Characterization of beta-globin haplotypes using blood spots from a population-based cohort of newborns with homozygous HbS

Investigations of Kidney Dysfunction-Related Gene Variants in Sickle Cell Disease Patients in Cameroon (Sub-Saharan Africa)

Background

Renal dysfunctions are associated with increased morbidity and mortality in sickle cell disease (SCD). Early detection and subsequent management of SCD patients at risk for renal failure and dysfunctions are essential, however, predictors that can identify patients at risk of developing renal dysfunction are not fully understood.

Methods

In this study, we have investigated the association of 31 known kidney dysfunctions-related variants detected in African Americans from multi-ethnic genome wide studies (GWAS) meta-analysis, to kidney-dysfunctions in a group of 413 Cameroonian patients with SCD. Systems level bioinformatics analyses were performed, employing protein-protein interaction networks to further interrogate the putative associations.

Results

Up to 61% of these patients had micro-albuminuria, 2.4% proteinuria, 71% glomerular hyperfiltration, and 5.9% had renal failure. Six variants are significantly associated with the two quantifiable phenotypes of kidney dysfunction (eGFR and crude-albuminuria): A1CF-rs10994860 (P = 0.02020), SYPL2-rs12136063 (P = 0.04208), and APOL1 (G1)-rs73885319 (P = 0.04610) are associated with eGFR; and WNT7A-rs6795744 (P = 0.03730), TMEM60-rs6465825 (P = 0.02340), and APOL1 (G2)-rs71785313 (P = 0.03803) observed to be protective against micro-albuminuria. We identified a protein-protein interaction sub-network containing three of these gene variants: APOL1, SYPL2, and WNT7A, connected to the Nuclear factor NF-kappa-B p105 subunit (NFKB1), revealed to be essential and might indirectly influence extreme phenotypes. Interestingly, clinical variables, including body mass index (BMI), systolic blood pressure, vaso-occlusive crisis (VOC), and haemoglobin (Hb), explain better the kidney phenotypic variations in this SCD population.

Conclusion

This study highlights a strong contribution of haematological indices (Hb level), anthropometric variables (BMI, blood pressure), and clinical events (i.e., vaso-occlusive crisis) to kidney dysfunctions in SCD, rather than known genetic factors. Only 6/31 characterised gene-variants are associated with kidney dysfunction phenotypes in SCD samples from Cameroon. The data reveal and emphasise the urgent need to extend GWAS studies in populations of African ancestries living in Africa, and particularly for kidney dysfunctions in SCD.

Factors Associated With Mechanical Ventilation Use in Children With Sickle Cell Disease and Acute Chest Syndrome

OBJECTIVES

Acute chest syndrome is the leading cause of death in children with sickle cell disease and is generally due to respiratory failure. Epidemiologic factors for a need for mechanical ventilation in children with acute chest syndrome require further clarification.

DESIGN

Retrospective observational study.

SETTING

Nationally representative pediatric inpatient records in the United States by using the Kids' Inpatient Database for the years 2003, 2006, 2009, and 2012.

PATIENTS

Patients age less than 20 years old with a discharge diagnosis of acute chest syndrome.

MEASUREMENTS AND MARIN RESULTS

Data were weighted to estimate annual hospitalizations according to hospital characteristics in the United States. Multivariable logistic regression was conducted to ascertain factors associated with use of mechanical ventilation, after adjusting for patient and hospital characteristics. Total hospitalizations for acute chest syndrome were 5,018 in 2003, 6,058 in 2006, 6,072 in 2009, and 6,360 in 2012. Mechanical ventilation use was associated with comorbidities of obesity (odds ratio, 3.35; 95% CI, 1.94-5.78), obstructive sleep apnea (odds ratio, 3.72; 95% CI, 2.23-6.20), and heart disease (odds ratio, 2.19; 95% CI, 1.47-3.27). In addition, nonblack compared with black children (odds ratio, 1.53; 95% CI, 1.02-2.31) and the fall season (p = 0.018) were associated with mechanical ventilation use.

CONCLUSIONS

Comorbidity of obesity, obstructive sleep apnea, or heart disease could be potentially associated with mechanical ventilation use during an episode of acute chest syndrome. Prospective observational studies would be required to confirm these findings and infer potential interventions for preventing illness severity.

