Association among sickle cell trait, fitness, and cardiovascular risk factors in CARDIA

Sickle Cell Trait and Risk for Common Diseases: Evidence from the UK Biobank

BACKGROUND

Sickle cell trait is typically considered benign. Although evidence remains inconsistent, recent studies suggest that it is associated with several common diseases. We systematically assessed associations of sickle cell trait with reported diseases in a large population-based cohort.

METHODS

Study subjects were self-reported Blacks from the UK Biobank (UKB), a United Kingdom population-based cohort of subjects aged 40-69 years at recruitment in the United Kingdom. Sickle cell status was based on the International Classification of Diseases, Tenth Revision (ICD-10) or mutations in the HBB gene. Diagnoses of diseases were obtained from ICD-10 and self-reports. Associations of sickle cell trait and diseases were tested using logistic regression, adjusting for age at recruitment, sex, and genetic background (top 10 principal components).

RESULTS

Among the 8019 Blacks in the UKB, 699 (8.72%) were sickle cell trait carriers; the rate was significantly higher in females (9.74%) than males (7.48%), P = .0005. Sickle cell trait was under-diagnosed; most heterozygous hemoglobin subunit beta (HBB) gene Glu6Val carriers did not have a sickle cell trait ICD-10 record. Compared with non-sickle cell trait, sickle cell trait carriers had significantly increased risk for type 2 diabetes; odds ratio 1.38; 95% confidence interval, 1.12-1.68; P = .002. Sickle cell trait was also significantly associated with increased risk for renal diseases (rhabdomyolysis, end-stage renal disease, chronic kidney disease, renal papillary necrosis) and vascular diseases (hypertension, retinopathy, non-ischemic stroke), P < .05. While most of these diseases are complications/comorbidities of diabetes, their associations with sickle cell trait remained significant after adjusting for diabetes. Association with end-stage renal disease was stronger in subjects without diabetes, odds ratio 6.45; 95% confidence interval, 1.93-19.61; P = .001.

CONCLUSIONS

Sickle cell trait is significantly associated with increased risk for diabetes and diabetes-related complications/comorbidities.

Health services use by children identified as heterozygous hemoglobinopathy mutation carriers via newborn screening

Background

Newborn screening (NBS) for sickle cell disease incidentally identifies heterozygous carriers of hemoglobinopathy mutations. In Ontario, Canada, these carrier results are not routinely disclosed, presenting an opportunity to investigate the potential health implications of carrier status. We aimed to compare rates of health services use among children identified as carriers of hemoglobinopathy mutations and those who received negative NBS results.

Methods

Eligible children underwent NBS in Ontario from October 2006 to March 2010 and were identified as carriers or as screen-negative controls, matched to carriers 5:1 based on neighbourhood and timing of birth. We used health care administrative data to determine frequencies of inpatient hospitalizations, emergency department (ED) visits, and physician encounters through March 2012, using multivariable negative binomial regression to compare rates of service use in the two cohorts. We analyzed data from 4987 carriers and 24,935 controls.

Results

Adjusted incidence rate ratios (95% CI) for service use in carriers versus controls among children < 1 year of age were: 1.11 (1.06–1.17) for ED visits; 0.97 (0.89–1.06) for inpatient hospitalization; and 1.02 (1.00–1.04) for physician encounters. Among children ≥1 year of age, adjusted rate ratios were: 1.03 (0.98–1.07) for ED visits; 1.14 (1.03–1.25) for inpatient hospitalization and 0.92 (0.90–0.94) for physician encounters.

Conclusions

While we identified statistically significant differences in health services use among carriers of hemoglobinopathy mutations relative to controls, effect sizes were small and directions of association inconsistent across age groups and health service types. Our findings are consistent with the assumption that carrier status is likely benign in early childhood.

