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Ruhl AP, Jackson JM, Carhuas CJ, Niño de Rivera JG, Fay MP, Weinberg JB, Que LG, Ackerman HC. Association of alpha globin gene copy number with exhaled nitric oxide in a cross-sectional study of healthy Black adults. BMJ Open Respir Res 2023; 10:e001714. [PMID: 38123476 DOI: 10.1136/bmjresp-2023-001714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 11/14/2023] [Indexed: 12/23/2023] Open
Abstract
INTRODUCTION The genetic determinants of fractional exhalation of nitric oxide (FeNO), a marker of lung inflammation, are understudied in Black individuals. Alpha globin (HBA) restricts nitric oxide signalling in arterial endothelial cells via interactions with nitric oxide synthase; however, its role in regulating the release of NO from respiratory epithelium is less well understood. We hypothesised that an HBA gene deletion, common among Black individuals, would be associated with higher FeNO. METHODS Healthy Black adults were enrolled at four study sites in North Carolina from 2005 to 2008. FeNO was measured in triplicate using a nitric oxide analyzer. The -3.7 kb HBA gene deletion was genotyped using droplet digital PCR on genomic DNA. The association of FeNO with HBA copy number was evaluated using multivariable linear regression employing a linear effect of HBA copy number and adjusting for age, sex and serum immunoglobulin-E levels. Post-hoc analysis employing a recessive mode of inheritance was performed. RESULTS 895 individuals were in enrolled in the study and 720 consented for future genetic research; 643 had complete data and were included in this analysis. Median (25th, 75th) FeNO was 20 (13, 31) ppb. HBA genotypes were: 30 (4.7%) -a/-a, 197 (30.6%) -a/aa, 405 (63%) aa/aa and 8 (1.2%) aa/aaa. Subjects were 35% male with median age 20 (19, 22) years. Multivariable linear regression analysis revealed no association between FeNO and HBA copy number (β=-0.005 (95% CI -0.042 to 0.033), p=0.81). In the post-hoc sensitivity analysis, homozygosity for the HBA gene deletion was associated with higher FeNO (β=0.107 (95% CI 0.003 to 0.212); p=0.045). CONCLUSION We found no association between HBA copy number and FeNO using a prespecified additive genetic model. However, a post hoc recessive genetic model found FeNO to be higher among subjects homozygous for the HBA deletion.
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Affiliation(s)
- A Parker Ruhl
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
- Pulmonary Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Jarrett M Jackson
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - Carlos J Carhuas
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - Jessica G Niño de Rivera
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - Michael P Fay
- Biostatistics Research Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - J Brice Weinberg
- Department of Medicine and Division of Hematology, Duke University School of Medicine and Durham VA Medical Centers, Durham, North Carolina, USA
| | - Loretta G Que
- Department of Medicine and Division of Pulmonary, Allergy, and Critical Care Medicine, Duke University School of Medicine and Durham VA Medical Centers, Durham, North Carolina, USA
| | - Hans C Ackerman
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
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Alpha globin gene copy number and hypertension risk among Black Americans. PLoS One 2022; 17:e0271031. [PMID: 35834496 PMCID: PMC9282593 DOI: 10.1371/journal.pone.0271031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Accepted: 06/22/2022] [Indexed: 01/27/2023] Open
Abstract
BACKGROUND Alpha globin is expressed in the endothelial cells of human resistance arteries where it binds to endothelial nitric oxide synthase and limits release of the vasodilator nitric oxide. Genomic deletion of the alpha globin gene (HBA) is common among Black Americans and could lead to increased endothelial nitric oxide signaling and reduced risk of hypertension. METHODS Community-dwelling US adults aged 45 years or older were enrolled and examined from 2003 to 2007, followed by telephone every 6 months, and reexamined from 2013 to 2016. At both visits, trained personnel performed standardized, in-home blood pressure measurements and pill bottle review. Prevalent hypertension was defined as systolic blood pressure ≥ 140mmHg or diastolic blood pressure ≥ 90mmHg or anti-hypertensive medication use. Droplet digital PCR was used to determine HBA copy number. The associations of HBA copy number with prevalent hypertension, resistant hypertension, and incident hypertension were estimated using multivariable regression. RESULTS Among 9,684 Black participants, 7,439 (77%) had hypertension at baseline and 1,044 of those had treatment-resistant hypertension. 1,000 participants were not hypertensive at baseline and participated in a follow up visit; 517 (52%) developed hypertension over median 9.2 years follow-up. Increased HBA copy number was not associated with prevalent hypertension (PR = 1.00; 95%CI 0.98,1.02), resistant hypertension (PR = 0.95; 95%CI 0.86,1.05), or incident hypertension (RR = 0.96; 95%CI 0.86,1.07). CONCLUSIONS There were no associations between increased HBA copy number and risk of hypertension. These findings suggest that variation in alpha globin gene copy number does not modify the risk of hypertension among Black American adults.
