Red Cell Traits Research Articles

Genetic architecture of routinely acquired blood tests in a British South Asian cohort

Understanding the genetic basis of routinely-acquired blood tests can provide insights into several aspects of human physiology. We report a genome-wide association study of 42 quantitative blood test traits defined using Electronic Healthcare Records (EHRs) of ~50,000 British Bangladeshi and British Pakistani adults. We demonstrate a causal variant within the PIEZO1 locus which was associated with alterations in red cell traits and glycated haemoglobin. Conditional analysis and within-ancestry fine mapping confirmed that this signal is driven by a missense variant - chr16-88716656-G-TT - which is common in South Asian ancestries (MAF 3.9%) but ultra-rare in other ancestries. Carriers of the T allele had lower mean HbA1c values, lower HbA1c values for a given level of random or fasting glucose, and delayed diagnosis of Type 2 Diabetes Mellitus. Our results shed light on the genetic basis of clinically-relevant traits in an under-represented population, and emphasise the importance of ancestral diversity in genetic studies.

Abstract 25: Epigenome-Wide DNA Methylation Analysis Reveals Novel Hematologic Trait Associations for African Americans in The Jackson Heart Study

Cardiovascular disease (CVD) is the leading cause of death in the U.S. and disproportionately affects African Americans (AAs). Routinely measured circulating red blood cell traits, which are highly heritable and differ by ethnicity, are independent predictors for CVD-related traits including hypertension, stroke, coronary heart disease, and CVD mortality. Many genetic loci associated with red blood cell count (RBC), hemoglobin (HGB), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and red cell distribution width (RDW) have been identified. However, identified genetic variants do not fully explain the heritability of these traits. Epigenetic alterations in DNA methylation likely also explain a portion of red cell trait variance, and detecting methylation quantitative trait loci (meQTLs) can provide critical insight into the development of CVD and CVD health disparities. We performed an epigenome-wide association analysis to identify CpG sites at which DNA methylation levels are associated with red blood cell traits in 1753 participants from the Jackson Heart Study, a population-based cohort of AAs. DNA methylation was measured by the Illumina MethylationEPIC array, interrogating approximately 850,000 CpG sites in peripheral blood mononuclear cells at the baseline exam. Associations were assessed using linear mixed models adjusted for age, sex, cell proportions, genetic ancestry, and experimental batch effects. A Bonferroni-corrected p-value of 9x10 -8 was used to assess statistical significance. We identified many significant differentially methylated CpG sites associated with red blood cell traits. Analysis of RBC, HGB, MCV, MCH, and MCHC revealed a novel highly significant association with a CpG annotated to a non-coding RNA (cg11703701; RBC P = 5.19x10 -22 , HGB P = 1.19x10 -11 , MCV P = 4.69x10 -59 , MCH P = 2.68x10 -67 , MCHC P = 2.32x10 -31 ), as well as a strong signal for a reprogramming-specific differentially methylated region (cg04321267; RBC P = 1.67x10 -16 , HGB P = 3.58x10 -12 , MCV P = 2.12x10 -49 , MCH P = 1.74x10 -57 , MCHC P = 5.91x10 -30 ). Multiple CpGs annotated to genes HBA1 and HBA2 were associated with RBC, MCV, MCH, and MCHC, while ITPKB (cg23740281; HGB P = 4.88x10 -10 , HCT P = 6.20x10 -11 ) and ALDH2 (cg17969951; HGB P = 3.03x10 -11 , HCT P = 8.31x10 -9 ) were significantly associated with both HGB and HCT. Additional CpG sites were significantly associated with HCT ( PLXND1 cg22902177; P = 7.54x10 -11 and ARL1 cg23903357; P = 9.86x10 -11 ) and RDW ( CPNE2 cg09018739; P = 3.03x10 -22 ). These findings shed light on potential hematologic and CVD mechanisms in understudied populations. Future work will explore the role of neighboring SNPs in mediating observed methylation-trait associations, and replicate results in an additional multi-ethnic cohort.

Functional characterization of novel ABCB6 mutations and their clinical implications in familial pseudohyperkalemia.

