Clinical implications of sickle-cell trait and glucose-6-phosphate dehydrogenase deficiency in hospitalized black male patients

Sickle cell trait does not cause "sickle cell crisis" leading to exertion-related death: a systematic review

ABSTRACT

Globally, an estimated 300 million individuals have sickle cell trait (SCT), the carrier state for sickle cell disease (SCD). Although SCD is associated with increased morbidity and shortened life span, SCT has a life span comparable with that of the general population. However, "sickle cell crisis" has been used as a cause of death for decedents with SCT in reports of exertion-related death in athletes, military personnel, and individuals in police custody. To appraise this practice, the American Society of Hematology convened an expert panel of hematologists and forensic pathologists to conduct a systematic review of the literature relating to the occurrence of sickle cell pain crises and exertion-related mortality in people with SCT. Multiple bibliographic databases were searched with controlled vocabulary and keywords related to "sickle cell trait," "vaso-occlusive pain," and "death," yielding 18 of 1474 citations. Independent pairs of reviewers selected studies and extracted data. We found no studies comparing uncomplicated acute pain crises in individuals with SCT and SCD. Additionally, no study was identified to support the occurrence of acute vaso-occlusive pain crises in individuals with SCT. Furthermore, this systematic review did not identify any evidence to support an association between SCT and sudden unexplained death in the absence of exertion-related rhabdomyolysis. We conclude that there are no data to support the diagnosis of acute vaso-occlusive sickle cell crisis as a cause of death in SCT, nor does the available evidence support the use of SCT as a cause of exertion-related death without rhabdomyolysis.

A positive correlation between mutated gene of sickle cell anemia and glucose-6-phosphate dehydrogenase among gond tribes of Chhattisgarh, India

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymopathy affecting millions of individuals worldwide. It is believed that the prevalence of G6PD deficiency in different ethnic populations increases its association with other pathological conditions especially sickle cell anemia (SCA), as they both are well-known adaptations against malaria. Thus, the present study aims to determine the frequency of G6PD deficiency among SCA patients and the association between them in the tribal community (Gond) of Chhattisgarh, India.

METHOD

A total of 810 samples from three different age groups i.e., 10-20, 21-30, and 31-40 years were collected from the tribal community (Gond) of Kabirdham district of Chhattisgarh. The frequency of SCA was determined by a slide test followed by cellulose acetate paper electrophoresis and G6PD deficiency by methemoglobin reduction test. Glutathione-S-Transferase (GST) gene polymorphism in sickle celled individuals and variant analysis in G6PD deficient individuals were analyzed by RT-PCR.

RESULTS

The frequency of SCA and G6PD deficiency was reported at 9.75% and 17.16% respectively and a high degree of positive correlation between SCA and G6PD deficiency was also found (HbSS-G6PD deficient: r = 0.84, p = .356; HbAS-G6PD deficient: r = 0.89, p = .345). Results of the GST gene revealed that GSTM1 and GSTT1 genes are present in almost all sickled individuals while GSTP1 and GSTP1a exist in the mutated form in a maximum percentage of individuals. G6PD variant analysis also showed that 70% and 60% of individuals have mutated Mahidol and Union variants respectively, while none of the individuals have mutated Chinese variants.

CONCLUSION

A high degree of correlation between SCA and G6PD was reported among Gond tribes of Chhattisgarh, India with a high degree of mutated GSTP1, GSTP1a, Mahidol, and Union variants. The study makes it possible to take specific preventive measures concerning the medication of anti-oxidizing drugs.

Blood rheology and vascular function in sickle cell trait and sickle cell disease: From pathophysiological mechanisms to clinical usefulness

Sickle cell disease (SCD) is an autosomal recessive disorder. Although the molecular mechanisms at the origin of SCD have been well characterized, its clinical expression is highly variable. SCD is characterized by blood rheological abnormalities, increased inflammation and oxidative stress, and vascular dysfunction. Individuals with only one copy of the mutated β-globin gene have sickle cell trait (SCT) and are usually asymptomatic. The first part of this review focuses on the biological responses of SCT carriers during exercise and on the effects of combined SCT and diabetes on vascular function, several biomarkers and clinical complications. The second part of the review focuses on SCD and shows that the magnitude of red blood cell (RBC) rheological alterations is highly variable from one patient to another, and this variability reflects the clinical and hematological variability: patients with the less deformable RBCs have high hemolytic rate and severe anemia, and are prone to develop leg ulcers, priapism, cerebral vasculopathy, glomerulopathy or pulmonary hypertension. In contrast, SCD patients characterized by the presence of more deformable RBCs (but still rigid) are less anemic and may exhibit increased blood viscosity, which increases the risk for vaso-occlusive events. Several genetic and cellular factors may modulate RBC deformability in SCD: co-existence of α-thalassemia, fetal hemoglobin level, oxidative stress, the presence of residual mitochondria into mature RBCs, the activity of various non-selective cationic ion channels, etc. The last part of this review presents the effects of hydroxyurea and exercise training on RBC rheology and other biomarkers in SCD.

Management of the Sickle Cell Trait: An Opinion by Expert Panel Members

The number of individuals with the sickle cell trait exceeds 300 million worldwide, making sickle cell disease one of the most common monogenetic diseases globally. Because of the high frequency of sickle cell disease, reproductive counseling is of crucial importance. In addition, unlike other carrier states, Sickle Cell Trait (SCT) seems to be a risk factor for several clinical complications, such as extreme exertional injury, chronic kidney disease, and complications during pregnancy and surgery. This expert panel believes that increasing knowledge about these clinical manifestations and their prevention and management can be a useful tool for all healthcare providers involved in this issue.

Epidemiology and prevention of venous thromboembolism

Venous thromboembolism, that consists of the interrelated conditions deep-vein thrombosis and pulmonary embolism, is an under-appreciated vascular disease. In Western regions, approximately 1 in 12 individuals will be diagnosed with venous thromboembolism in their lifetime. Rates of venous thromboembolism are lower in Asia, but data from other regions are sparse. Numerous risk factors for venous thromboembolism have been identified, which can be classified as acute or subacute triggers (provoking factors that increase the risk of venous thromboembolism) and basal or acquired risk factors (which can be modifiable or static). Approximately 20% of individuals who have a venous thromboembolism event die within 1 year (although often from the provoking condition), and complications are common among survivors. Fortunately, opportunities exist for primordial prevention (prevention of the development of underlying risk factors), primary prevention (management of risk factors among individuals at high risk of the condition) and secondary prevention (prevention of recurrent events) of venous thromboembolism. In this Review, we describe the epidemiology of venous thromboembolism, including the incidence, risk factors, outcomes and opportunities for prevention. Meaningful health disparities exist in both the incidence and outcomes of venous thromboembolism. We also discuss these disparities as well as opportunities to reduce them.