Preventive measures for the critical postexercise period in sickle cell trait and disease

The immediate postexercise/physical activity period is critical for sickle cell trait (SCT) carriers and disease (SCD) patients. Exercise-related blood acidosis is known to trigger the cascade of HbS deoxygenation and polymerization, leading to red blood cell sickling and subsequent complications. Unfortunately, two facts worsen exercise-related blood acidosis during the initial postexercise period: First, blood lactate and H⁺ concentrations continue to increase for several minutes after exercise completion, exacerbating blood acidosis. Second, blood lactate concentration remains elevated and pH altered for 20-45 min during inactivity after intense exercise, keeping acid/base balance disturbed for a long period after exercise. Therefore, the risk of complications (including vasoocclusive crises and even sudden death) persists and even worsens several minutes after intense exercise completion in SCT carriers or SCD patients. Light physical activity following intense exercise (namely, active recovery) may, by accelerating lactate removal and acid/base balance restoration, reduce the risk of complications. Scientific evidence suggests that light exercise at or below the first lactate threshold is an appropriate strategy.

Haematogenous osteoarticular infections in paediatric sickle cell trait patients: A reality in a tertiary centre in West Africa

BACKGROUND

Sickle cell trait (SCT) affects at least 5.2% of the world population, and it is considered asymptomatic by medical practitioners. There is a paucity of data regarding SCT paediatric patients and haematogenous osteoarticular infections (HOAIs). In our practice, some children with SCT presented HOAIs. This study aims to describe the pattern of HOAIs in children with SCT admitted in our unit.

MATERIALS AND METHODS

A single-centre retrospective study of medical records of SCT paediatric patients treated for HOAIs between January 2012 and June 2019 was performed. The data extracted were epidemiologic (gender, age at diagnosis, history of haemoglobinopathy and ethnic group), diagnostic (time to diagnosis, type of infection and fraction of haemoglobin S [HbS] at standard electrophoresis of Hb), germs and complications.

RESULTS

Among 149 patients with haemoglobinopathy treated for HOAIs, 52 have SCT. The prevalence of SCT patients was 34.9%. Thirty-nine (n = 39) records were retained for the study. The average age at diagnosis was 7.18 ± 4.59 years (7 months-15 years). The Malinké ethnic group was found in 22 (56.4%) cases. The mean HbS fraction was 37.2% ± 4.3% (30%-46%). Septic arthritis and osteoarthritis involved the hip in 11 cases, the shoulder in 4 and the knee in 2. Osteomyelitis was acute in 5 cases (11.1%) and chronic in 16 (35.5%). None of the patients has multifocal involvements. Bacterial identification was positive in 17 cases (37.8%). Staphylococcus aureus was involved in 9 cases (52.9%), and in one case, it was Mycobacterium tuberculosis. This patient has abscess of the psoas. No patient was infected by human immunodeficiency virus. The sequelae were joint destruction (n = 2), epiphysiodesis (n = 5) and retractile scars (n = 2).

CONCLUSION

Relatively infrequent in our daily practice, SCT patients present with HOAIs. These infections had characteristics that are not very different from the series of the literature.

Effects of -3.7α Deletion and Sickle-Cell Trait on Ventilatory and Hemodynamic Responses to Maximum Exercise in Young Saudi Females

Introduction

Hemoglobinopathies are common disorders in Saudi Arabia and have an impact on the general health of the affected individuals. The current study aimed to find out the effects of the presence of α 3.7 kb rightward deletion or sickle-cell trait (SCT) on ventilatory and hemodynamic parameters of maximum exercise testing in young Saudi women.

Methods

In a cross-sectional study, 75 randomly selected female students from different colleges were tested for VO_2max using a COSMED system for maximum exercise testing. Blood parameters and globin genotyping were determined.

Results

Hemoglobin genetic studies revealed 28 of the students had 3.7 α-globin deletion only (^−3.7α₂/α₁α₂), five had SCT, and 42 had normal α-globin (α₁α₂/α₁α₂ and no HbS) and were considered the control group. Subjects with ^−3.7α₂/α₁α₂ showed significantly lower VO_2max and higher resting systolic blood pressure, while SCT carriers showed no difference in regard to ventilatory parameters, but had higher post-exercise systolic blood pressure than controls.

Conclusion

It is concluded that individuals with 3.7 α-globin deletion might have lower fitness capacity, as demonstrated by lower VO_2max, which might explain the general lower VO_2max in the young women of this population. Furthermore, increments in resting systolic and posteexercise systolic blood pressure in 3.7 α-globin deletion and SCT, respectively, might indicate a future risk of cardiovascular diseases and require attention and extensive studies.

