemia in pregnancy in this study population. Public health interventions, including screening for minor hemoglobinopathies and multiple micronutrient supplementation in pregnancy, should be considered in the national programme for areas where these problems have been identified.
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Anemia/clasificación , Anemia/epidemiología , Anemia/etiología , Complicaciones Hematológicas del Embarazo/clasificación , Complicaciones Hematológicas del Embarazo/epidemiología , Complicaciones Hematológicas del Embarazo/etiología , Primer Trimestre del Embarazo , Adulto , Anemia/sangre , Estudios de Cohortes , Índices de Eritrocitos , Femenino , Ferritinas/sangre , Deficiencia de Ácido Fólico/complicaciones , Hemoglobinopatías/complicaciones , Hemoglobinas/análisis , Humanos , Deficiencias de Hierro/complicaciones , Embarazo , Complicaciones Hematológicas del Embarazo/sangre , Prevalencia , Sri Lanka/epidemiología , Deficiencia de Vitamina B 12/complicacionesRESUMEN
CONTEXT: Glycated hemoglobin A1c (HbA1c) level is used to screen and diagnose diabetes. Genetic determinants of HbA1c can vary across populations and many of the genetic variants influencing HbA1c level were specific to populations. OBJECTIVE: To discover genetic variants associated with HbA1c level in nondiabetic Malay individuals. DESIGN AND PARTICIPANTS: We conducted a genome-wide association study (GWAS) analysis for HbA1c using 2 Malay studies, the Singapore Malay Eye Study (SiMES, Nâ =â 1721 on GWAS array) and the Living Biobank study (Nâ =â 983 on GWAS array and whole-exome sequenced). We built a Malay-specific reference panel to impute ethnic-specific variants and validate the associations with HbA1c at ethnic-specific variants. RESULTS: Meta-analysis of the 1000 Genomes imputed array data identified 4 loci at genome-wide significance (Pâ <â 5â ×â 10-8). Of the 4 loci, 3 (ADAM15, LINC02226, JUP) were novel for HbA1c associations. At the previously reported HbA1c locus ATXN7L3-G6PC3, association analysis using the exome data fine-mapped the HbA1c associations to a 27-bp deletion (rs769664228) at SLC4A1 that reduced HbA1c by 0.38â ±â 0.06% (Pâ =â 3.5â ×â 10-10). Further imputation of this variant in SiMES confirmed the association with HbA1c at SLC4A1. We also showed that these genetic variants influence HbA1c level independent of glucose level. CONCLUSION: We identified a deletion at SLC4A1 associated with HbA1c in Malay. The nonglycemic lowering of HbA1c at rs769664228 might cause individuals carrying this variant to be underdiagnosed for diabetes or prediabetes when HbA1c is used as the only diagnostic test for diabetes.
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Proteína 1 de Intercambio de Anión de Eritrocito/genética , Glucemia/metabolismo , Eliminación de Gen , Hemoglobina Glucada/genética , Adolescente , Adulto , Anciano , Pueblo Asiatico/genética , Glucemia/genética , Estudios de Casos y Controles , Estudios de Cohortes , Estudios Transversales , Eliptocitosis Hereditaria/etnología , Eliptocitosis Hereditaria/genética , Etnicidad/genética , Etnicidad/estadística & datos numéricos , Femenino , Estudio de Asociación del Genoma Completo , Hemoglobina Glucada/metabolismo , Humanos , Malasia/epidemiología , Masculino , Persona de Mediana Edad , Polimorfismo Genético , Singapur/epidemiología , Adulto JovenRESUMEN
BACKGROUND: Familial distal renal tubular acidosis (dRTA) associated with mutations of solute carrier family 4 membrane - 1 (SLC4A1) gene could co-exist with red cell membrane abnormality, Southeast Asian ovalocytosis (SAO). Although this association is well described in Southeast Asian countries, it is less frequently found in Sri Lanka. CASE PRESENTATION: We describe six patients who had dRTA co-existing with SAO. All of them initially presented with severe hypokalemia and paralysis. They presented within a period of six months to the Teaching Hospital Anuradhapura, Sri Lanka. All had metabolic acidosis indicated by low serum bicarbonate. Three of