Etiology of Persistent Microalbuminuria in Nigeria (P_MICRO study): protocol and study design

BACKGROUND

Microalbuminuria is an independent risk factor for cardiovascular and kidney disease and a predictor of end organ damage, both in the general population and in persons with HIV (PWH). Microalbuminuria is also an important risk factor for mortality in PWH treated with antiretroviral therapy (ART). In the ongoing Renal Risk Reduction (R3) study in Nigeria, we identified a high prevalence of microalbuminuria confirmed by two measurements 4-8 weeks apart in ART-experienced, virologically suppressed PWH. Although Stage 1 or 2 hypertension and exposure to potentially nephrotoxic antiretroviral medications were common in R3 participants, other traditional risk factors for albuminuria and kidney disease, including diabetes, APOL1 high-risk genotype, and smoking were rare. Co-infection with endemic pathogens may also be significant contributors to albuminuria, but co-infections were not evaluated in the R3 study population.

METHODS

In Aim 1, we will cross-sectionally compare the prevalence of albuminuria and established kidney disease risk factors in a cohort of PWH to age- and sex-matched HIV-negative adults presenting for routine care at the Aminu Kano Teaching Hospital in Kano, Nigeria. We will leverage stored specimens from 2500 R3 participants and enroll an additional 500 PLWH recently initiated on ART (≤ 24 months) and 750 age- and sex-matched HIV-negative adults to determine the contribution of HIV, hypertension, and other comorbid medical conditions to prevalent albuminuria. In Aim 2, we will follow a cohort of 1000 HIV-positive, ART-treated and 500 HIV-negative normoalbuminuric adults for 30 months to evaluate the incidence and predictors of albuminuria.

DISCUSSION

The findings from this study will support the development of interventions to prevent or address microalbuminuria in PWH to reduce kidney and cardiovascular morbidity and mortality. Such interventions might include more intensive monitoring and treatment of traditional risk factors, the provision of renin-angiotensin aldosterone system or sodium-glucose cotransporter-2 inhibitors, consideration of changes in ART regimen, and screening and treatment for relevant co-infections.

The nephropathy of sickle cell trait and sickle cell disease

Sickle cell syndromes, including sickle cell disease (SCD) and sickle cell trait, are associated with multiple kidney abnormalities. Young patients with SCD have elevated effective renal plasma flow and glomerular filtration rates, which decrease to normal ranges in young adulthood and subnormal levels with advancing age. The pathophysiology of SCD-related nephropathy is multifactorial - oxidative stress, hyperfiltration and glomerular hypertension are all contributing factors. Albuminuria, which is an early clinical manifestation of glomerular damage, is common in individuals with SCD. Kidney function declines more rapidly in individuals with SCD than in those with sickle cell trait or in healthy individuals. Multiple genetic modifiers, including APOL1, HMOX1, HBA1 and HBA2 variants are also implicated in the development and progression of SCD-related nephropathy. Chronic kidney disease and rapid decline in estimated glomerular filtration rate are associated with increased mortality in adults with SCD. Renin-angiotensin-aldosterone system inhibitors are the standard of care treatment for albuminuria in SCD, despite a lack of controlled studies demonstrating their long-term efficacy. Multiple studies of novel therapeutic agents are ongoing, and patients with SCD and kidney failure should be evaluated for kidney transplantation. Given the high prevalence and severe consequences of kidney disease, additional studies are needed to elucidate the pathophysiology, natural history and treatment of SCD-related nephropathy.

Gene therapy for sickle cell disease: where we are now?

The landscape of sickle cell disease (SCD) treatment continues to evolve rapidly, with new disease-modifying therapies in development and potentially curative options on the horizon. Until recently, allogeneic stem cell transplant has been the only proven cure for SCD. Gene therapy is rising to the forefront of the discussion as a potentially curative or highly disease- modifying option for abating the complications of the disease. Understanding the different types of gene therapy in use, the differences in their end points, and their potential risks and benefits will be key to optimizing the long-term use of this therapy.

Challenging the dogma of the healthy heterozygote: Implications for newborn screening policies and practices

Heterozygous (carrier) status for an autosomal recessive condition is traditionally considered to lack significance for an individual's health, but this assumption has been challenged by a growing body of evidence. Carriers of several autosomal recessive disorders and some X-linked diseases are potentially at risk for the pathology manifest in homozygotes. This minireview provides an overview of the literature regarding health risks to carriers of two common autosomal recessive conditions on the Recommended Uniform Screening Panel: sickle cell disease [sickle cell trait (SCT)] and cystic fibrosis (CF). We also consider and comment on bioethical and policy implications for newborn blood screening (NBS). Health risks for heterozygotes, while relatively low for individuals, are often influenced by intrinsic (e.g., other genomic variants or co-morbidities) and extrinsic (environmental) factors, which present opportunities for personalized genomic medicine and risk counseling. They create a special challenge, however, for developing screening/follow-up policies and for genetic counseling, particularly after identification and reporting of heterozygote status through NBS. Although more research is needed, this minireview of the SCT and CF literature to date leads us to propose that blanket terms such as "healthy heterozygotes" or "unaffected carriers" should be superseded in communications about NBS results, in favor of a more nuanced paradigm of setting expectations for health outcomes with "genotype-to-risk." In the molecular era of NBS, it remains clear that public health needs to become better prepared for the full range of applied genetics.

NCAA Division I American football players with sickle cell trait have altered hematological responses and hydration status

Sickle cell trait (SCT) is a risk factor of collapse and sudden death in athletes. We conducted a longitudinal study to determine the hematological responses and hydration status in NCAA Division I American football players with SCT. The study took place over 2 years with 6 SCT and 6 position-matched controls (CON) in year 1; and 4 SCT and 4 CON in year 2. In year 2, three of the four SCT players were recruited and re-enrolled with new position-matched controls (total sample data = 10 SCT and 10 CON). Blood samples were taken at three visits: pre-camp, post-camp, and post-season to examine hemoglobin variants, complete blood counts, and chemistry panel 26. Hydration status was assessed by measuring body weight change, urine specific gravity, and urine and sweat electrolyte concentrations during the pre-season training camp. All SCT players were confirmed to have SCT (HbS = 37.9 ± 2.4%) and had greater red cell distribution width (RDW) compared to CON across all visits. Serum uric acid was higher in SCT (7.3 ± 1.0 mg/dL) compared to CON (6.1 ± 0.6 mg/dL; p = 0.001). Furthermore, serum creatine kinase levels were greater in SCT (1617.0 ± 1034.8 IU/L) at pre-camp compared to CON (1037.4 ± 602.8 IU/L; p = 0.03). SCT players exhibited lower pre- and post-practice urine electrolytes and urine specific gravity (SCT pre: 1.019 ± 0.005 vs. CON pre: 1.026 ± 0.008 p < 0.001; SCT post: 1.020 ± 0.005 vs. CON post: 1.030 ± 0.008 p < 0.01), whereas sweat sodium concentrations were higher in SCT players (55.4 ± 13.6 mmol/L) compared to CON (45.5 ± 10.6 mmol/L; p < 0.001). Given the evidence, greater uric acid and CPK levels in SCT players compared to CON may be an early indicator of altered kidney function and muscle damage, which could be added into NCAA guidelines for surveillance among SCT players. Consistent education and reinforcement of the importance of adequate fluid balance during exercise are critical for both SCT and CON players.