Isolated familial pseudohyperkalemia is a dominant red cell trait characterized by cold-induced 'passive leak' of red cell potassium ions into plasma. The causative gene of this condition is ABCB6, which encodes an erythrocyte membrane ABC transporter protein bearing the Langereis blood group antigen system. In this study analyzing three new families, we report the first functional characterization of ABCB6 mutants, including the homozygous mutation V454A, heterozygous mutation R276W, and compound heterozygous mutations R276W and R723Q (in trans). All these mutations are annotated in public databases, suggesting that familial pseudohyperkalemia could be common in the general population. Indeed, we identified variant R276W in one of 327 random blood donors (0.3%). Four weeks' storage of heterozygous R276W blood cells resulted in massive loss of potassium compared to that from healthy control red blood cells. Moreover, measurement of cation flux demonstrated greater loss of potassium or rubidium ions from HEK-293 cells expressing ABCB6 mutants than from cells expressing wild-type ABCB6. The R276W/R723Q mutations elicited greater cellular potassium ion efflux than did the other mutants tested. In conclusion, ABCB6 missense mutations in red blood cells from subjects with familial pseudohyperkalemia show elevated potassium ion efflux. The prevalence of such individuals in the blood donor population is moderate. The fact that storage of blood from these subjects leads to significantly increased levels of potassium in the plasma could have serious clinical implications for neonates and infants receiving large-volume transfusions of whole blood. Genetic tests for familial pseudohyperkalemia could be added to blood donor pre-screening. Further study of ABCB6 function and trafficking could be informative for the study of other pathologies of red blood cell hydration.

Detection of Familial Pseudohyperkalemia Among Italian Blood Donors By Genetic Screening for the R276W Mutation in ABCB6

IntroductionIsolated Familial Pseudohyperkalemia (FP) is a dominant red cell trait characterized by cold-induced slow 'passive leak' of red cell K+ into plasma, first described in a large Scottish family from Edinburgh (Stewart GW, et al., 1979). Although in freshly obtained blood samples plasma [K+] was normal, it was increased when measured in blood stored at or below room temperature. This trait was accompanied by mild abnormalities of red cell shape.Functional gene mapping and sequencing analysis of the candidate genes within the 2q35-q36 critical interval in three multigenerational FP families with 20 affected individuals identified two novel heterozygous missense mutations in the ABCB6 gene that cosegregated with disease phenotype (Andolfo I. et al., 2013). The two genomic substitutions altered two adjacent nucleotides within codon 375 of ABCB6, a porphyrin transporter that in erythrocyte membranes bears the Langereis blood group antigen system (Krishnamurthy PC, et al., 2006; Helias V, et al., 2012).Recently, the ABCB6 mutation R723Q was found in two patients with FP (Bawazir W, et al.,2014). Of note, both patients presented as blood donors, and increased cold-induced potassium leak was demonstrated. The transfusion of pseudohyperkalemic blood has clinical implications especially for neonates and infants receiving large-volume RBC transfusions.In this study we analyzed one additional family and report the first functional characterization of an ABCB6 mutation, towards understanding the pathogenic mechanism of FP. Moreover, we screened an Italian blood donor population for the R276W variant of the ABCB6 gene.MethodsDNA was obtained for genetic analysis from affected and unaffected family members, after signed informed consent, according to the Declaration of Helsinki. The search for mutations was performed by direct sequencing of the ABCB6 gene. cDNAs encoding full-length wildtype ABCB6 were cloned into pcDNA3.1. Our patients' novel point mutation (c.826C>T, p.R276W) was introduced into pcDNA3.1-ABCB6 by site-directed mutagenesis. WT and mutant constructs were transfected into HEK-293 cells and the cells were maintained at 30°C for 72 hrs to evaluate the effects of reduced temperature. After transfection, the cells were incubated in a medium containing 86rubidium (86Rb+) as a surrogate for K+. 86Rb+ was determined in cell lysate, and K content of extracellular medium was determined by atomic absorption spectrometry.ResultsWe found the heterozygous mutation c.826G>T, p. R276W in an Irish family. This mutation is annotated in public databases as single nucleotide variants (SNVs), and is predicted by PolyPhen2 and SIFT to be damaging. Variant R276W showed a minor allele frequency (MAF) of 1.3:100 confirming that many patients with FP could be present in the blood donor population.R276W and previously identified ABCB6 variants R375Q and R375Wwere overexpressed in HEK-293 cells to characterize the functional properties of these variants. Expression of ABCB6 mutants showed no change in RNA or polypeptide levels. However, measurement of ouabain- and bumetanide-resistant net cation flux demonstrated a greater loss of cell K from mutant ABCB6-expressing cells than from WT ABCB6-expressing cells.The high allele frequency of ABCB6 variant R276W prompted a genetic screen of 327 blood donors. The variant was present in 0.3% (1/327) of the donor cohort, and this single subject with ABCB6 R276W exhibited slightly increased MCV and variably increased plasma K+ concentrations.Conclusions: Our findings demonstrate that missense mutations in ABCB6 lead to increased K+ efflux from RBCs in FP patients. Storage of FP blood can cause a significant increase in blood K+ levels, with especially serious clinical implications for neonates and infants receiving large-volume transfusions of whole blood. Furthermore, the prevalence of FP might be underestimated, since patients with FP can be asymptomatic and thus undetected in the donor population. Screening for the most frequent ABCB6 variation, R276W, confirmed that FP patients are present in the Italian blood donor population. In the future, genetic tests for FP could be added to blood donor prescreening to improve the quality and safety of donor units. DisclosuresNo relevant conflicts of interest to declare.