them were having underlying chronic kidney disease as well. Those three patients had mixed high and normal anion gap metabolic acidosis indicated by low delta ratio. In all dRTA was confirmed by presence of normal anion gap, hyperchloraemia, high urine pH and positive urine anion gap. Examination of blood films of all of them revealed presence of stomatocytes and macro-ovalocytosis compatible with SAO. In relation to complications of dRTA, two patients had medullary nephrocalcinosis. Three patients had biochemical evidence of osteomalacia, with two of them having radiological evidence of diffuse osteosclerosis. One patient had secondary hyperparathyroidism and a pathological fracture. CONCLUSIONS: Erythrocyte in SAO is exceptionally rigid and this abnormality is said to be evolved as it protects against Plasmodium vivax malaria and cerebral malaria cause by Plasmodium falciparum. Although two families of SAO was described earlier, SAO and dRTA combination was reported only once in a patient from Anuradhapura district. Distal renal tubular acidosis, SAO combination and its related complications including nephrocalcinosis, chronic kidney disease and metabolic bone disease was not described in Sri-Lankan literature. This case series emphasize the importance of investigating recurrent/ chronic hypokalemia to diagnose dRTA and its associations, as early correction of acidosis could prevent development of chronic kidney disease and metabolic bone disease.
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Acidosis Tubular Renal/complicaciones , Enfermedades Óseas Metabólicas/complicaciones , Eliptocitosis Hereditaria/complicaciones , Equilibrio Ácido-Base , Acidosis Tubular Renal/sangre , Acidosis Tubular Renal/genética , Adulto , Proteína 1 de Intercambio de Anión de Eritrocito/genética , Bicarbonatos/sangre , Eliptocitosis Hereditaria/sangre , Femenino , Humanos , Hipopotasemia/sangre , Hipopotasemia/complicaciones , Masculino , Persona de Mediana Edad , Osteomalacia/complicaciones , Osteosclerosis , Sri LankaRESUMEN
Southeast Asian Ovalocytosis results from a heterozygous deletion of 9 amino acids in the erythrocyte anion exchange protein AE1 (band 3). The report of the first successful birth of an individual homozygous for this mutation showed an association with severe dyserythropoietic anemia. Imaging of the proband's erythrocytes revealed the presence of band 3 at their surface, a reduction in Wr(b) antigen expression, and increases in glycophorin C, CD44, and CD147 immunoreactivity. Immunoblotting of membranes from heterozygous Southeast Asian Ovalocytosis red cells showed a quantitative increase in CD44, CD147, and calreticulin suggesting a defect in reticulocyte maturation, as well as an increase in phosphorylation at residue Tyr359 of band 3, and peroxiredoxin-2 at the membrane, suggesting altered band 3 trafficking and oxidative stress, respectively. In vitro culture of homozygous and heterozygous Southeast Asian Ovalocytosis erythroid progenitor cells produced bi- and multi-nucleated cells. Enucleation was severely impaired in the homozygous cells and reduced in the heterozygous cells. Large internal vesicular accumulations of band 3 formed, which co-localized with other plasma membrane proteins and with the autophagosome marker, LC3, but not with ER, Golgi or recycling endosome markers. Immunoprecipitation of band 3 from erythroblast cell lysates at the orthochromatic stage showed increased interaction of the mutant band 3 with heat shock proteins, ubiquitin and cytoskeleton proteins, ankyrin, spectrin and actin. We also found that the mutant band 3 forms a strong interaction with non-muscle myosins IIA and IIB, while this interaction could not be detected in wild type erythroblasts. Consistent with this, the localization of non-muscle myosin IIA and actin was perturbed in some Southeast Asian Ovalocytosis erythroblasts. These findings provide new insights toward understanding in vivo dyserythropoiesis caused by the expression of mutant membrane proteins.