Thirty-year risk of ischemic stroke in individuals with sickle cell trait and modification by chronic kidney disease: The atherosclerosis risk in communities (ARIC) study

Sickle cell trait (SCT) has been associated with hypercoagulability, chronic kidney disease (CKD), and ischemic stroke. Whether concomitant CKD modifies long-term ischemic stroke risk in individuals with SCT is uncertain. We analyzed data from 3602 genotyped black adults (female = 62%, mean baseline age = 54 years) who were followed for a median 26 years by the Atherosclerosis Risk in Communities Study. Ischemic stroke was verified by physician review. Associations between SCT and ischemic stroke were analyzed using repeat-events Cox regression, adjusted for potential confounders. SCT was identified in 236 (7%) participants, who more often had CKD at baseline than noncarriers (18% vs 13%, P = .02). Among those with CKD, elevated factor VII activity was more prevalent with SCT genotype (36% vs 22%; P = .05). From 1987-2017, 555 ischemic strokes occurred in 436 individuals. The overall hazard ratio of ischemic stroke associated with SCT was 1.31 (95% CI: 0.95-1.80) and was stronger in participants with concomitant CKD (HR = 2.18; 95% CI: 1.16-4.12) than those without CKD (HR = 1.09; 95% CI: 0.74-1.61); P for interaction = .04. The hazard ratio of composite ischemic stroke and/or death associated with SCT was 1.20 (95% CI: 1.01-1.42) overall, 1.44 (95% CI: 1.002-2.07) among those with CKD, and 1.15 (95% CI: 0.94-1.39) among those without CKD; P for interaction = .18. The long-term risk of ischemic stroke associated with SCT relative to noncarrier genotype appears to be modified by concomitant CKD.

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 of Sickle Cell Trait With Ischemic Stroke Among African Americans: A Meta-analysis

Importance

African Americans and individuals of African ancestry have a higher risk of stroke compared with non-Hispanic white individuals. Identifying the source of this disparity could provide an opportunity for clinical stroke risk stratification and more targeted therapy. Whether sickle cell trait (SCT) is an indicator of increased risk of ischemic stroke among African Americans is still unclear.

Objective

To examine whether SCT is associated with a higher risk of incident ischemic stroke among African Americans.

Design, Setting, and Participants

This meta-analysis assessed the association of SCT with the risk of incident ischemic stroke. Four large, prospective, population-based studies with African American cohorts were assessed: Jackson Heart Study (September 1, 2005, through December 31, 2012), Multi-Ethnic Study of Atherosclerosis (July 1, 2002, through December 31, 2012), Reasons for Geographic and Racial Differences in Stroke (January 1, 2003, through December 31, 2014), and Women's Health Initiative (October 1, 1998, through December 31, 2012). Using a Cox proportional hazards regression model adjusted for major stroke risk factors, this study estimated the hazard ratio for incident ischemic stroke associated with SCT. Data analysis was performed from July 10, 2016, to February 2, 2017.

Interventions or Exposures

Participants' SCT status determined by polymerase chain reaction assay genotyping or a combination of whole-exome sequencing and imputation.

Main Outcomes and Measures

Incident ischemic stroke.

Results

This meta-analysis included 19 464 African American individuals (1520 with SCT, 17 944 without SCT, and 620 with ischemic stroke) from 4 studies, with a mean (SD) age of 60.0 (13.0) years (5257 [27.0%] men and 14 207 [73.0%] women). No differences were found in the distribution of risk factors for ischemic stroke comparing participants with and those without SCT at study visit 1 in each cohort. The crude incidence of ischemic stroke was 2.9 per 1000 person-years (95% CI, 2.2-4.0 per 1000 person-years) among those with SCT and 3.2 per 1000 person-years (95% CI, 2.7-3.8 per 1000 person-years) among those without SCT. After stroke risk factors were adjusted for, the hazard ratio of incident ischemic stroke independently associated with SCT in the meta-analysis of all 4 cohorts was 0.80 (95% CI, 0.47-1.35; P = .82). The results of the meta-analysis were similar to those of individual cohorts, in which the results were also similar.

Conclusions and Relevance

Sickle cell trait may not be associated with incidence of ischemic stroke among African Americans. The results of this study suggest performing a more thorough clinical evaluation of a stroke patient with SCT rather than assuming that SCT is the etiologic factor for the stroke.

Sickle cell trait and risk of cognitive impairment in African-Americans: The REGARDS cohort

BACKGROUND

Sickle cell anemia may be associated with cognitive dysfunction, and some complications of sickle cell anemia might affect those with sickle cell trait (SCT), so we hypothesized that SCT is a risk factor for cognitive impairment.

METHODS

The Reasons for Geographic and Racial Differences in Stroke (REGARDS) study enrolled a national cohort of 30,239 white and black Americans from 2003 to 7, who are followed every 6 months. Baseline and annual global cognitive function testing used the Six-Item Screener (SIS), a validated instrument (scores range 0-6; ≤ 4 indicates cognitive impairment). Participants with baseline cognitive impairment and whites were excluded. Logistic regression was used to calculate the association of SCT with incident cognitive impairment, adjusted for risk factors. Linear mixed models assessed multivariable-adjusted change in test scores on a biennially administered 3-test battery measuring learning, memory, and semantic and phonemic fluency.

FINDINGS

Among 7743 participants followed for a median of 7·1 years, 85 of 583 participants with SCT (14·6%) developed incident cognitive impairment compared to 902 of 7160 (12·6%) without SCT. In univariate analysis, the odds ratio (OR) of incident cognitive impairment was 1·18 (95% CI: 0·93, 1·51) for those with SCT vs. those without. Adjustment did not impact the OR. There was no difference in change on 3-test battery scores by SCT status (all p > 0·11).

INTERPRETATION

In this prospective cohort study of black Americans, SCT was not associated with incident cognitive impairment or decline in test scores of learning, memory and executive function.

FUNDING

National Institutes of Health, American Society of Hematology.

Prevalence of glucose-6-phosphate dehydrogenase deficiency in Cameroonian blood donors

Objective

Deficiency in G6PD is the most common enzymopathy worldwide. It is frequently found in individuals of African descent in whom it can lead to hemolytic crises triggered by the use of certain antimalarial medications and infection. The prevalence of G6PD deficiency and its contribution to morbidity in West Africa is under-studied. To understand the prevalence of glucose-6-phosphate dehydrogenase (G6PD) deficiency in West African blood donors.