Missense mutations in the ABCB6 transporter cause dominant familialpseudohyperkalemia

Familial Pseudohyperkalemia (FP) is a dominant red cell trait characterized by increased serum [K(+)] in whole blood stored at or below room temperature, without additional hematological abnormalities. Functional gene mapping and sequencing analysis of the candidate genes within the 2q35-q36 critical interval identified-in 20 affected individuals among three multigenerational FP families-two novel heterozygous missense mutations in the ABCB6 gene that cosegregated with disease phenotype. The two genomic substitutions altered two adjacent nucleotides within codon 375 of ABCB6, a porphyrin transporter that, in erythrocyte membranes, bears the Langereis blood group antigen system. The ABCB6 R375Q mutation did not alter the levels of mRNA or protein, or protein localization in mature erythrocytes or erythroid precursor cells, but it is predicted to modestly alter protein structure. ABCB6 mRNA and protein levels increase during in vitro erythroid differentiation of CD34(+) erythroid precursors and the erythroleukemia cell lines HEL and K562. These data suggest that the two missense mutations in residue 375 of the ABCB6 polypeptide found in affected individuals of families with chromosome 2-linked FP could contribute to the red cell K(+) leak characteristic of this condition.

Missense Mutations in the ABCB6 Transporter Cause Dominant Familial Pseudohyperkalemia

AbstractAbstract 3184Isolated Familial Pseudohyperkalemia (FP) is a dominant red cell trait characterized by cold-induced slow ‘passive leak' of red cell K+ into plasma, first described in a large Scottish family from Edinburgh (Stewart GW, et al., 1979). Although in freshly obtained blood samples plasma [K+] was normal, it was increased when measured in blood stored at or below room temperature. This trait was unaccompanied by clinical symptoms or signs except for mild abnormalities of red cell shape. FP Lille was later described in a large Flemish kindred with morphologically normal red cells (Dagher G, et al., 1989; Vantyghem MC, et al., 1991). In this family, red cell K+ efflux measured in the presence of ouabain and bumetanide was normal at 37°C, but greatly increased at 22°C and 9°C. FP Lille mapped to 2q35-q36 (Carella M, et al., 2004), whereas FP Edinburgh mapped to 16q23-qter (Iolascon A, et al., 1999). Subsequently, asymptomatic cases FP Chiswick and FP Falkirk with remarkable increased MCV were reported (Haines PG, et al., 2001).Functional gene mapping and sequencing analysis of the candidate genes within the 2q35-q36 critical interval in three multigenerational FP families with 20 affected individuals identified two novel heterozygous missense mutations in the ABCB6 gene that cosegregated with disease phenotype. The two genomic substitutions altered two adjacent nucleotides within codon 375 of ABCB6, a porphyrin transporter that in erythrocyte membranes bears the Langereis blood group antigen system (Krishnamurthy PC, et al., 2006; Helias V, et al., 2012). Structural modeling predicts subtle changes in protein structure associated with either mutation.ABCB6 mRNA and protein levels increased during erythroid differentiation of CD34+ erythroid precursors (at 7 and 14 days of EPO induced differentiation), and of HEL and K562 erythroleukemia cells. However, the ABCB6 R375Q mutation altered neither levels of ABCB6 mRNA or protein, nor protein localization in mature erythrocytes or erythroid precursor cells. These data strongly suggest that missense mutations in residue 375 of the ABCB6 polypeptide either mediate the cold-induced K+ leak of chromosome 2-linked FP, or activate an independent, cold-induced cation permeability pathway of the red cell. Disclosures:No relevant conflicts of interest to declare.