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INTRODUCTION: South-East Asian ovalocytosis (SAO) is a common inherited red blood cell polymorphism in South-East Asian and Melanesian populations, coinciding with areas of malaria endemicity. Validation of light microscopy as a diagnostic alternative to molecular genotyping may allow for its cost-effective use either prospectively or retrospectively by analysis of archived blood smears. METHODS: We assessed light microscopic diagnosis of SAO compared to standard PCR genotyping. Three trained microscopists each assessed the same 971 Giemsa-stained thin blood films for which SAO genotypic confirmation was available by PCR. Generalized mixed modeling was used to estimate the sensitivity, specificity, positive predictive value, and negative predictive value of light microscopy vs "gold standard" PCR. RESULTS: Among red cell morphologic parameters evaluated, knizocytes, rather than ovalocytic morphology, proved the strongest predictor of SAO status (odds ratio [OR] = 19.2; 95% confidence interval [95% CI] = 14.6-25.3; P ≤ 0.0001). The diagnostic performance of a knizocyte-centric microscopic approach was microscopist dependent: two microscopists applied this approach with a sensitivity of 0.89 and a specificity of 0.93. Inter-rater reliability among the microscopists (κ = 0.20) as well as between gold standard and microscopist (κ = 0.36) underperformed due to misclassification of stomatocytes as knizocytes by one microscopist, but improved substantially when excluding the error-prone reader (κ = 0.65 and 0.74, respectively). CONCLUSION: Light microscopic diagnosis of SAO by knizocyte visual cue performed comparable to time-consuming and costlier molecular methods, but requires specific training that includes successful differentiation of knizocytes from stomatocytes.
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Eliptocitosis Hereditaria , Eritrocitos Anormales , Microscopía/métodos , Reacción en Cadena de la Polimerasa/métodos , Asia Sudoriental , Eliptocitosis Hereditaria/sangre , Eliptocitosis Hereditaria/diagnóstico , Eliptocitosis Hereditaria/genética , Femenino , HumanosRESUMEN
Southeast asian ovalocytosis (SAO) is characterized by macro-ovalocytes and ovalo-stomatocytes on blood smear. SAO is common in Malaisia and Papua-New-Guinea where upwards to 40 per cent of the population is affected in some coastal region. Inherited in an autosomal dominant way, illness results from deletion of codons 400-408 in SLC4A1 gene which encodes for band 3 erythrocyte membrane protein. This deletion is responsible for an unusual erythrocyte stiffness and oval shape of the cells on blood smear. Heterozygous carriers are usually asymptomatic whereas homozygous are not viable without an intensive antenatal care. Here, we describe 4 patients diagnosed incidentally by cytogram appearance of the Advia® 2120i (Siemens) representing hemoglobin concentration according to red blood mean cellular volume (GR/VCH).
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Células Sanguíneas/patología , Eliptocitosis Hereditaria/diagnóstico , Hallazgos Incidentales , Adulto , Citodiagnóstico/métodos , Citodiagnóstico/normas , Eliptocitosis Hereditaria/sangre , Eliptocitosis Hereditaria/patología , Índices de Eritrocitos , Femenino , Pruebas Hematológicas , Humanos , Masculino , Persona de Mediana Edad , Embarazo , Complicaciones Hematológicas del Embarazo/sangre , Complicaciones Hematológicas del Embarazo/diagnóstico , Complicaciones Hematológicas del Embarazo/patología , Adulto JovenRESUMEN
The crystal structure of the dimeric membrane domain of human Band 3(1), the red cell chloride/bicarbonate anion exchanger 1 (AE1, SLC4A1), provides a structural context for over four decades of studies into this historic and important membrane glycoprotein. In this review, we highlight the key structural features responsible for anion binding and translocation and have integrated the following topological markers within the Band 3 structure: blood group antigens, N-glycosylation site, protease cleavage sites, inhibitor and chemical labeling sites, and the results of scanning cysteine and N-glycosylation mutagenesis. Locations of mutations linked to human disease, including those responsible for Southeast Asian ovalocytosis, hereditary stomatocytosis, hereditary spherocytosis, and distal renal tubular acidosis, provide molecular insights into their effect on Band 3 folding. Finally, molecular dynamics simulations of phosphatidylcholine self-assembled around Band 3 provide a view of this membrane protein within a lipid bilayer.