Results

We evaluated the G6PD status and infectious disease screening tests of 1001 adult male Cameroonian blood donors (mean age 31.7 ± 9.8 years). The prevalence of G6PD deficiency was 7.9%. There was no difference in levels of hemoglobin or ABO subtype between those who were G6PD-normal compared to those that were deficient. Interestingly, G6PD-normal vs. deficient blood donors were less likely to have screened positive for hepatitis C virus (p = 0.02) and rapid plasma reagin (indicative of syphilis, p = 0.03). There was no significant difference in hepatitis B sAg, HIV-1, or HIV-2 reactivity between those with vs. without G6PD sufficiency. These data suggest that G6PD deficiency is common among West African male blood donors and may be associated with specific infectious disease exposure.

The Association Between Sickle Cell Trait in U.S. Service Members with Deployment, Length of Service, and Mortality, 1992-2012

Introduction

Sickle cell trait (SCT) affects an estimated 5.02% of non-Hispanic blacks, 1.08% of Hispanics, and 0.1% of Whites in the U.S. military. Policies for SCT screening and occupational restrictions vary by service. Population-based studies of SCT with quantification of military-relevant outcomes are lacking.

Methods

The study design was a retrospective cohort of 15,081 SCT-positive versus 60,320 SCT-negative U.S. active duty personnel enlisted from 1992 to 2012 and followed through 2013. Military-relevant outcome included number and days of deployment, length of service, and cause of death.

Results

SCT-positive versus SCT-negative service members experienced more deployments (p < 0.01) and longer number of days deployed for all services, especially the Army (p < 0.001). The median length of service was longer for SCT-positive service members stratified by service and by gender (p < 0.05). The adjusted risk of length of service greater than 5 yr by SCT status was 1.37 (95% confidence interval 1.31-1.43) with greater than a three-fold higher risk in the Navy and Air Force compared with the Army. Crude mortality rate was not significantly different by SCT status, although deaths due to suicide, self-directed violence, and other non-specific causes were more common in SCT-positive service members.

Conclusion

We found that SCT-positive service members deployed more frequently, for greater lengths of time, and remained in service longer. No significant difference in crude mortality ratio was discovered. Additional research on military-relevant outcomes and a cost-effectiveness analysis of SCT screening practices are needed to inform evidence-based SCT enlistment policies.

Multifactorial Origin of Exertional Rhabdomyolysis, Recurrent Hematuria, and Episodic Pain in a Service Member with Sickle Cell Trait

Individuals with Sickle Cell Trait (SCT), generally considered a benign carrier state of hemoglobin S (HbAS), are thought to be at risk for exertional rhabdomyolysis and hematuria, conditions that can also be caused by various other acquired and inherited factors. We report an SCT positive service member with an exertional rhabdomyolysis event, recurrent hematuria with transient proteinuria, and episodic burning pain in the lower extremities. Clinical and genetic studies revealed the multifactorial nature of his complex phenotype. The service member was taking prescription medications known to be associated with exertional rhabdomyolysis. He carried a pathogenic mutation, NPHS2 p.V260E, reported in nephropathy and a new variant p.R838Q in SCN11A, a gene involved in familial episodic pain syndrome. Results suggest that drug-to-drug interactions coupled with the stress of exercise, coinheritance of HbAS and NPHS2 p.V260E, and p. R838Q in SCN11A contributed to exertional rhabdomyolysis, recurrent hematuria with proteinuria, and episodic pain, respectively. This case underscores the importance of comprehensive clinical and genetic evaluations to identify underlying causes of health complications reported in SCT individuals.

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.

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.

Risk of Exertional Heat Illnesses Associated with Sickle Cell Trait in U.S. Military

Introduction

A number of studies have found an association between sickle cell trait (SCT) and exertional heat illnesses (EHIs) including heat stroke, a potentially fatal condition. The strength of this association varied across studies, limiting the ability to quantify potential benefits of SCT-screening policies for competitive athletics and military service members. We determined the relative rate and attributable risk of developing EHI associated with being SCT positive and the EHI health care utilization.

Methods

We conducted a retrospective cohort study among U.S. enlisted, active duty service members during 1992-2012 from the Department of Defense Military Healthcare System databases. All 15,081 SCT-positive individuals and a sample of 60,320 from those considered SCT negative were followed through 2013 for EHI outcomes ranging from mild heat illness to heat stroke.

Results

The adjusted hazard ratio for EHI in SCT-positive compared with SCT-negative individuals was 1.24 (95% confidence interval 1.06, 1.45). Risk factors for EHI included age over 30 yr at enlistment, female gender, Marine Corps, combat occupations, and enlistment between April and June. An estimated 216 Department of Defense enlistees (95% confidence interval: 147, 370) would need to be screened to identify and potentially prevent one case of EHI. The attributable risk of EHI due to SCT was 33% (95% confidence interval 19, 45%).

Conclusion

Our findings suggest that SCT screening will identify approximately a third of SCT individuals at risk for EHI, but does not provide definitive evidence for universal compared with selective (e.g., occupational based) in military enlistees. A cost-effectiveness analysis is needed for policy makers to assess the overall value of universal SCT screening to prevent morbidity and mortality in both the military and the collegiate athletic populations.

Sickle Cell Trait and Sudden Death

Sickle cell trait has long been considered a benign condition but continues to be the leading cause of death in young African Americans in military basic training and civilian organized sports. There continues to be a great deal of controversy surrounding sickle cell trait and its association with exercise-related morbidity and sudden death. Even though sickle cell trait has a high prevalence among African Americans, many clinicians believe the potential adverse consequences should have been mitigated by actions such as universal screening in the USA at birth for sickle hemoglobin, National Collegiate Athletic Association (NCAA) rule changes, and changes in the US Military boot camp system. Sudden death due to periods of extreme physical exertion continues to occur in individuals with sickle cell trait.

Review and drug therapy implications of glucose-6-phosphate dehydrogenase deficiency

PURPOSE

The pathophysiology, diagnosis, and medication-use implications of glucose-6-phosphate dehydrogenase (G6PD) deficiency, the most common enzyme deficiency in humans, are reviewed.

SUMMARY

Originally identified as favism in patients who experienced hemolysis after ingestion of fava beans, G6PD deficiency results from an X-linked chromosomal mutation that leads to reduced activity of the enzyme responsible for the final step of the pentose phosphate pathway, through which reduced nicotinamide adenine dinucleotide phosphate required for protection of cells from oxidative stress is produced. G6PD deficiency affects about 400 million people worldwide. Diagnosis of G6PD can be made through detection of enzymatic activity (by spectrophotometric testing, fluorescence testing, or formazan-based spot testing) or molecular analysis to detect known mutations of the gene encoding G6PD. Most individuals with G6PD deficiency are asymptomatic throughout life. Symptoms of acute hemolysis associated with G6PD deficiency include anemia, fatigue, back or abdominal pain, jaundice, and hemoglobinuria. The most common precipitators of oxidative stress and hemolysis in G6PD deficiency include medication use and infection.