The effects of old and recent migration waves in the distribution of HBB*S globin gene haplotypes

Sickle cell hemoglobin is the result of a mutation at the sixth amino acid position of the beta (β) globin chain. The HBB*S gene is in linkage disequilibrium with five main haplotypes in the β-globin-like gene cluster named according to their ethnic and geographic origins: Bantu (CAR), Benin (BEN), Senegal (SEN), Cameroon (CAM) and Arabian-Indian (ARAB). These haplotypes demonstrated that the sickle cell mutation arose independently at least five times in human history. The distribution of βS haplotypes among Brazilian populations showed a predominance of the CAR haplotype. American populations were clustered in two groups defined by CAR or BEN haplotype frequencies. This scenario is compatible with historical records about the slave trade in the Americas. When all world populations where the sickle cell gene occurs were analyzed, three clusters were disclosed based on CAR, BEN or ARAB haplotype predominance. These patterns may change in the next decades due to recent migrations waves. Since these haplotypes show different clinical characteristics, these recent migrations events raise the necessity to develop optimized public health programs for sickle cell disease screening and management.

Hydroxyurea Use in Young Children With Sickle Cell Anemia in New York State

INTRODUCTION

This study examined hydroxyurea usage in young children with sickle cell anemia within New York State (NYS). The cohort was 273 children with sickle cell anemia born in NYS in 2006-2009 and enrolled essentially continuously in Medicaid for the first 4 years of life.

METHODS

Medicaid data were used to examine hydroxyurea usage in this group by age at first prescription fill, persistence, region, treatment institution, and year. Log-binomial regression models were used to estimate the likelihood of receiving hydroxyurea treatment. Data from birth through 2014 for all members of the study group were assembled and analyzed in 2015.

RESULTS

About 25% of the cohort had at least one filled hydroxyurea prescription by their fifth birthday, and nearly 40% by the end of the study period. The mean proportion of days covered for the first year of therapy was 56.3%. Adherence was also assessed by calculating medication possession ratios for individual treatment periods. Slightly more than one third of treated children showed 80% coverage by these measures. There was a consistent, but not statistically significant, trend toward younger age at first fill. Significant regional and treatment center differences in initiation of hydroxyurea use, but not in persistence after initiation, were noted among NYS centers.

CONCLUSIONS

Subsequent to clinical studies demonstrating safety, current NYS-wide use of hydroxyurea in young children with sickle cell anemia appears to be widespread and increasing. However, practice differences between treatment centers and inadequate adherence may limit the full disease-modifying effects of hydroxyurea.

Beta-globin gene haplotypes among cameroonians and review of the global distribution: is there a case for a single sickle mutation origin in Africa?

Studies of hemoglobin S haplotypes in African subpopulations have potential implications for patient care and our understanding of genetic factors that have shaped the prevalence of sickle cell disease (SCD). We evaluated HBB gene cluster haplotypes in SCD patients from Cameroon, and reviewed the literature for a global distribution. We reviewed medical records to obtain pertinent socio-demographic and clinical features for 610 Cameroonian SCD patients, including hemoglobin electrophoresis and full blood counts. RFLP-PCR was used to determine the HBB gene haplotype on 1082 chromosomes. A systematic review of the current literature was undertaken to catalogue HBB haplotype frequencies in SCD populations around the world. Benin (74%; n = 799) and Cameroon (19%; n = 207) were the most prevalent haplotypes observed among Cameroonian patients. There was no significant association between HBB haplotypes and clinical life events, anthropometric measures, hematological parameters, or fetal hemoglobin (HbF) levels. The literature review of the global haplotype distributions was consistent with known historical migrations of the people of Africa. Previously reported data from Sudan showed a distinctly unusual pattern; all four classical haplotypes were reported, with an exceptionally high proportion of the Senegal, Cameroon, and atypical haplotypes. We did not observe any significant associations between HBB haplotype and SCD disease course in this cohort. Taken together, the data from Cameroon and from the wider literature suggest that a careful reassessment of African HBB haplotypes may shed further light on the evolutionary dynamics of the sickle allele, which could suggest a single origin of the sickle mutation.

