Procoagulant activity in patients with sickle cell trait

Early-onset indicators of a hypercoagulable state and clinical complications in a cohort of children with sickle cell trait

Adults with sickle cell trait (SCT) have a procoagulant state with increased risk of thromboembolism, but limited data are available for children. We compared the coagulation profile of children with SCT, different sickle cell disease (SCD) genotypes, and healthy controls. Compared to controls and similarly to HbSC patients, 41 SCT children (mean age 6.85 years; 20 males; 88% Africans) had a characteristic procoagulant profile: higher levels of factor VIII, von Willebrand factor (VWF) Ag and CBA, D-dimer; lower levels of ADAMTS 13 activity, ADAMTS13 activity: VWFAg, plasminogen activator inhibitor, tissue plasminogen activator. Moreover, 13/41 had clinical complications of SCD, five requiring hospitalization.

D-Dimer in African Americans: Whole Genome Sequence Analysis and Relationship to Cardiovascular Disease Risk in the Jackson Heart Study

OBJECTIVE

Plasma levels of the fibrinogen degradation product D-dimer are higher among African Americans (AAs) compared with those of European ancestry and higher among women compared with men. Among AAs, little is known of the genetic architecture of D-dimer or the relationship of D-dimer to incident cardiovascular disease.

APPROACH AND RESULTS

We measured baseline D-dimer in 4163 AAs aged 21 to 93 years from the prospective JHS (Jackson Heart Study) cohort and assessed association with incident cardiovascular disease events. In participants with whole genome sequencing data (n=2980), we evaluated common and rare genetic variants for association with D-dimer. Each standard deviation higher baseline D-dimer was associated with a 20% to 30% increased hazard for incident coronary heart disease, stroke, and all-cause mortality. Genetic variation near F3 was associated with higher D-dimer (rs2022030, β=0.284, P=3.24×10^-11). The rs2022030 effect size was nearly 3× larger among women (β=0.373, P=9.06×10^-13) than among men (β=0.135, P=0.06; P interaction =0.009). The sex by rs2022030 interaction was replicated in an independent sample of 10 808 multiethnic men and women (P interaction =0.001). Finally, the African ancestral sickle cell variant (HBB rs334) was significantly associated with higher D-dimer in JHS (β=0.507, P=1.41×10^-14), and this association was successfully replicated in 1933 AAs (P=2.3×10^-5).

CONCLUSIONS

These results highlight D-dimer as an important predictor of cardiovascular disease risk in AAs and suggest that sex-specific and African ancestral genetic effects of the F3 and HBB loci contribute to the higher levels of D-dimer among women and AAs.

Bilateral Pulmonary Embolism after a Short-Haul Flight in a Man with Multiple Risk Factors including Sickle Cell Trait

We report a case of pulmonary embolism (PE) in an Afro-Caribbean man following a short commercial flight of less than 5,000 kilometers (Km) in economy class with a 1-month interval between journeys. He had an elevated body mass index (BMI) and sickle cell trait (SCT) with hyperhomocysteinemia. No other preexisting source of venous thrombosis was found. We posit that venous thromboembolism (VTE) and/or PE may have been a complication of SCT in an individual with other multiple risk factors. We discuss the possible interaction of these risk factors for VTE and/or PE and the implications for travelers at risk. The need for a PE risk score and guidelines for the prophylaxis of thromboembolism among travelers exists.

Individual variability in response to a single sickling event for normal, sickle cell, and sickle trait erythrocytes

Hemoglobin S (Hb-S) polymerization is the primary event in sickle cell disease causing irreversible damage to red blood cell (RBC) membranes over repeated polymerization cycles. A single polymerization triggered by a hypoxic environment was reported to result in reversibly (upon reoxygenation) decreased RBC deformability and increased mechanical fragility (MF). Individualized responses have not been reported, although RBC fragility can vary significantly even among healthy individuals. This study evaluates individual variability in response to a single hypoxia-induced sickling event, through changes in RBC MF. Blood was drawn from 10 normal (AA), 11 sickle cell (SS), and 7 sickle trait (AS) subjects-with Hb-S fraction, osmotic fragility, and medical history also collected. Mechanical stress was applied using a bead mill at 50-Hz oscillation for 0.5-30 minutes. MF profiles here give percent hemolysis upon successive durations of stressing. MF was measured for AA, SS, and AS cells-each equilibrated (1) with air, (2) with nitrogen in an anaerobic chamber, and (3) with air after the hypoxic event. While AA subjects exhibited significantly different changes in fragility upon hypoxia, in all cases there was recovery to close to the initial MF values on reoxygenation. For AS subjects, recovery at reoxygenation was observed only in about half of the cases. Fragility of SS cells increased in hypoxia and decreased with reoxygenation, with significantly variable magnitude of recovery. The variability of response for individual AS and SS subjects indicates that some are potentially at higher risk of irreversible hypoxia-induced membrane damage.

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.