CONCLUSION

G6PD deficiency should be considered in patients who experience acute hemolysis after exposure to known oxidative medications, infection, or ingestion of fava beans. A diagnosis of G6PD deficiency is most often made through enzymatic activity detection, but molecular analysis may be required in females heterozygous for the disorder. When clinically feasible, rasburicase, primaquine, dapsone, pegloticase, and methylene blue should not be used until a G6PD diagnostic test has been performed.

The spectrum of sickle hemoglobin-related nephropathy: from sickle cell disease to sickle trait

INTRODUCTION

Renal dysfunction is among the most common complication of sickle cell disease (SCD), from hyposthenuria in children to progression to overt chronic kidney disease (CKD) in young adults. Emerging evidence now suggests that sickle hemoglobin-related nephropathy extends to individuals with sickle cell trait (SCT). Areas covered: This review will highlight the pathophysiology, epidemiology, and management recommendations for sickle hemoglobin-related nephropathy in both SCD and SCT. In addition, it will focus on the major demographic and genetic modifiers of renal disease in sickling hemoglobinopathies. Expert commentary: Studies have elucidated the course of renal disease in SCD; however, the scope and age of onset of renal dysfunction in SCT has yet to be determined. In SCD, several modifiers of renal disease - such as α-thalassemia, hemoglobin F, APOL1 and HMOX1 - have been described and provide an opportunity for a precision medicine approach to risk stratify patients who may benefit from early intervention. Extrapolating from this literature may also provide insight into the modifiers of renal disease in SCT. Further studies are needed to determine the optimal treatment for sickle hemoglobin-related nephropathy.

Renal Medullary Carcinoma: Establishing Standards in Practice

Although renal medullary carcinoma (RMC) is a rare subtype of kidney cancer, it is particularly devastating in that it is nearly uniformly lethal. No established guidelines exist for the diagnosis and management of RMC. In April 2016, a panel of experts developed clinical guidelines on the basis of a literature review and consensus statements. The goal was to propose recommendations for standardized diagnostic and management approaches and to establish an international clinical registry and biorepository for RMC. Published data are limited to case reports and small retrospective reviews. The RMC Working Group prepared recommendations to inform providers and patients faced with a low level of medical evidence. The diagnosis of RMC should be considered in all patients younger than 50 years with poorly differentiated carcinoma that arises from the renal medulla. These patients should be tested for sickle cell hemoglobinopathies, and if positive, SMARCB1/INI1 loss should be confirmed by immunohistochemistry. The majority of patients with RMC are diagnosed with metastatic disease. Upfront radical nephrectomy should be considered in patients with good performance status and low metastatic burden or after response to systemic therapy. Currently, cytotoxic, platinum-based chemotherapy provides the best, albeit brief, palliative clinical benefit. Vascular endothelial growth factor-directed therapies and mammalian target of rapamycin inhibitors are ineffective in RMC as monotherapy. Therapeutic trials of novel agents are now available for RMC, and every effort should be made to enroll patients in clinical studies.

Venous thromboembolism in adults screened for sickle cell trait: a population-based cohort study with nested case-control analysis

OBJECTIVE

To determine whether sickle cell carriers ('sickle cell trait') have an increased risk of venous thromboembolism (VTE).

DESIGN

Cohort study with nested case-control analysis.

SETTING

General population with data from 609 UK general practices in the Clinical Practice Research Datalink (CPRD).

PARTICIPANTS

All individuals registered with a CPRD general practice between 1998 and 2013, with a medical record of screening for sickle cell between 18 and 75 years of age.

MAIN OUTCOMES MEASURES

Incidence of VTE per 10 000 person-years (PY) among sickle cell carriers and non-carriers; and adjusted OR for VTE among sickle cell carriers compared with non-carriers.

RESULTS

We included 30 424 individuals screened for sickle cell, with a follow-up time of 179 503 PY, identifying 55 VTEs in 6758 sickle cell carriers and 125 VTEs in 23 666 non-carriers. VTE incidence among sickle cell carriers (14.9/10 000 PY; 95% CI 11.4 to 19.4) was significantly higher than non-carriers (8.8/10 000 PY; 95% CI 7.4 to 10.4). Restricting analysis to confirmed non-carriers was non-significant, but performed on a small sample. In the case-control analysis (180 cases matched to 1775 controls by age and gender), sickle cell carriers remained at increased risk of VTE after adjusting for body mass index, pregnancy, smoking status and ethnicity (OR 1.78, 95% CI 1.18 to 2.69, p=0.006), with the greatest risk for pulmonary embolism (PE) (OR 2.27, 95% CI 1.17 to 4.39, p=0.011).

CONCLUSIONS

Although absolute numbers are small, in a general population screened for sickle cell, carriers have a higher incidence and risk of VTE, particularly PE, than non-carriers. Clinicians should be aware of this elevated risk in the clinical care of sickle cell carriers, or when discussing carrier screening, and explicitly attend to modifiable risk factors for VTE in these individuals. More complete primary care coding of carrier status could improve analysis.

Glucose-6-Phosphate Dehydrogenase Deficiency and Physical and Mental Health until Adolescence

Background

To examine the association of glucose-6-phosphate dehydrogenase (G6PD) deficiency with adolescent physical and mental health, as effects of G6PD deficiency on health are rarely reported.

Methods

In a population-representative Chinese birth cohort: “Children of 1997” (n = 8,327), we estimated the adjusted associations of G6PD deficiency with growth using generalized estimating equations, with pubertal onset using interval censored regression, with hospitalization using Cox proportional hazards regression and with size, blood pressure, pubertal maturation and mental health using linear regression with multiple imputation and inverse probability weighting.

Results

Among 5,520 screened adolescents (66% follow-up), 4.8% boys and 0.5% girls had G6PD deficiency. G6PD-deficiency was not associated with birth weight-for-gestational age or length/height gain into adolescence, but was associated with lower childhood body mass index (BMI) gain (-0.38 z-score, 95% confidence interval (CI) -0.57, -0.20), adjusted for sex and parental education, and later onset of pubic hair development (time ratio = 1.029, 95% CI 1.007, 1.050). G6PD deficiency was not associated with blood pressure, height, BMI or mental health in adolescence, nor with serious infectious morbidity until adolescence.

Conclusions

G6PD deficient adolescents had broadly similar physical and mental health indicators, but transiently lower BMI gain and later pubic hair development, whose long-term implications warrant investigation.

Sickle Cell Trait from a Metabolic, Renal, and Vascular Perspective: Linking History, Knowledge, and Health

Sickle cell trait (SCT) is at the intersection of genetics, social policy, and medicine. SCT occurs in three-hundred million people worldwide and in approximately 8 % of African-Americans. There has been great debate about the influence of SCT on health. Yet data exist, albeit controversial, which suggest that SCT is associated with metabolic derangements that can lead to sudden death after vigorous physical activity, renal dysfunction, thromboembolic events, and stroke. In addition, it has even been postulated that SCT might enhance the vascular complications of diabetes. This review focuses on (a) the scientific breakthroughs that led to the discovery of hemoglobin S, sickle cell disease, and SCT, (b) the history of screening programs in the United States, (c) the incidence and etiology of exercise-related sudden death in military personnel and athletes with SCT, and (d) the data examining the potential chronic disease consequences of SCT from a metabolic, renal, and vascular perspective.