Sickle cell in Latin America and the United States [corrected]

Latin Americans are an underappreciated population affected by sickle cell disease (SCD). Sickle trait and SCD exist throughout Latin America and U.S. Latino communities. We describe the epidemiology and genetic heterogeneity of SCD among Latin Americans, and fetal hemoglobin expression. National population-based newborn screening for SCD is limited to Brazil, Costa Rica, and the U.S. Available and extrapolated data suggest that over 6,000 annual births and 100,000-150,000 Latin Americans are affected by SCD. This comprehensive review highlights the substantial numbers and population distribution of SCD and sickle trait in Latin America, and where national newborn screening programs for SCD exist.

An evolutionary perspective of how infection drives human genome diversity: the case of malaria

Infection with malaria parasites has imposed a strong selective pressure on the human genome, promoting the convergent evolution of a diverse range of genetic adaptations, many of which are harboured by the red blood cell, which hosts the pathogenic stage of the Plasmodium life cycle. Recent genome-wide and multi-centre association studies of severe malaria have consistently identified ATP2B4, encoding the major Ca(2+) pump of erythrocytes, as a novel resistance locus. Evidence is also accumulating that interaction occurs among resistance loci, the most recent example being negative epistasis among alpha-thalassemia and haptoglobin type 2. Finally, studies on the effect of haemoglobin S and C on parasite transmission to mosquitoes have suggested that protective variants could increase in frequency enhancing parasite fitness.

Fetal hemoglobin levels in African American and Hispanic children with sickle cell disease at baseline and in response to hydroxyurea

The degree of fetal hemoglobin (HbF) expression is a major determinant of phenotypic severity of sickle cell disease (SCD). Genetic regulation of HbF production is complex and can vary among ethnic groups. The pediatric sickle cell population at our institution is approximately half Hispanic, nearly all from the Dominican Republic. Hydroxyurea (HU) is the only Food and Drug Administration (FDA)-approved drug to ameliorate symptoms of SCD. We retrospectively compared baseline and HU-induced percent HbF (%HbF) in African American (AA) and Hispanic (H) patients aged 4 to 21 years with homozygous Sickle hemoglobin or HbSβ(0)Thalassemia. No significant differences were detected in average baseline %HbF between AA (N=48) and H (N=58) patients (P=0.63). In the subset of children taking HU who reached maximum tolerated dose (MTD), no differences were found between the ethnic groups in laboratory response to drug, measured by %HbF at MTD (P=0.28), the increase in %HbF (P=0.31) or mean red cell volume (MCV) (P=0.93), or the MTD of HU (P=0.95). Regulation of HbF at baseline and in response to HU are comparable between Hispanics and African Americans at our center. If generalizable, our results support combining these 2 groups in future clinical and translational analyses focused on HbF and response to HU in this ethnically mixed patient population.

Ethical implications and practical considerations of ethnically targeted screening for genetic disorders: the case of hemoglobinopathy screening

The prevalence of hemoglobinopathies differs among populations due to genetic differences and due to the protective effects of the heterozygote (carrier) state against malaria. Because of the difference in genetic distribution, public health programs have weighed the ethical versus practical implications of ethnically targeted versus universal newborn, and where applicable, prenatal screening. We examine newborn and prenatal screening for hemoglobinopathies in relation to the use of 'race' and ethnicity to assess risk for genetic conditions. First, categories of race/ethnicity are social constructs, therefore, observed or self-identified broad racial/ethnic categories are correlated but not necessarily reliable indicators of geographic ancestry or genetic risk. Second, targeting based on ethnicity poses serious issues of logistics and equity for public health programs and clinical services. In the past, newborn screening for hemoglobinopathies in the United States and United Kingdom was often selective, targeted to women of certain ethnic groups or areas with large concentrations of ethnic minority groups. Presently, newborn screening for hemoglobinopathies is universal in both countries and programs emphasize that individuals of all ethnic backgrounds are at risk for carrying a hemoglobin genetic variant. Reported race/ethnicity is still used as a criterion for offering prenatal carrier testing in the United States, where it is not a public health responsibility. In the United Kingdom, prenatal screening under the National Health Service is universal in high-prevalence areas and in low-prevalence areas is targeted based on reported ancestry. The continued use of targeted prenatal screening in both countries reflects the different purposes and modes of laboratory testing in newborn and prenatal screening. The ethical imperative to identify as many affected infants with life-threatening conditions as possible in newborn screening programs is not applicable to prenatal carrier testing. Because newborn screening dried blood spot specimens are tested for multiple disorders, targeted screening poses serious logistical challenges which is not the case in prenatal screening.

