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Background: People with sickle cell disease (SCD) have an elevated estimated glomerular filtration rate (eGFR) compared to the general population and this may alter the usual creatinine-based eGFR cutoffs for which physiologic evidence of kidney dysfunction is apparent. This study aimed to identify eGFR thresholds for hyperkalemia and metabolic acidosis in patients with SCD Methods: This was a cross-sectional analysis of 733 patients with severe (hemoglobin SS or Sβ0-thalassemia) SCD genotype, 238 patients with moderate (hemoglobin SC or Sβ+-thalassemia) SCD genotype, and 1,333 age- and sex-matched African Americans from the National Health and Nutrition Examination Survey (NHANES). The prevalence of hyperkalemia and metabolic acidosis were compared by eGFR category. Cutoffs for hyperkalemia and metabolic acidosis were determined using generalized additive models. Results: Hyperkalemia and metabolic acidosis were more common in those with severe SCD genotype (13% and 21%, respectively) compared to in NHANES (0.3% and 5%, respectively); the prevalence rates in the moderate SCD genotype were intermediate for hyperkalemia (3%) and metabolic acidosis (11%). The proportion of patients with hyperkalemia and metabolic acidosis progressively increased with lower eGFR category in both SCD genotype groups. The eGFR thresholds for hyperkalemia and metabolic acidosis were higher in the severe (85 and 91 mL/min/1.73m2, respectively) and moderate (52 and 102 mL/min/1.73m2, respectively) SCD genotypes compared with NHANES (34 and 46 mL/min/1.73m2). Conclusions: We demonstrate that hyperkalemia and metabolic acidosis are more common and occur at higher eGFR values in patients with SCD compared to age- and sex-matched African Americans, including in eGFR ranges considered to be normal. Future studies using redefined creatinine-based eGFR thresholds for abnormal kidney function may identify high-risk patients for earlier intervention strategies and referral for specialized renal care in SCD.

Von Hippel–Lindau protein (VHL) is essential to hypoxic regulation of cellular processes. VHL promotes proteolytic clearance of hypoxia‐inducible transcription factors (HIFs) that have been modified by oxygen‐dependent HIF‐prolyl hydroxylases. A homozygous loss‐of‐function VHLR200W mutation causes Chuvash erythrocytosis, a congenital disorder caused by augmented hypoxia‐sensing. Homozygous VHLR200W results in accumulation of HIFs that increase transcription of the erythropoietin gene and raise hematocrit. Phlebotomies reduce hematocrit and hyperviscosity symptoms. However, the major cause of morbidity and mortality in Chuvash erythrocytosis is thrombosis. Phlebotomies cause iron deficiency, which may further elevate HIF activity and transferrin, the HIF‐regulated plasma iron transporter recently implicated in thrombogenesis. We hypothesized that transferrin is elevated in Chuvash erythrocytosis, and that iron deficiency contributes to its elevation and to thrombosis. We studied 155 patients and 154 matched controls at steady state and followed them for development of thrombosis. Baseline transferrin was elevated, and ferritin reduced in patients. VHLR200W homozygosity and lower ferritin correlated with higher erythropoietin and transferrin. During 11 years of follow‐up, risk of thrombosis increased 8.9‐fold in patients versus controls. Erythropoietin elevation, but not hematocrit or ferritin, correlated with thrombosis risk. Unexpectedly, transferrin elevation associated with reduced rather than increased thrombosis risk. The A allele of the promoter EPO single nucleotide polymorphisms (SNP), rs1617640, associated with elevated erythropoietin and increased thrombosis risk, whereas the A allele of the intronic TF SNP, rs3811647, associated with higher transferrin and protection from thrombosis in patients. Our findings suggest an unexpected causal relationship between increased transferrin and protection from thrombosis in Chuvash erythrocytosis.

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Summary Ischaemic stroke is a common complication of sickle cell disease (SCD) and without intervention can affect 11% of children with SCD before the age of 20. Within the Trans‐Omics for Precision Medicine (TOPMed), a genome‐wide association study (GWAS) of ischaemic stroke was performed on 1333 individuals with SCD from Brazil (178 cases, 1155 controls). Via a novel Cox proportional‐hazards analysis, we searched for variants associated with ischaemic stroke occurring at younger ages. Variants at genome‐wide significance (p < 5 × 10−8) include two near genes previously linked to non‐SCD early‐onset stroke (<65 years): ADAMTS2 (rs147625068, p = 3.70 × 10−9) and CDK18 (rs12144136, p = 2.38 × 10−9). Meta‐analysis, which included the independent SCD cohorts Walk‐PHaSST and PUSH, exhibited consistent association for variants rs1209987 near gene TBC1D32 (p = 3.36 × 10−10), rs188599171 near CUX1 (p = 5.89 × 10−11), rs77900855 near BTG1 (p = 4.66 × 10−8), and rs141674494 near VPS13C (1.68 × 10−9). Findings from this study support a multivariant model of early ischaemic stroke risk and possibly a shared genetic architecture between SCD individuals and non‐SCD individuals younger than 65 years.