The current state of sickle cell trait: implications for reproductive and genetic counseling

Sickle cell trait (SCT) is unique among the carrier states that are identified during newborn screening. Unlike other heterozygous states for rare recessive diseases, SCT is exceedingly prevalent throughout regions of the world, making sickle cell disease one of the most common monogenetic diseases worldwide. Because of this high frequency, reproductive counseling is of paramount importance. In addition, unlike other carrier states, SCT seems to be a risk factor for several clinical complications, such as extreme exertional injury, chronic kidney disease, and venous thromboembolism. Increasing knowledge about these clinical outcomes can help inform genetic counseling recommendations. Expanding research and clinical efforts are needed to ensure that the promises of modern and precision medicine can be delivered to the millions of SCT carriers and their children.

Association Between Sickle Cell Trait With Selected Chronic Medical Conditions in U.S. Service Members

Introduction

Sickle cell trait (SCT), the heterozygous carrier state for hemoglobin S, is present in an estimated 1.6% of all newborns and 7.3% in black individuals in the USA. SCT has long been considered a benign condition with anticipated normal life expectancy and no increased risk for chronic diseases. The medical literature is inconclusive on the potential association between SCT and chronic medical conditions (CMC) including chronic kidney disease, venous thromboembolism, and stroke. Studies addressing these questions are lacking particularly in non-Black young adults.

Materials and Methods

We conducted a retrospective cohort study among U.S. active duty, enlisted, service members who entered from 1992 to 2012 using existing Department of Defense (DoD Military Healthcare System databases). SCT positive subjects (1,323) were matched by demographic characteristics to SCT negative subjects (3,136) and followed through 2013 for CMC that included deep vein thrombosis, diabetes mellitus and hematologic, pulmonary, and renal conditions.

Results

The rate of developing any of the included CMC was higher for those with SCT (incidence rate ratio = 1.71 95% CI 1.61-1.81) compared with those who were SCT negative and their healthcare utilization rate for any of CMC studied was higher for SCT positive compared with negative individuals (URR = 2.45 95% CI 2.41-2.50), with the highest rate ratios observed for hematologic and renal conditions. SCT positive compared with negative individuals were more likely to have encounter diagnoses of sickle cell disease and diabetes Type II and were less likely to have encounter diagnoses of other hemoglobinopathies and diabetes type I.

Conclusion

SCT in these racially diverse, young adults increased both the incidence of and healthcare utilization for thromboembolism, diabetes mellitus type II, sickle cell disease, pulmonary, and chronic renal conditions. These findings suggest that clinicians treating young adults with SCT should exercise heightened surveillance for these CMC to ensure both early diagnosis and access to treatments.

Effect of Previous Exposure to Malaria on Blood Pressure in Kilifi, Kenya: A Mendelian Randomization Study

Background Malaria exposure in childhood may contribute to high blood pressure ( BP ) in adults. We used sickle cell trait ( SCT ) and α+thalassemia, genetic variants conferring partial protection against malaria, as tools to test this hypothesis. Methods and Results Study sites were Kilifi, Kenya, which has malaria transmission, and Nairobi, Kenya, and Jackson, Mississippi, where there is no malaria transmission. The primary outcome was 24-hour systolic BP. Prevalent hypertension, diagnosed using European Society of Hypertension thresholds was a secondary outcome. We performed regression analyses adjusting for age, sex, and estimated glomerular filtration rate. We studied 1127 participants in Kilifi, 516 in Nairobi, and 651 in Jackson. SCT frequency was 21% in Kilifi, 16% in Nairobi, and 9% in Jackson. SCT was associated with -2.4 (95% CI , -4.7 to -0.2) mm Hg lower 24-hour systolic BP in Kilifi but had no effect in Nairobi/Jackson. The effect of SCT in Kilifi was limited to 30- to 59-year-old participants, among whom it was associated with -6.1 mm Hg ( CI , -10.5 to -1.8) lower 24-hour systolic BP. In pooled analysis allowing interaction by site, the effect of SCT on 24-hour systolic BP in Kilifi was -3.5 mm Hg ( CI , -6.9 to -0.1), increasing to -5.2 mm Hg ( CI , -9.5 to -0.9) when replacing estimated glomerular filtration rate with urine albumin to creatinine ratio as a covariate. In Kilifi, the prevalence ratio for hypertension was 0.86 ( CI , 0.76-0.98) for SCT and 0.89 ( CI , 0.80-0.99) for α+thalassemia. Conclusions Lifelong malaria protection is associated with lower BP in Kilifi. Confirmation of this finding at other sites and elucidating the mechanisms involved may yield new preventive and therapeutic targets.