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Desequilibrio Ácido-Base/sangre , Acidosis Tubular Renal/sangre , Anemia Hemolítica Congénita/sangre , Proteína 1 de Intercambio de Anión de Eritrocito/química , Eliptocitosis Hereditaria/sangre , Errores Innatos del Metabolismo/sangre , Esferocitosis Hereditaria/sangre , Ácido 4,4'-Diisotiocianostilbeno-2,2'-Disulfónico/farmacología , Desequilibrio Ácido-Base/genética , Desequilibrio Ácido-Base/patología , Acidosis Tubular Renal/genética , Acidosis Tubular Renal/patología , Anemia Hemolítica Congénita/genética , Anemia Hemolítica Congénita/patología , Proteína 1 de Intercambio de Anión de Eritrocito/antagonistas & inhibidores , Proteína 1 de Intercambio de Anión de Eritrocito/genética , Proteína 1 de Intercambio de Anión de Eritrocito/metabolismo , Bicarbonatos/metabolismo , Eliptocitosis Hereditaria/genética , Eliptocitosis Hereditaria/patología , Eritrocitos/efectos de los fármacos , Eritrocitos/metabolismo , Eritrocitos/patología , Eritrocitos Anormales/patología , Expresión Génica , Glicosilación , Humanos , Ligandos , Errores Innatos del Metabolismo/genética , Errores Innatos del Metabolismo/patología , Mutación , Unión Proteica , Esferocitosis Hereditaria/genética , Esferocitosis Hereditaria/patologíaRESUMEN
Southeast Asian Ovalocytosis (SAO) is a common red blood cell disorder that is maintained as a balanced polymorphism in human populations. In individuals heterozygous for the SAO-causing mutation there are minimal detrimental effects and well-documented protection from severe malaria caused by Plasmodium vivax and Plasmodium falciparum; however, the SAO-causing mutation is fully lethal in utero when homozygous. The present-day high frequency of SAO in Island Southeast Asia indicates the trait is maintained by strong heterozygote advantage. Our study elucidates the evolutionary origin of SAO by characterizing DNA sequence variation in a 9.5 kilobase region surrounding the causal mutation in the SLC4A1 gene. We find substantial haplotype diversity among SAO chromosomes and estimate the age of the trait to be approximately 10,005 years (95% CI: 4930-23,200 years). This date is far older than any other human malaria-resistance trait examined previously in Southeast Asia, and considerably pre-dates the widespread adoption of agriculture associated with the spread of speakers of Austronesian languages some 4000 years ago. Using a genealogy-based method we find no evidence of historical positive selection acting on SAO (s=0.0, 95% CI: 0.0-0.03), in sharp contrast to the strong present-day selection coefficient (e.g., 0.09) estimated from the frequency of this recessively lethal trait. This discrepancy may be due to a recent increase in malaria-driven selection pressure following the spread of agriculture, with SAO targeted as a standing variant by positive selection in malarial populations.
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Proteína 1 de Intercambio de Anión de Eritrocito/genética , Eliptocitosis Hereditaria/genética , Malaria/genética , Asia Sudoriental , Evolución Molecular , Femenino , Frecuencia de los Genes , Estudios de Asociación Genética , Predisposición Genética a la Enfermedad , Haplotipos , Humanos , Desequilibrio de Ligamiento , Masculino , Polimorfismo de Nucleótido Simple , Selección Genética , Análisis de Secuencia de ADNRESUMEN
The structure and function of the red cell anion exchanger 1 (AE1, Band 3, SLC4A1), the truncated kidney anion exchanger 1 (kAE1), and the other members of the SLC4 family of bicarbonate transporters are reviewed. Mutations in the AE1 gene cause human diseases like Southeast Asian ovalocytosis and hereditary spherocytosis in the red cell and distal renal tubular acidosis in the kidney. These mutations affect the folding, trafficking, and functional expression of these membrane glycoproteins. In the SLC26 family of anion transporters, mutations also cause trafficking defects and human disease. Membrane glycoproteins are cotranslationally N-glycosylated in the endoplasmic reticulum (ER) and when properly folded, traffic via the secretory pathway to their final destination such as the plasma membrane. Misfolded glycoproteins are retained in ER and are targeted for degradation by the proteasome following retrotranslocation and ubiquitinylation. ER chaperones, like membrane-bound calnexin, interact transiently with glycoproteins and are part of the quality control system that monitors the folding of glycoproteins during their biosynthesis. Recent results have indicated that it is possible to "correct" trafficking defects caused by some mutations in the SLC4 and 26 families through the use of small molecules that interfere with the interaction of glycoproteins with the components of the quality control system. This review summarizes the current knowledge on structure and function of anion transporters from the SLC4 and SLC26 families, and the effect of mutations on their trafficking and functional expression.