Estimates of genetic and phenotypic parameters for production, haematological and gastrointestinal nematode-associated traits in Australian Angora goats

Genetic parameters for liveweight (LWT), greasy fleece weight (GFW), mean fibre diameter (MFD), standard deviation of MFD (MFD-s.d.), mean fibre curvature (CURVE) percentage of medullated (%MED) and kemp (%KEMP) fibres, faecal worm egg count (WEC), packed cell volume (PCV), mean corpuscular volume (MCV) mean corpuscular haemoglobin content (MCHC), circulating anti-nematode IgG (IgG) and counts of circulating eosinophils (EOS), lymphocytes (LYM), neutrophils (NEU), basophils (BASO) and monocytes (MONO) up to 18 months of age were estimated in Australian Angora goats (608 animals, 14 sires 3 years of birth). Measurements were made during a period of natural parasite challenge up to 5 months of age, or following artificial challenge with 10 000 infective larvae of Trichostrongylus colubriformis at 5.25 months of age. Year of birth had a significant impact on production and parasite-associated traits at all ages studied. Sex had a marked effect on production and erythrocyte traits. Birth type had no effect on any traits in animals older than 6 months. Maternal effects were not significant except for LWT at 3, 5 and 6 months and for IgG at 3 months. Most production traits were highly (LWT, GFW, MFD, %MED) or moderately (CURVE, MFD-s.d.) heritable (range 0.17–0.59) with only %KEMP having a low heritability (0.02–0.14). The heritability estimates (±s.e.) for CURVE are novel for goats and ranged from 0.18 ± 0.09 at first shearing to 0.44 ± 0.14 at third shearing. Heritability estimates were low for WEC (0.02–0.16) and for specific IgG during natural infection (0.14–0.15) but higher for IgG following artificial challenge with T. colubriformis (0.42 ± 0.13). Of the haematological variables NEU and all red cell traits were highly heritable (0.45–0.71), LYM and MONO were moderately to highly heritable (0.31–0.55), and EOS was weakly to moderately heritable (0.06–0.28). Strong phenotypic correlations existed between production traits. MFD was positively correlated with GFW and negatively correlated with CURVE, indicating that finer fibres have a higher crimp or wave count. WEC had consistent negative phenotypic correlations with PCV, LYM and EOS, and positive correlations with NEU. Correlations with IgG were positive up to 5 months and negative thereafter. Phenotypic correlations between WEC and LWT as well as with GFW and MFD were negative. Heritability estimates for production traits were generally consistent with other studies. Haematological and fibre curvature findings are completely novel for Angora goats. Estimates of heritability for WEC fell in mid range of published findings for other goat breeds, and these results suggest that there is some scope for breeding for worm resistance in Angoras but the response is likely to be slow.

A second locus mapping to 2q35-36 for familial pseudohyperkalaemia.

Familial pseudohyperkalaemia (FP) is a symptomless, dominantly inherited red cell trait, which shows a 'passive leak' of K+ cations into the plasma upon storage of blood at room temperature (or below). There are no haematological abnormalities. The loss of K+ is due to a change in the temperature dependence of the leak. The Scottish case initially described, FP Edinburgh, maps to 16q23-qter. Here we studied a large kindred of Flemish descent with FP, termed FP Lille, which was phenotypically identical to the Edinburgh FP. In FP Lille, however, the responsible locus mapped to 2q35-36, with a Lod score of 8.46 for marker D2S1338. We infer that FP Edinburgh and FP Lille, although they are phenocopies of one another, stem from two distinct loci, FP1 (16q23-qter) and FP2 (2q35-36), respectively. This duality hints at the possibility that the protein mediating the leak might be a heterodimer. No mutation was found in three plausibly candidate genes: the KCNE4 gene, the TUBA1 gene and a predicted gene located in genomic contig NT_005403.