Prevalence of α(+)-Thalassemia in the Scheduled Tribe and Scheduled Caste Populations of Damoh District in Madhya Pradesh, Central India

This study was carried out to ascertain the allelic frequency of α(+)-thalassemia (α(+)-thal) in Scheduled caste and scheduled tribe populations of the Damoh district of Madhya Pradesh, India. Random blood samples of Scheduled tribe (267) and Scheduled caste (168), considering the family as a sampling unit, were analyzed for the presence of the -α(3.7) (rightward) (NG_000006.1: g.34164_37967del3804) and -α(4.2) (leftward) (AF221717) deletions. α(+)-Thal was significantly higher in the Scheduled tribals (77.9%) as compared to the scheduled caste population (9.0%). About 58.0% scheduled tribals carried at least one chromosome with the -α(3.7) deletion and 20.0% scheduled tribals carried the -α(4.2) deletion. Frequency for the -α(3.7) allele was 0.487 in the scheduled tribal populations in comparison to 0.021 in scheduled castes. Allelic frequency for -α(4.2) was 0.103 and 0.024, respectively, in the above communities. No Hardy-Weinberg equilibrium for α-thal gene (p < 0.05) was detected in the tribal population, indicating the presence of selection pressures in favor of α-thal mutation and adaptation.

Renal medullary carcinoma and sickle cell trait: A systematic review

Sickle cell trait (SCT) carries a small risk of renal medullary carcinoma (RMC). We conducted a systematic literature review and reported new four RMC cases (total N = 217). Eighty eight percent had SCT and 8% had sickle cell disease; 50% were children. Males had 2.4× risk than females. Isolated hematuria or in combination with abdominal or flank pain was the presenting sign in 66% cases. Tumor-related mortality was 95%. Four non-metastatic patients were long-term disease-free survivors. Although risk appears to be very low, individuals with SCT should be informed about the low risk of RMC with the hope of early diagnosis. Hematuria should prompt immediate investigation.

Coagulation activation in sickle cell trait: an exploratory study

Recent epidemiologic data suggest that sickle cell trait (HbAS; AS) is a risk factor for venous thromboembolism. We conducted an exploratory study of healthy subjects with AS under baseline conditions to determine whether a chronic basal hyperactivation of coagulation exists, and if so, what mechanism(s) contribute to this state. Eighteen healthy AS individuals were compared to 22 African-American controls with a normal haemoglobin profile (HbAA; AA) and 17 patients with sickle cell disease (HbSS; SS). Plasma thrombin-antithrombin complexes and D-dimer levels were elevated in AS relative to AA patients (P = 0·0385 and P = 0·017, respectively), and as expected, were much higher in SSversusAA (P < 0·0001 for both). Thrombin generation in platelet poor plasma was indistinguishable between AA and AS subjects, whereas a paradoxical decrease in endogenous thrombin potential was observed in SS (P ≤ 0·0001). Whole blood tissue factor was elevated in SS compared to AA (P = 0·005), but did not differ between AA and AS. Plasma microparticle tissue factor activity was non-significantly elevated in AS (P = 0·051), but was clearly elevated in SS patients (P = 0·004) when compared to AA controls. Further studies in larger cohorts of subjects with sickle cell trait are needed to confirm the results of this preliminary investigation.

Mechanical differences of sickle cell trait (SCT) and normal red blood cells

Sickle cell trait (SCT) is a condition in which an individual inherits one sickle hemoglobin gene (HbS) and one normal beta hemoglobin gene (HbA). It has been hypothesized that under extreme physical stress, the compromised mechanical properties of the red blood cells (RBCs) may be the underlying mechanism of clinical complications of sickle cell trait individuals. However, whether sickle cell trait (SCT) should be treated as physiologically normal remains controversial. In this work, the mechanical properties (i.e., shear modulus and viscosity) of individual RBCs were quantified using a microsystem capable of precisely controlling the oxygen level of RBCs' microenvironment. Individual RBCs were deformed under shear stress. After the release of shear stress, the dynamic cell recovery process was captured and analyzed to extract the mechanical properties of single RBCs. The results demonstrate that RBCs from sickle cell trait individuals are inherently stiffer and more viscous than normal RBCs from healthy donors, but oxygen level variations do not alter their mechanical properties or morphology.

Negative health implications of sickle cell trait in high income countries: from the football field to the laboratory

Worldwide, sickle cell trait is a highly prevalent gene carrier state. While generally a benign condition with a normal life expectancy, it is becoming increasingly clear that the sickle trait is associated with certain adverse outcomes. This article will focus on three of these outcomes, namely exertional rhabdomyolysis and sudden death, chronic renal dysfunction, and venous thromboembolism. In each case, the epidemiological evidence for the association is reviewed, together with the existing data on potential underlying mechanisms. Because newborn screening programmes for sickle cell anaemia also identify those with sickle cell trait, it is imperative that further studies determine what, if any, preventive measures can be taken to reduce the burden of these uncommon but potentially morbid complications in affected individuals.

Sickle cell disease and venous thromboembolism in pregnancy and the puerperium

Recent data strongly suggest an increased risk of venous thromboembolism in subjects with sickle cell disease and to a lesser extent, sickle cell trait. However, most studies have been retrospective, case-control or cross-sectional based on data obtained from administrative databases. More data from adequately powered prospective studies that include matched controls are needed to definitely establish the link between venous thromboembolism during pregnancy and sickle hemoglobin disorders. Similarly, there remains a need for properly designed randomized control trials to establish the safety of various hormonal contraceptive methods in women with sickle cell disorders.

Sickle cell trait diagnosis: clinical and social implications

The sickle hemoglobin (HbS) point mutation has independently undergone evolutionary selection at least five times in the world because of its overwhelming malarial protective effects in the heterozygous state. In 1949, homozygous Hb S or sickle cell disease (SCD) became the first inherited condition identified at the molecular level; however, since then, both SCD and heterozygous Hb S, sickle cell trait (SCT), have endured a long and complicated history. Hasty adoption of early mass screening programs for SCD, recent implementation of targeted screening mandates for SCT in athletics, and concerns about stigmatization have evoked considerable controversy regarding research and policy decisions for SCT. Although SCT is a largely protective condition in the context of malaria, clinical sequelae, such as exercise-related injury, renal complications, and venous thromboembolism can occur in affected carriers. The historical background of SCD and SCT has provided lessons about how research should be conducted in the modern era to minimize stigmatization, optimize study conclusions, and inform genetic counseling and policy decisions for SCT.

Prospective study of sickle cell trait and venous thromboembolism incidence

BACKGROUND

Sickle cell trait may increase risk of venous thromboembolism, but this is not fully established.

OBJECTIVES

We sought to determine the association of sickle cell trait with deep vein thrombosis and pulmonary embolism.