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Proteínas de Transporte de Anión/química , Proteínas de Transporte de Anión/metabolismo , Animales , Proteínas de Transporte de Anión/biosíntesis , Proteínas de Transporte de Anión/genética , Células Eritroides/metabolismo , Glicosilación , Humanos , Riñón/metabolismo , Mutación , Transporte de ProteínasRESUMEN
We have detected an ovalo-stomatocytosis in a military 24-years-old man. We have sent a blood specimen to haematology laboratory in Kremlin-Bicetre (France) to test ektacytometry. The test concludes to an asymptomatic Melanesian ovalocytosis.
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Eliptocitosis Hereditaria/diagnóstico , Eliptocitosis Hereditaria/sangre , Pruebas Hematológicas , Humanos , Masculino , Personal Militar , Adulto JovenRESUMEN
The molecular approaches to distal renal tubular acidosis (dRTA) associated AE1 mutations lead us to understand the genetic and pathophysiological aspects of the acidification defects. An unanticipated high value of the urine-blood (U-B) PCO(2) after NaHCO(3) loading observed in a case of dRTA and southeast Asian ovalocytosis (SAO) might be from a mistarget of the AE1 to the luminal membrane of type A intercalated cells. The mutations of the AE1 gene resulted in SAO and also affected renal acidification function. Notwithstanding, after the NH4Cl loading in 20 individuals with SAO, the acidification in the distal nephron was normal. The presence of both SAO and G701D mutations of AE1 gene would explain the abnormal urinary acidification in the patients with the compound heterozogosity. In terms of the effect of the mutations on trafficking of AE1, truncated kidney isoform (kAE1) of wild-type showed a 'dominant-positive effect' in rescuing the recessive mutant kAE1 (S773P or G701D) trafficking to the plasma membrane, in contrast with the dominant mutant kAE1 (R589H) resulting in a 'dominant-negative effect' when heterodimerized with the wild-type kAE1. It is notable that the dominant mutants kAE1 (R901X or G609R) expression in MDCK cells clearly results in aberrant surface expression with some mutant protein appearing at the apical membrane. These might result in net bicarbonate secretion and increasing U-B PCO(2) in the distal nephron. The molecular physiological and genetic approaches have permitted identification of the molecular defects, predominantly in transporter proteins, and should in turn prompt development of novel therapeutic strategies.
RESUMEN
The molecular approaches to distal renal tubular acidosis (dRTA) associated AE1 mutations lead us to understand the genetic and pathophysiological aspects of the acidification defects. An unanticipated high value of the urine-blood (U-B) PCO2 after NaHCO3 loading observed in a case of dRTA and southeast Asian ovalocytosis (SAO) might be from a mistarget of the AE1 to the luminal membrane of type A intercalated cells. The mutations of the AE1 gene resulted in SAO and also affected renal acidification function. Notwithstanding, after the NH4Cl loading in 20 individuals with SAO, the acidification in the distal nephron was normal. The presence of both SAO and G701D mutations of AE1 gene would explain the abnormal urinary acidification in the patients with the compound heterozogosity. In terms of the effect of the mutations on trafficking of AE1, truncated kidney isoform (kAE1) of wild-type showed a 'dominant-positive effect' in rescuing the recessive mutant kAE1 (S773P or G701D) trafficking to the plasma membrane, in contrast with the dominant mutant kAE1 (R589H) resulting in a 'dominant-negative effect' when heterodimerized with the wild-type kAE1. It is notable that the dominant mutants kAE1 (R901X or G609R) expression in MDCK cells clearly results in aberrant surface expression with some mutant protein appearing at the apical membrane. These might result in net bicarbonate secretion and increasing U-B PCO2 in the distal nephron. The molecular physiological and genetic approaches have permitted identification of the molecular defects, predominantly in transporter proteins, and should in turn prompt development of novel therapeutic strategies.