The current state of sickle cell trait: implications for reproductive and genetic counseling

Sickle cell trait (SCT) is unique among the carrier states that are identified during newborn screening. Unlike other heterozygous states for rare recessive diseases, SCT is exceedingly prevalent throughout regions of the world, making sickle cell disease one of the most common monogenetic diseases worldwide. Because of this high frequency, reproductive counseling is of paramount importance. In addition, unlike other carrier states, SCT seems to be a risk factor for several clinical complications, such as extreme exertional injury, chronic kidney disease, and venous thromboembolism. Increasing knowledge about these clinical outcomes can help inform genetic counseling recommendations. Expanding research and clinical efforts are needed to ensure that the promises of modern and precision medicine can be delivered to the millions of SCT carriers and their children.

Balancing exercise risk and benefits: lessons learned from sickle cell trait and sickle cell anemia

Development of exercise guidelines for individuals with sickle cell trait (SCT) and sickle cell anemia (SCA) is hampered by the need to weigh the benefits against risks of exercise in these populations. In SCT, concern for exercise collapse associated with sickle cell trait has resulted in controversial screening of student athletes for SCT. In SCA, there exists unsubstantiated concerns that high-intensity exercise may result in pain and other complications. In both, finding the "right dose" of exercise remains a challenge for patients and their providers. Despite assumptions that factors predisposing to adverse events from high-intensity exercise overlap in SCT and SCA, the issues that frame our understanding of exercise-related harms in both are distinct. This review will compare issues that affect the risk-benefit balance of exercise in SCT and SCA through these key questions: (1) What is the evidence that high-intensity exercise is associated with harm? (2) What are the pathophysiologic mechanisms that could predispose to harm? (3) What are the preventive strategies that may reduce risk? and (4) Why do we need to consider the benefits of exercise in this debate? Addressing these knowledge gaps is essential for developing an evidence-based exercise prescription for these patient populations.

Clinical Outcomes Associated With Sickle Cell Trait: A Systematic Review

Background

Although sickle cell trait (SCT) is largely a benign carrier state, it may increase risk for certain clinical outcomes.

Purpose

To evaluate associations between SCT and clinical outcomes in children and adults.

Data Sources

English-language searches of PubMed, CINAHL, the Cochrane Library, Current Contents Connect, Scopus, and Embase (1 January 1970 to 30 June 2018) and bibliographies of review articles.

Study Selection

Observational controlled studies (published in English) in children or adults that examined an association between SCT and any of 24 clinical outcomes specified a priori in the following 6 categories: exertion-related injury; renal, vascular, pediatric, and surgery- or trauma-related outcomes; and overall mortality.

Data Extraction

A single reviewer extracted study data, which was checked by another; 2 reviewers independently assessed study quality; and strength of evidence was assessed by consensus.

Data Synthesis

Of 7083 screened studies, 41 met inclusion criteria. High-strength evidence supported a positive association between SCT and risk for pulmonary embolism, proteinuria, and chronic kidney disease. Moderate-strength evidence supported a positive association between SCT and exertional rhabdomyolysis and a null association between SCT and deep venous thrombosis, heart failure or cardiomyopathy, stroke, and pediatric height or weight. Absolute risks for thromboembolism and rhabdomyolysis were small. For the remaining 15 clinical outcomes, data were insufficient or strength of evidence was low.

Limitation

Publication bias was possible, and high-quality evidence was scant.

Conclusion

Sickle cell trait is a risk factor for a few adverse health outcomes, such as pulmonary embolism, kidney disease, and exertional rhabdomyolysis, but does not seem to be associated with such complications as heart failure and stroke. Insufficient data or low-strength evidence exists for most speculated complications of SCT.