METHODS

Middle-aged African Americans participating in a prospective, population-based cohort investigation, the Atherosclerosis Risk in Communities Study, were followed from 1987 through 2011 for incident hospitalized pulmonary embolism (n = 111) or isolated deep vein thrombosis (n = 138), verified by physician review of medical records. Sickle cell trait (heterozygosity for hemoglobin S, n = 268) was compared with no sickle cell trait (n = 3748).

RESULTS

Over a median of 22 years of follow-up, 249 participants had an incident venous thromboembolism. The hazard ratio of venous thromboembolism was 1.50 (95% confidence interval [CI] 0.96-2.36) for participants with vs. without sickle cell trait, after adjustment for age, sex, ancestry, hormone replacement therapy (women), body mass index, diabetes, and estimated glomerular filtration rate. This hazard ratio was 2.05 (95% CI 1.12-3.76) for pulmonary embolism and 1.15 (95% CI 0.58-2.27) for deep vein thrombosis without pulmonary embolism.

CONCLUSIONS

Sickle cell trait in African Americans carries a 2-fold increased risk of pulmonary embolism but does not elevate deep vein thrombosis risk. Because neonatal screening for sickle hemoglobin is being conducted in the United States, consideration should be paid to the increased pulmonary embolism risk of individuals with sickle cell trait.

Association of sickle cell trait with chronic kidney disease and albuminuria in African Americans

IMPORTANCE

The association between sickle cell trait (SCT) and chronic kidney disease (CKD) is uncertain.

OBJECTIVE

To describe the relationship between SCT and CKD and albuminuria in self-identified African Americans.

DESIGN, SETTING, AND PARTICIPANTS

Using 5 large, prospective, US population-based studies (the Atherosclerosis Risk in Communities Study [ARIC, 1987-2013; n = 3402], Jackson Heart Study [JHS, 2000-2012; n = 2105], Coronary Artery Risk Development in Young Adults [CARDIA, 1985-2006; n = 848], Multi-Ethnic Study of Atherosclerosis [MESA, 2000-2012; n = 1620], and Women's Health Initiative [WHI, 1993-2012; n = 8000]), we evaluated 15,975 self-identified African Americans (1248 participants with SCT [SCT carriers] and 14,727 participants without SCT [noncarriers]).

MAIN OUTCOMES AND MEASURES

Primary outcomes were CKD (defined as an estimated glomerular filtration rate [eGFR] of <60 mL/min/1.73 m2 at baseline or follow-up), incident CKD, albuminuria (defined as a spot urine albumin:creatinine ratio of >30 mg/g or albumin excretion rate >30 mg/24 hours), and decline in eGFR (defined as a decrease of >3 mL/min/1.73 m2 per year). Effect sizes were calculated separately for each cohort and were subsequently meta-analyzed using a random-effects model.

RESULTS

A total of 2233 individuals (239 of 1247 SCT carriers [19.2%] vs 1994 of 14,722 noncarriers [13.5%]) had CKD, 1298 (140 of 675 SCT carriers [20.7%] vs 1158 of 8481 noncarriers [13.7%]) experienced incident CKD, 1719 (150 of 665 SCT carriers [22.6%] vs 1569 of 8249 noncarriers [19.0%]) experienced decline in eGFR, and 1322 (154 of 485 SCT carriers [31.8%] vs 1168 of 5947 noncarriers [19.6%]) had albuminuria during the study period. Individuals with SCT had an increased risk of CKD (odds ratio [OR], 1.57 [95% CI, 1.34-1.84]; absolute risk difference [ARD], 7.6% [95% CI, 4.7%-10.8%]), incident CKD (OR, 1.79 [95% CI, 1.45-2.20]; ARD, 8.5% [95% CI, 5.1%-12.3%]), and decline in eGFR (OR, 1.32 [95% CI, 1.07-1.61]; ARD, 6.1% [95% CI, 1.4%-13.0%]) compared with noncarriers. Sickle cell trait was also associated with albuminuria (OR, 1.86 [95% CI, 1.49-2.31]; ARD, 12.6% [95% CI, 7.7%-17.7%]).

CONCLUSIONS AND RELEVANCE

Among African Americans in these cohorts, the presence of SCT was associated with an increased risk of CKD, decline in eGFR, and albuminuria, compared with noncarriers. These findings suggest that SCT may be associated with the higher risk of kidney disease in African Americans.

Sickle cell trait: not as benign as once thought

We describe a case of renal papillary necrosis in a middle-aged female with sickle cell trait who presented with gross hematuria. We wish to highlight this case for several reasons. Sickle cell trait is often viewed as a benign condition despite the fact that it is associated with significant morbidity such as renal papillary necrosis and renal medullary carcinoma. Appropriate evaluation needs to be undertaken to promptly diagnose renal papillary necrosis and differentiate it from renal medullary carcinoma as this can result in deadly consequences for patients. CT urography has emerged as a diagnostic study to evaluate hematuria in such patients. We review the pathophysiology, diagnosis, and management of renal papillary necrosis in patients with sickle cell trait.

Sickle cell trait and incident ischemic stroke in the Atherosclerosis Risk in Communities study

BACKGROUND AND PURPOSE

Numerous case reports describe stroke in individuals with sickle cell trait (SCT) in the absence of traditional risk factors for cerebrovascular disease. To date, no prospective epidemiological studies have investigated this association.

METHODS

A population-based sample of blacks (n=3497; mean age=54 years; female=62%) was followed from 1987 to 2011 in the Atherosclerosis Risk in Communities (ARIC) study, contributing a total of 65 371 person-years. Hazard ratios and incidence rate differences for ischemic stroke were estimated, contrasting SCT to homozygous hemoglobin A. Models were adjusted for age, sex, smoking, diabetes mellitus, hypertension, total cholesterol, atrial fibrillation, and coronary heart disease.

RESULTS

SCT was identified in 223 (6.4%) participants. During a median follow-up of 22 years, 401 subjects experienced incident stroke (89% ischemic). Incident ischemic stroke was more frequent among those with SCT (13%) than those with homozygous hemoglobin A (10%). SCT was associated with an ischemic stroke hazard ratio of 1.4 (1.0-2.0) and an incidence rate difference amounting to 1.9 (0.4-3.8) extra strokes per 1000 person-years.

CONCLUSIONS

We observed an increased risk of ischemic stroke in blacks with SCT. Further investigation of the incidence and pathophysiology of stroke in patients with SCT is warranted.

