Longitudinal Study of Glomerular Hyperfiltration in Adults with Sickle Cell Anemia: A Multicenter Pooled Analysis

Relevance of repeated analyses of albuminuria and glomerular filtration rate in African children with sickle cell anaemia

Glomerular hyperfiltration and albuminuria are frequent kidney abnormalities in children with sickle cell anaemia (SCA). However, little is known about their persistence in African SCA children. This prospective study included 600 steady-state SCA children aged 2-18 years from the Democratic Republic of Congo. Participants were genotyped for apolipoprotein L1 (APOL1) risk variants (RVs) and haem oxygenase-1 (HMOX1) GT-dinucleotide repeats. Kidney abnormalities were defined as albuminuria, hyperfiltration or decreased estimated creatinine-based glomerular filtration rate (eGFRcr). At baseline, 247/600 (41.2%) participants presented with kidney abnormalities: 82/592 (13.8%) with albuminuria, 184/587 (31.3%) with hyperfiltration and 15/587 (2.6%) with decreased eGFRcr. After a median follow-up of 5 months, repeated testing was performed in 180/247 (72.9%) available participants. Persistent hyperfiltration and persistent albuminuria (PA) were present in 29.2% (38/130) and 39.7% (23/58) respectively. eGFR normalized in all participants with a baseline decreased eGFRcr. Haemoglobinuria (p = 0.017) and male gender (p = 0.047) were significantly associated with PA and persistent hyperfiltration respectively. APOL1 RVs (G1G1/G2G2/G1G2) were borderline associated with PA (p = 0.075), while HMOX1 long repeat was not associated with any persistent kidney abnormality. This study reveals that a single screening can overestimate the rate of kidney abnormalities in children with SCA and could lead to overtreatment.

Nontargeted Plasma Proteomic Analysis of Renal Disease and Pulmonary Hypertension in Patients with Sickle Cell Disease

Sickle cell disease (SCD) is characterized by red blood cell sickling, vaso-occlusion, hemolytic anemia, damage to multiple organ systems, and, as a result, shortened life expectancy. Sickle cell disease nephropathy (SCDN) and pulmonary hypertension (pHTN) are common and frequently co-occurring complications of SCD; both are associated with markedly accelerated mortality. To identify candidate circulating biomarkers of SCDN and pHTN, we used mass spectrometry to quantify the relative abundance of >1000 proteins in plasma samples from 189 adults with SCD from the Outcome Modifying Genes in SCD (OMG-SCD) cohort (ProteomeXchange identifier PXD048716). Forty-four proteins were differentially abundant in SCDN, most significantly cystatin-C and collagen α-1(XVIII) chain (COIA1), and 55 proteins were dysregulated in patients with SCDN and pHTN, most significantly insulin-like growth factor-binding protein 6 (IBP6). Network analysis identified a module of 133 coregulated proteins significantly associated with SCDN, that was enriched for extracellular matrix proteins, insulin-like growth factor binding proteins, cell adhesion proteins, EGF-like calcium binding proteins, and several cadherin family members. Collectively, these data provide a comprehensive understanding of plasma protein changes in SCDN and pHTN which validate numerous studies of chronic kidney disease and suggest shared profiles of protein disruption in kidney dysfunction and pHTN among SCD patients.

Urinary angiotensinogen is associated with albuminuria in adults with sickle cell anaemia

We explored the association of novel urinary biomarkers with albumin-creatinine ratio (ACR) in adults with sickle cell anaemia. Of 37 participants, 13 (35.2%) had persistent albuminuria (PA). Urinary levels of clusterin (p = 0.002), retinol-binding protein 4 (p = 0.008), alpha-1 microglobulin (p = 0.002) and angiotensinogen (p = 0.006) were significantly higher in participants with PA than in those without PA. Although univariate analysis showed significant associations between both alpha-1 microglobulin (p = 0.035) and angiotensinogen (p = 0.0021) with ACR, only angiotensinogen was associated with ACR in multivariable analysis (p = 0.04). Our results suggest that urinary angiotensinogen may identify sickle cell anaemia patients at risk for kidney disease.

Glomerular filtration rate abnormalities in sickle cell disease

Sickle cell disease (SCD) is a group of inherited blood disorders affecting the β-globin gene, resulting in the polymerization of hemoglobin and subsequent sickling of the red blood cell. Renal disease, the most common complication in SCD, begins in childhood with glomerular hyperfiltration and then progresses into albuminuria, a fast decline of glomerular filtration, and renal failure in adults. This mini-review focuses on glomerular filtration abnormalities and the mechanisms of hyperfiltration, explores genetic modifiers and methods of estimating glomerular filtration rates, and examines novel biomarkers of glomerular filtration in SCD.