Primary Funding Source

National Human Genome Research Institute.

Cardiovascular Health in African Americans: A Scientific Statement From the American Heart Association

BACKGROUND AND PURPOSE

Population-wide reductions in cardiovascular disease incidence and mortality have not been shared equally by African Americans. The burden of cardiovascular disease in the African American community remains high and is a primary cause of disparities in life expectancy between African Americans and whites. The objectives of the present scientific statement are to describe cardiovascular health in African Americans and to highlight unique considerations for disease prevention and management.

METHOD

The primary sources of information were identified with PubMed/Medline and online sources from the Centers for Disease Control and Prevention.

RESULTS

The higher prevalence of traditional cardiovascular risk factors (eg, hypertension, diabetes mellitus, obesity, and atherosclerotic cardiovascular risk) underlies the relatively earlier age of onset of cardiovascular diseases among African Americans. Hypertension in particular is highly prevalent among African Americans and contributes directly to the notable disparities in stroke, heart failure, and peripheral artery disease among African Americans. Despite the availability of effective pharmacotherapies and indications for some tailored pharmacotherapies for African Americans (eg, heart failure medications), disease management is less effective among African Americans, yielding higher mortality. Explanations for these persistent disparities in cardiovascular disease are multifactorial and span from the individual level to the social environment.

CONCLUSIONS

The strategies needed to promote equity in the cardiovascular health of African Americans require input from a broad set of stakeholders, including clinicians and researchers from across multiple disciplines.

Characterization of a mouse model of sickle cell trait: parallels to human trait and a novel finding of cutaneous sensitization

Sickle cell trait (SCT) has classically been categorized as a benign condition except in rare cases or upon exposure to severe physical conditions. However, several lines of evidence indicate that individuals with SCT are not always asymptomatic, and additional physiological changes and risks may remain unexplored. Here, we utilized mice harbouring one copy of normal human β globin and one copy of sickle human β globin as a model of SCT to assess haematological, histopathological and somatosensory outcomes. We observed that SCT mice displayed renal and hepatic vascular congestion after exposure to hypoxia. Further, we observed that SCT mice displayed increased cold aversion as well as mechanical and heat sensitivity, though to a lesser degree than homozygous sickle cell disease mice. Notably, mechanical hypersensitivity increased following hypoxia and reoxygenation. Overall our findings suggest that SCT is not entirely benign, and further assessment of pain and cutaneous sensitization is warranted both in animal models and in clinical populations.

Sickle cell trait knowledge and health literacy in caregivers who receive in-person sickle cell trait education

BACKGROUND

Despite universal screening that detects sickle cell trait (SCT) in infancy, only 16% of Americans with SCT know their status. To increase SCT status awareness, effective education for patients and their families is needed. The objective of this study was to assess caregivers' SCT knowledge before and after an in-person SCT education session.

METHODS

A trained educator provides in-person SCT education to caregivers of referred infants with SCT at Nationwide Children's Hospital. From August 2015 to July 2016, primarily English-speaking caregivers of infants with hemoglobin S-trait were recruited and completed a health literacy assessment and a SCT knowledge assessment (SCTKA) before and after receiving education. Caregivers repeated the SCTKA again after ≥6 months, if they could be contacted.

RESULTS

Thirty-eight (38.1%) percent of 113 caregivers had high SCTKA scores (≥75%) before education but 90.3% achieved high scores after education. Caregivers with low SCTKA scores after education had significantly lower health literacy (P = 0.029) and baseline SCTKA scores (P = 0.003) compared to those with higher scores after education. At ≥6 months, caregivers' scores were significantly higher (P = 0.014) than baseline, but only 73.3% scored ≥75%.

CONCLUSION

Our results suggest that caregivers' baseline SCT knowledge is low, improves with in-person education but may decline with time. Caregivers who do not achieve high SCT knowledge after education had lower health literacy and baseline knowledge. Future studies should determine if adapting in-person education to caregivers' health literacy and knowledge levels results in high and sustained SCT knowledge among all caregivers and more individuals who know their SCT status.