Sickle cell disease: current activities, public health implications, and future directions

Sickle cell disease (SCD) is a genetic blood disorder caused by abnormal hemoglobin that damages and deforms red blood cells (RBCs). The abnormal red cells break down, causing anemia, and obstruct blood vessels, leading to recurrent episodes of severe pain and multiorgan ischemic damage. SCD affects millions of people throughout the world and is particularly common among people whose ancestors come from sub-Saharan Africa. Sickle cell trait (SCT) is an inherited condition in which both normal hemoglobin and sickle hemoglobin are produced in the RBCs. SCT is not a type of sickle cell disease. People with SCT are generally healthy. In SCD, clinical severity varies, ranging from mild and sometimes asymptomatic states to severe symptoms requiring hospitalization. Symptomatic treatments exist, but there is no cure for SCD. Although there has been extensive clinical and basic science research in SCD, many public health issues, such as blood safety surveillance, compliance with immunizations, follow-up of newborns with positive screening tests, stroke prevention, pregnancy complications, pain prevention, quality of life, and thrombosis, in people with SCT remain unaddressed. Currently, efforts are under way to strengthen SCD-related activities within the Centers for Disease Control and Prevention (CDC). To date, several activities are being or have been conducted by centers within CDC, including quality assurance of newborn screening tests for SCD, morbidity and mortality studies, genetic studies, and studies focusing on the protective effects of SCT for malaria. This paper discusses the public health implications of SCD, summarizes SCD-related activities within CDC, and points to future directions that the agency can take to begin to address some of these issues.

Storage and use of residual dried blood spots from state newborn screening programs

OBJECTIVES

To provide current data for policy discussions and to assess future needs among newborn screening programs regarding the storage and use of residual dried blood spots (DBS) in the United States.

STUDY DESIGN

An electronic questionnaire was administered to U.S. state health department laboratory directors in 2003.

RESULTS

Responses were received from 49 of the 50 states. Approximately half of them stored residual DBS for more than 6 months, 57% did not have a written policy that determines how residual DBS can or cannot be used, and 16% informed parents that DBS might be retained. Residual DBS were used by 74% of respondents for evaluation of newborn screening tests, by 52% for clinical or forensic testing, and by 28% for epidemiologic studies. Use of DBS was reported more frequently by states with extended storage. When asked if they might participate in an anonymous multistate epidemiologic study by contributing unlinked DBS, 41% responded affirmatively.

CONCLUSIONS

More states have used residual DBS for evaluating newborn screening tests than for epidemiologic studies. There is potential interest among states in using unlinked DBS for multistate studies and a need for written policies addressing all uses of residual DBS.

The cost effectiveness of universal versus selective newborn screening for sickle cell disease in the US and the UK: a critique

We reviewed several cost-effectiveness analyses that modelled the costs and yield of newborn screening for sickle cell disease (SCD) in the US and the UK and discuss the ways in which newborn screening policies in each country evolved with regard to the results of the analyses. Each of the reviewed studies compared the projected cost of universal screening with that of selective screening of children from specific ethnic groups. Despite variability in assumptions, the studies concurred that universal screening in areas with low SCD prevalence would result in a higher cost per case detected, compared with selective screening of children in high-risk ethnic groups. Investigators expressed differing opinions about the economic justification of universal screening, which reflected differences in the understanding of cost effectiveness and in how study questions were framed. Ultimately, policy makers in both countries decided in favour of universal screening, which appears to reflect a growing consensus that ethnically targeted newborn screening is not an acceptable public health strategy. One way to interpret this outcome is that considerations of equity and logistics, including potential stigmatisation, missed cases, and the perceived difficulty and discomfort in ascertaining ethnicity or in separating specimens, trumped economic calculations regarding the relative efficiency of targeted screening. It is not the case that policy makers explicitly favoured equity over economic optimisation; rather, they appear to have given more credence and value to the expert opinion of screening specialists than to the results of economic analyses.