Enos rs1799983 polymorphism is associated with persistent albuminuria in children and adolescents with sickle cell anemia

Aim: Albuminuria is associated with morbidity and early mortality in individuals with Sickle Cell Anemia (SCA). However, albuminuria is often intermittent in children with SCA. Children at the highest risk of Chronic Kidney Disease (CKD) cannot be identified prior to the appearance of irreversible albuminuria and the physiopathology is not well understood. Endothelial Nitric Oxide Synthase gene (eNOS) polymorphisms have been associated with the synthesis of variable quantities of Nitric Oxide (NO) and may influence the risk of sickle cell nephropathy. This study aimed to evaluate the association between persistent albuminuria and the rs1799983 and rs2070744 polymorphisms in a population of children and adolescents with SCA from Minas Gerais, Brazil. Methods: We recruited steady-state participants at Fundação Hemominas outpatient clinic with SCA. Random-spot urine specimens were collected during routine visits. Albuminuria was defined as urine albumin/creatinine ratio > 30 mg/g. Participants were prospectively categorized by the presence or absence of albuminuria at baseline and at the follow-up urine test. Those with albuminuria at baseline and at the follow-up urine test were considered to have persistent albuminuria. Steady-state laboratory data were obtained from medical records. Genotyping of rs1799983 and rs2070744 polymorphisms was performed by qPCR. Results: The 355 participants evaluated in this study were between 1.6 and 20.2 years of age at the baseline (10.5 ± 4.6) and 186 (52.4%) were males. The mean follow-up period was 2.5 years (SD = 1.2; range 6m–6.2y), providing 874 patient-years. At the baseline, 263 (74.1%) participants were receiving intensification therapy (hydroxyurea, chronic blood transfusion, or both). Fifth-three (14.9%) presented persistent albuminuria. The odds of persistent albuminuria was higher in children and adolescents who had the GT or TT genotype (n = 28/136; 20.6%) of the rs1799983 polymorphism when compared to those with the GG genotype (n = 25/219; 11.4%) (OR = 2.0, 95% CI 1.1–3.6; p = 0.022). The cumulative incidence of persistent albuminuria for the GG group was 23.8% (SE = 6.0%), while that for the GT or TT group was 35.8% (SE = 7.1%; p = 0.025). The indirect bilirubin and reticulocytes levels of participants who had the GT or TT genotype were significantly higher when compared to those with the GG genotype (2.6 ± 1.7 mg/dL and 1.7 ± 1.1 mg/dL, respectively; p < 0.001; 15.6 ± 4.1% and 13.6 ± 4.6%, respectively; p = 0.002). Additionally, the hemoglobin level of children and adolescents who had the GT or TT genotype was significantly lower when compared to those with the GG genotype (7.6±0.8 g/dL and 8.1±1.1%, respectively; p = 0.007). There was no association between persistent albuminuria and rs2070744 polymorphism genotypes. Discussion: NO has vasodilator effect vital for maintenance of vascular function. The rs1799983 has been associated with reduced NO production. Our study provides data to understand the physiopathology of albuminuria in children and adolescents with SCA and sheds light on a potential genetic marker for CKD development. Additionally, the association of rs1799983 genotypes with hemolysis markers suggests that this polymorphism can influence other clinical manifestations of SCA. Conclusion: We found that eNOS rs1799983 polymorphism was associated with an increased risk of persistent albuminuria in individuals with SCA.