HMIP-2 is a human quantitative trait locus affecting peripheral numbers, size and hemoglobin composition of red blood cells, with a marked effect on the persistence of the fetal form of hemoglobin, HbF, in adults. The locus consists of multiple common variants in an enhancer region for MYB (chr 6q23.3), which encodes the hematopoietic transcription factor cMYB. Studying a European population cohort and four African-descended groups of patients with sickle cell anemia, we found that all share a set of two spatially separate HbF-promoting alleles at HMIP-2, termed "A" and "B." These typically occurred together ("A-B") on European chromosomes, but existed on separate homologous chromosomes in Africans. Using haplotype signatures for "A" and "B," we interrogated public population datasets. Haplotypes carrying only "A" or "B" were typical for populations in Sub-Saharan Africa. The "A-B" combination was frequent in European, Asian, and Amerindian populations. Both alleles were infrequent in tropical regions, possibly undergoing negative selection by geographical factors, as has been reported for malaria with other hematological traits. We propose that the ascertainment of worldwide distribution patterns for common, HbF-promoting alleles can aid their further genetic characterization, including the investigation of gene-environment interaction during human migration and adaptation.
Transfusion of red blood cells is a major therapeutic option in sickle cell disease (SCD). There is strong evidence for its efficacy, particularly in primary and secondary stroke prevention in children, however, its use in other areas remains controversial. This study assessed the patterns of transfusion in the adult cohort attending Kings College Hospital over a 10-year period, from 2000 to 2009. Total blood usage has increased significantly (P = 0·006) during this time, with 78% of the blood received by only 6% of the patients. The increase is explained by increased automated red cell exchange and increased usage for planned and acute transfusions for sickle-related complications.
Fetal hemoglobin (HbF, ?(2)?(2)) is a major contributor to the remarkable phenotypic heterogeneity of sickle cell anemia (SCA). Genetic variation at 3 principal loci (HBB cluster on chromosome 11p, HBS1L-MYB region on chromosome 6q, and BCL11A on chromosome 2p) have been shown to influence HbF levels and disease severity in ?-thalassemia and SCA. Previous studies in SCA, however, have been restricted to populations from the African diaspora, which include multiple genealogies. We have investigated the influence of these 3 loci on HbF levels in sickle cell patients from Tanzania and in a small group of African British sickle patients. All 3 loci have a significant impact on the trait in both patient groups. The results suggest the presence of HBS1L-MYB variants affecting HbF in patients who are not tracked well by European-derived markers, such as rs9399137. Additional loci may be identified through independent genome-wide association studies in African populations.
Sickle cell anemia is caused by a single type of mutation, a homozygous A?T substitution in the ß globin gene. Clinical severity is diverse, partially due to additional, disease-modifying genetic factors. We are studying one such modifier locus, HMIP (HBS1L-MYB intergenic polymorphism, chromosome 6q23.3). Working with a genetically admixed patient population, we have encountered the necessity to generate haplotype signatures of genetic markers to label genomic fragments with distinct genealogical origin at this locus. With the goal to generate haplotype signatures from patients experimentally, we have investigated the suitability of an existing nanofluidic assay platform to perform phase alignment with single-nucleotide polymorphism alleles.
Hepcidin is known to be a key systemic iron-regulatory hormone which has been demonstrated to be associated with a number of iron disorders. Hepcidin concentrations are increased in inflammation and suppressed in hemochromatosis. In view of the role of hepcidin in disease, its potential as a diagnostic tool in a clinical setting is evident. This study describes the development of a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) assay for the quantitative determination of hepcidin concentrations in clinical samples. A stable isotope labeled hepcidin was prepared as an internal standard and a standard quantity was added to urine samples. Extraction was performed with weak cation-exchange magnetic nanoparticles. The basic peptides were eluted from the magnetic nanoparticles using a matrix solution directly onto a target plate and analyzed by MALDI-TOF MS to determine the concentration of hepcidin. The assay was validated in charcoal stripped urine, and good recovery (70-80%) was obtained, as were limit of quantitation data (5 nmol/L), accuracy (RE <10%), precision (CV <21%), within -day repeatability (CV <13%) and between-day repeatability (CV <21%). Urine hepcidin levels were 10 nmol/mmol creatinine in healthy controls, with reduced levels in hereditary hemochromatosis (P < 0.000005) and elevated levels in inflammation (P < 0.0007). In summary a validated method has been developed for the determination of hepcidin concentrations in clinical samples.
Hepcidin is a peptide hormone that functions as a key regulator of mammalian iron metabolism. Serum and urine levels are increased in inflammation and suppressed in hemochromatosis, and they may have diagnostic importance. This study describes the development and validation of an analytical method for the quantitative determination of the concentration of hepcidin in clinical samples. A stable, isotopically labeled internal standard, [15N,13C2]Gly12,20-hepcidin, was synthesized and a standard quantity was added to urine samples. Extraction was performed using weak cation exchange magnetic nanoparticles. An ion trap mass spectrometer was used to quantify hepcidin in the samples. The hepcidin assay was validated, and good recovery of hepcidin was obtained. The assay is accurate and precise. Urinary hepcidin levels of 3 to 9 nmol/mmol creatinine(-1) were found in healthy controls, with reduced levels in hemochromatosis (P<0.00006) and elevated levels in inflammation (P<0.00035). In sickle cell disease, a wide range was found, with the mean value not differing significantly from controls (P<0.26). In summary, a validated method has been developed for the quantitation of hepcidin using a stable, isotopically labeled internal standard and applied to determine the concentrations of hepcidin in the low nanomolar range in urine samples from patients and controls.
Spin density projection-assisted R2-magnetic resonance imaging (R2-MRI; FerriScan(®)) scans from 40 chelation-naïve sickle cell patients were used to assess renal iron load by measuring renal R2 (R-R2). Clinical data were collected retrospectively for the 2-year period preceding the scan. R-R2 showed no significant correlation with transfusional iron load (assessed by liver iron concentration), but correlated significantly with serum bilirubin (R = 0·61, P < 0·0001) and lactate dehydrogenase (R = 0·58, P < 0·0001). Mean (±standard deviation) R-R2 was higher (P = 0·02) in patients with renal hyperfiltration (29·8 ± 10·3/s) than those without (23·11 ± 6·6/s). Five patients had significantly lower signal intensity in the renal cortex, as compared to the medulla. These patients had a significantly higher (P < 0·0001) mean R-R2 than those showing no cortico-medullary difference. We postulate that the increased R-R2 is associated with haemolysis rather than transfusional iron load in sickle cell disease.
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