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Ruhl AP, Jeffries N, Yang Y, Naik RP, Patki A, Pecker LH, Mott BT, Zakai NA, Winkler CA, Kopp JB, Lange LA, Irvin MR, Gutierrez OM, Cushman M, Ackerman HC. Alpha Globin Gene Copy Number Is Associated with Prevalent Chronic Kidney Disease and Incident End-Stage Kidney Disease among Black Americans. J Am Soc Nephrol 2022; 33:213-224. [PMID: 34706968 PMCID: PMC8763181 DOI: 10.1681/asn.2021050653] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Accepted: 10/05/2021] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND α-Globin is expressed in endothelial cells of resistance arteries, where it limits endothelial nitric oxide signaling and enhances α-adrenergic-mediated vasoconstriction. α-Globin gene (HBA) copy number is variable in people of African descent and other populations worldwide. Given the protective effect of nitric oxide in the kidney, we hypothesized that HBA copy number would be associated with kidney disease risk. METHODS Community-dwelling Black Americans aged ≥45 years old were enrolled in a national longitudinal cohort from 2003 through 2007. HBA copy number was measured using droplet digital PCR. The prevalence ratio (PR) of CKD and the relative risk (RR) of incident reduced eGFR were calculated using modified Poisson multivariable regression. The hazard ratio (HR) of incident ESKD was calculated using Cox proportional hazards multivariable regression. RESULTS Among 9908 participants, HBA copy number varied from 2 to 6. In analyses adjusted for demographic, clinical, and genetic risk factors, a one-copy increase in HBA was associated with 14% greater prevalence of CKD (PR, 1.14; 95% CI, 1.07 to 1.21; P<0.0001). While HBA copy number was not associated with incident reduced eGFR (RR, 1.06; 95% CI, 0.94 to 1.19; P=0.38), the hazard of incident ESKD was 32% higher for each additional copy of HBA (HR, 1.32; 95% CI, 1.09 to 1.61; P=0.005). CONCLUSIONS Increasing HBA copy number was associated with a greater prevalence of CKD and incidence of ESKD in a national longitudinal cohort of Black Americans.
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Affiliation(s)
- A. Parker Ruhl
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland,Pulmonary Branch, National Heart, Lung, and Blood Institute, Bethesda, Maryland
| | - Neal Jeffries
- Office of Biostatistics Research, National Heart, Lung, and Blood Institute, Bethesda, Maryland
| | - Yu Yang
- Division of Blood Diseases and Resources, National Heart, Lung, and Blood Institute, Rockville, Maryland
| | - Rakhi P. Naik
- Division of Hematology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Amit Patki
- Department of Biostatistics, University of Alabama at Birmingham, Birmingham, Alabama
| | - Lydia H. Pecker
- Division of Hematology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Bryan T. Mott
- University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | - Neil A. Zakai
- Department of Medicine, Larner College of Medicine at the University of Vermont, Burlington, Vermont,Department of Pathology & Laboratory Medicine, Larner College of Medicine at the University of Vermont, Burlington, Vermont
| | - Cheryl A. Winkler
- Basic Research Program, National Cancer Institute, Frederick National Laboratory for Cancer Research, Frederick, Maryland
| | - Jeffrey B. Kopp
- Kidney Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | - Leslie A. Lange
- Division of Biomedical Informatics and Personalized Medicine, Department of Medicine, University of Colorado, Denver, Colorado
| | - Marguerite R. Irvin
- Department of Epidemiology, University of Alabama at Birmingham School of Public Health, Birmingham, Alabama
| | - Orlando M. Gutierrez
- Department of Epidemiology, University of Alabama at Birmingham School of Public Health, Birmingham, Alabama,Department of Medicine, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | - Mary Cushman
- Department of Medicine, Larner College of Medicine at the University of Vermont, Burlington, Vermont,Department of Pathology & Laboratory Medicine, Larner College of Medicine at the University of Vermont, Burlington, Vermont
| | - Hans C. Ackerman
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland
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