Clinical and genetic predictors of renal dysfunctions in sickle cell anaemia in Cameroon

Abstract

Micro-albuminuria and glomerular hyperfiltration are primary indicators of renal dysfunctions in Sickle Cell Disease (SCD), with more severe manifestations previously associated with variants in APOL1 and HMOX1 among African Americans. We have investigated 413 SCD patients from Cameroon. Anthropometric variables, haematological indices, crude albuminuria, albumin-to-creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) were measured. Patients were genotyped for 3·7 kb alpha-globin gene (HBA1/HBA2) deletion, and for variants in APOL1 (G1/G2; rs60910145, rs73885319, rs71785313) and HMOX1 (rs3074372, rs743811). The median age was 15 years; the majority presented with micro-albuminuria (60·9%; n = 248), and approximately half with glomerular hyperfiltration (49·5%; n = 200). Age, male sex, haemoglobin level, leucocyte count, mean corpuscular volume, blood pressure, body mass index and creatinine levels significantly affected albuminuria and/or eGFR. Co-inheritance of alpha-thalassaemia was protective against macro-albuminuria (P = 0·03). APOL1 G1/G2 risk variants were significantly associated with the ACR (P = 0·01) and borderline with eGFR (P = 0·07). HMOX1 - rs743811 was borderline associated with micro-albuminuria (P = 0·07) and macro-albuminuria (P = 0·06). The results revealed a high proportion of micro-albuminuria and glomerular hyperfiltration among Cameroonian SCD patients, and support the possible use of targeted genetic biomarkers for risks assessment.

Keywords: APOL1; HMOX1; albuminuria; glomerular filtration rate; sickle cell disease.

Figure 1. Clinical Factors affecting eGFR values in SCD: Age, gender, BMI and blood pressure

A. Scatter plots illustrating the relationship between eGFR values and age in the SCD patient cohort, using CKD-EPI (r = −0.550, p < 0.0001. Similar results were found for Cockcroft-Gault (r = −0.168, p < 0.0001) and Modification of Diet in Renal Disease (MDRD; r = −0.523, p < 0.0001) equations. The red line indicates a line of best fit, fitted to the data. B. Box and whisker plots showing the association of eGFR values with gender. Box and whisker plots illustrating the distribution of eGFR values conditioned on gender. The eGFR values were calculated using CKD-EPI. Significant results are indicated using * (p < 0.05); similar significant results were obtained using MDRD equations and Cockcroft-Gault equations. The horizontal lines that constitute the ‘box’ correspond to the lower quartile, median and upper quartile parameters. The length of the ‘whiskers’ that extend from the box in the upwards and downwards direction represent a value of 1.5 times the interquartile range. Values that lie outside this are considered outliers, or extreme values. C. Scatter plots illustrating the relationship between eGFR values and BMI Calculated using the CKD-EPI (r = 0.529, p < 0.0001) equation. Similar results were found using MDRD (r = −0.520, p < 0.0001) and Cockcroft-Gault (r = −0.164, p = 0.018) equations. The BMI (kg/m²) variable is displayed on the x-axis, with the eGFR values on the y-axis. The red line indicates a line of best fit, fitted to the data. D. Scatter plots illustrating the relationship between eGFR values and logSBP calculated using the CKD-EPI (r = −0.367, p < 0.0001) equations. Similar results were found with MDRD (r = − 0.407, p < 0.0001) and Cockcroft-Gault (p = 0.018) equations. The log(SBP) variable is displayed on the x-axis, with the eGFR values on the y-axis. The red line indicates a line of best fit, fitted to the data. Similar significant relationship between eGFR values and log(diastolic blood pressure) was also found, calculated using CKD-EPI (r = −0.296, p < 0.0001), the MDRD (r = −0.300, p < 0.0001) and Cockcroft-Gault (r = −0.164, p = 0.001) equations. BMI: body mass index; CKD-EPI: Chronic Kidney Disease Epidemiology Collaboration equation; eGFR: estimated glomerular filtration rate; F: female; M: male; SBP: systolic blood pressure; SCD: sickle cell disease.

Figure 2. Clinical Factors associated with Albuminuria in SCD: Age, and haematological indices

Scatter plot illustrating the positive relationship between age (y-axes) and log crude albuminuria, (r = 0.142, p = 0.004) (A), log Leucocyte count (r = 0.116, p = 0.0202) (B); MCV (r = 0.167, p = 0.008) (C) and a nearly significant negative nature of the relationship with Hb level (r = −0.091, p = 0.069) (D). The red lines indicate a line of best fit, fitted to the data. Hb: haemoglobin; MCV: mean corpuscular volume.

Figure 3. Box and whisker plots showing the association of APOL1 G1/G2 with crude albuminuria, ACR, and eGFR values in the SCD patient cohort

Box and whisker plots illustrating the distribution of (Panel A) crude albuminuria, (Panel B) ACR and (Panel C) eGFR (calculated using the CKD-EPI equation) values conditioned on the APOL1 G1/G2 polymorphism, based on the presence of zero (n = 333), one (n = 40) or two (n = 5) minor alleles. The horizontal lines that constitute the ‘box’ correspond to the lower quartile, median and upper quartile parameters. The length of the ‘whiskers’ that extend from the box in the upwards and downwards direction represent a distance to the maximum and minimum values, respectively. Significant results are indicated using * (p < 0.05). ACR: albumin/creatinine ratio; CKD-EPI: Chronic Kidney Disease Epidemiology Collaboration equation; eGFR: estimated glomerular filtration rate; SCD: sickle cell disease.