A population survey of the glucose-6-phosphate dehydrogenase (G6PD) 563C>T (Mediterranean) mutation in Afghanistan

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common inherited enzyme defect and an important problem in areas with Plasmodium vivax infection because of the risk of haemolysis following administration of primaquine to treat the liver forms of the parasite. We undertook a genotypic survey of 713 male individuals across nine provinces of Afghanistan in which malaria is found, four in the north and five in the east. RFLP typing at nucleotide position 563 detected 40 individuals with the Mediterranean mutation 563C>T, an overall prevalence of 5.6%. This varied according to self-reported ethnicity, with prevalence in the Pashtun/Pashai group of 33/369 (8.9%) compared to 7/344 individuals in the rest of the population (2.0%; p<0.001, Chi-squared test). Multivariate analysis of ethnicity and geographical location indicated an adjusted odds ratio of 3.50 (95% CI 1.36-9.02) for the Pashtun/Pashai group, while location showed only a trend towards higher prevalence in eastern provinces (adjusted odds ratio = 1.73, 0.73-4.13). Testing of known polymorphic markers (1311C>T in exon 11, and C93T in intron XI) in a subset of 82 individuals wild-type at C563 revealed a mixture of 3 haplotypes in the background population and was consistent with data from the 1000 Genomes Project and published studies. By comparison individuals with G6PD deficiency showed a highly skewed haplotype distribution, with 95% showing the CT haplotype, a finding consistent with relatively recent appearance and positive selection of the Mediterranean variant in Afghanistan. Overall, the data confirm that the Mediterranean variant of G6PD is common in many ethnic groups in Afghanistan, indicating that screening for G6PD deficiency is required in all individuals before radical treatment of P. vivax with primaquine.

Sickle trait in African-American hemodialysis patients and higher erythropoiesis-stimulating agent dose

African Americans require higher doses of erythropoiesis-stimulating agents (ESAs) during dialysis to manage anemia, but the influence of sickle cell trait and other hemoglobinopathy traits on anemia in dialysis patients has not been adequately evaluated. We performed a cross-sectional study of a large cohort of adult African-American hemodialysis patients in the United States to determine the prevalence of hemoglobinopathy traits and quantify their influence on ESA dosing. Laboratory and clinical data were obtained over 6 months in 2011. Among 5319 African-American patients, 542 (10.2%) patients had sickle cell trait, and 129 (2.4%) patients had hemoglobin C trait; no other hemoglobinopathy traits were present. Sickle cell trait was more common in this cohort than the general African-American population (10.2% versus 6.5%-8.7%, respectively, P<0.05). Among 5002 patients (10.3% sickle cell trait and 2.4% hemoglobin C trait) receiving ESAs, demographic and clinical variables were similar across groups, with achieved hemoglobin levels being nearly identical. Patients with hemoglobinopathy traits received higher median doses of ESA than patients with normal hemoglobin (4737.4 versus 4364.1 units/treatment, respectively, P=0.02). In multivariable analyses, hemoglobinopathy traits associated with 13.2% more ESA per treatment (P=0.001). Within subgroups, sickle cell trait patients received 13.2% (P=0.003) higher dose and hemoglobin C trait patients exhibited a similar difference (12.9%, P=0.12). Sensitivity analyses using weight-based dosing definitions and separate logistic regression models showed comparable associations. Our findings suggest that the presence of sickle cell trait and hemoglobin C trait may explain, at least in part, prior observations of greater ESA doses administered to African-American dialysis patients relative to Caucasian patients.

The risk of potential thromboembolic, renal and cardiac complications of sickle cell trait

Many complications of sickle cell trait have been well-established, but associations with additional disease states remain controversial. We conducted a retrospective cohort study to examine the frequency of receiving a diagnosis of thromboembolism, pulmonary embolism (PE), ischemic stroke, renal disease (acute, chronic), coronary artery disease (CAD) and congestive heart failure (CHF) in patients with sickle cell trait. A total of 13,964 adult African Americans registered in the Kaiser Permanente Northern California (KPNC) health system (Oakland, CA, USA), were included based on laboratory and diagnostic code data for the years 1995-2008: 2642 with sickle cell trait, 11,183 with normal hemoglobin (Hb) and 139 with sickle cell disease. Disease outcomes were obtained from coded diagnoses. The adjusted relative risk of PE and chronic kidney disease in sickle cell trait patients compared to patients with normal Hb were 1.37 [95% confidence interval (CI) 1.07-1.75] and 1.13 (95% CI 1.03-1.23), respectively. There were no other significant differences in the outcomes for sickle cell trait patients compared to patients with normal Hb.

Glucose-6-phosphate dehydrogenase deficiency in transfusion medicine: the unknown risks

The hallmark of glucose-6-phosphate dehydrogenase (G6PD) deficiency is red blood cell (RBC) destruction in response to oxidative stress. Patients requiring RBC transfusions may simultaneously receive oxidative medications or have concurrent infections, both of which can induce haemolysis in G6PD-deficient RBCs. Although it is not routine practice to screen healthy blood donors for G6PD deficiency, case reports identified transfusion of G6PD-deficient RBCs as causing haemolysis and other adverse events. In addition, some patient populations may be more at risk for complications associated with transfusions of G6PD-deficient RBCs because they receive RBCs from donors who are more likely to have G6PD deficiency. This review discusses G6PD deficiency, its importance in transfusion medicine, changes in the RBC antioxidant system (of which G6PD is essential) during refrigerated storage and mechanisms of haemolysis. In addition, as yet unanswered questions that could be addressed by translational and clinical studies are identified and discussed.

Sickle cell trait: is there an increased VTE risk in pregnancy and the postpartum?

Blacks are purported to have a higher venous thromboembolism (VTE) risk than whites. We hypothesized that this might be due, in part, to the greater presence of sickle cell trait (SCT) among blacks. We investigated whether the presence of SCT resulted in a higher VTE incidence in a population predisposed to VTE, the pregnant/postpartum women. Methods: Using a mirrored clinical database that prospectively gathered in- and out-patient information for the years 1998–2008, we collected demographic data, including hemoglobin electrophoreses, on all pregnant/postpartum non-Hispanic women who delivered at a large, diverse, urban hospital. We identified those women who developed VTE either while pregnant or postpartum during those 11 years. Charts initially identified as potential VTE cases were subjected to review to ensure accuracy of VTE coding. Results: Of 12,429 women, 679 non-Hispanic SCT black women, 5,465 non-Hispanic Hemoglobin AA (women with HbA as the only hemoglobin present on electrophoresis, with normal amounts of the minor hemoglobins) black women and 1,162 non-Hispanic HbAA white women were included in the analysis. SCT prevalence was high (11.1%) within this black population as compared to 8.3% in the general non-white population. Proportions with VTE were similar for black SCT and black HbAA groups: 0.44% for the SCT group, 0.49% for non-Hispanic black HbAA women. Black HbAA women had a non-significantly higher proportion of VTE than white HbAA women 0.49% vs 0.26% (RR 1.9, 95%CI:0.6,6.3, p = 0.28). Women with VTE were older than those without VTE (32.2 vs. 27.6 years, p = 0.0002) and the majority of VTE occurred postpartum in all groups, and significantly in the HbAA groups. There was no increase in the incidence of pulmonary emboli in the SCT group. Conclusion: In the largest analysis to date, we could not detect a meaningful difference in peripartum VTE incidence between women with and without sickle cell trait.