Proteinuria and progression of pediatric chronic kidney disease: lessons from recent clinical studies.

Proteinuria in children with chronic kidney disease (CKD) is common and its etiology differs from that in adults. How proteinuria influences the rate of progression of CKD has been analyzed in multiple retrospective clinical studies and more recently in a few prospective ones. In this review I summarize the results, strengths and weaknesses of each of these studies. The findings of several retrospective studies in children with CKD have confirmed what we have learned from adult studies on the association between proteinuria and worsening kidney function. Larger prospective clinical studies have examined the effects of proteinuria on the rate of decline of kidney function and the risk of end-stage kidney disease. They have also considered children with glomerular and, more importantly, the more common, congenital causes of CKD. Current studies have important strengths but also a few weaknesses that limit the validity of the conclusions which can be drawn. There is still a need for large clinical trials that focus primarily on studying the influence of proteinuria on kidney function and on finding remedies that delay progression.

Uric acid and the kidney.

Uric acid, the end product of purine metabolism, is excreted predominantly by the proximal tubules. Abnormal serum levels of uric acid are due to alterations in production or excretion. Fractional excretion of uric acid is helpful in determining the underlying etiology of hypouricemia or hyperuricemia in children. Abnormalities in the molecular mechanisms that control renal uric acid tubular transport are implicated in various disorders associated with abnormal uric acid levels. Gout is rare in children; yet its presence necessitates evaluation for enzymatic defects in purine metabolism. Well-known effects of uric acid on the kidney include nephrolithiasis and acute kidney injury (AKI) in the setting of tumor lysis. However, recent data suggest that uric acid may be an important factor in the pathogenesis of AKI in general, as well as of chronic kidney disease (CKD) and hypertension. Hence, uric acid may not only be a marker but also a potential therapeutic target in kidney disease. Nonetheless, because of confounders, more studies are needed to clarify the association between uric acid and multifactorial disorders of the kidney.

Expanding the phenotype of proteinuria in Dent disease. A case series.

BACKGROUND: Dent disease is an X-linked recessive renal tubular disorder characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and progressive renal failure (MIM 300009). A recent case series identified four patients with CLCN5 mutations who presented with nephrotic-range proteinuria, histologic evidence of focal segmental and/or global sclerosis, and low molecular weight proteinuria. CASE-DIAGNOSIS/TREATMENT: We characterize the clinical, genetic, and histopathological features of seven unrelated adolescent males with nephrotic-range proteinuria and CLCN5 mutations. Six patients underwent renal biopsy prior to assessing tubular proteinuria. All biopsied patients had either segmental sclerosis (3/6) or segmental increase in mesangial matrix (3/6). Five patients revealed some degree of foot process effacement, but only one patient biopsy revealed >50 % foot process effacement. The attenuated foot process effacement suggests the glomerulosclerosis is not due to a primary podocytopathy. CONCLUSIONS: These data suggest that clinicians should consider a diagnostic evaluation for Dent disease in young males presenting with high-grade proteinuria.

Progression of pediatric CKD of nonglomerular origin in the CKiD cohort.

BACKGROUND AND OBJECTIVES: Congenital anomalies of the kidney and urinary tract and genetic disorders cause most cases of CKD in children. This study evaluated the relationships between baseline proteinuria and BP and longitudinal changes in GFR in children with these nonglomerular causes of CKD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Urine protein-to-creatinine ratio, casual systolic and diastolic BP (normalized for age, sex, and height), and GFR decline were assessed in the prospective CKD in Children cohort study. RESULTS: A total of 522 children, median age 10 years (interquartile range, 7, 14 years) with nonglomerular CKD were followed for a median of 4.4 years. The mean baseline GFR in the cohort was 52 ml/min per 1.73 m(2) (95% confidence interval [95% CI], 50 to 54) and declined 1.3 ml/min per 1.73 m(2) per year on average (95%CI, 1.6 to 1.1). A 2-fold higher baseline urine protein-to-creatinine ratio was associated with an accelerated GFR decline of 0.3 ml/min per 1.73 m(2) per year (95% CI, 0.4 to 0.1). A 1-unit higher baseline systolic BP z-score was associated with an additional GFR decline of 0.4 ml/min per 1.73 m(2) per year (95% CI, 0.7 to 0.1). Among normotensive children, larger GFR declines were associated with larger baseline urine protein-to-creatinine ratios; eGFR declines of 0.8 and 1.8 ml/min per 1.73 m(2) per year were associated with urine protein-to-creatinine ratio <0.5 and ≥0.5 mg/mg, respectively. Among children with elevated BP, average GFR declines were evident but were not larger in children with higher levels of proteinuria. CONCLUSIONS: Baseline proteinuria and systolic BP levels are independently associated with CKD progression in children with nonglomerular CKD.

Sodium modeling attenuates rises in whole-blood viscosity during chronic hemodialysis in children with large inter-dialytic weight gain.

Elevated whole-blood viscosity (WBV) is a risk factor for atherosclerosis and thrombosis. We analyzed WBV during hemodialysis (HD) in children and tested the hypothesis that sodium modeling (NaM) attenuates an increase in WBV. Each of six children underwent two control (C) and two NaM HD sessions, B and E. Rapid decline in sodium (Na) concentration occurred at the beginning of HD in B and at the end in E. We measured WBV at different shear rates (SRs) and documented the amount of fluid removed (FR), change in blood volume (BV), and hematocrit (Hct) before, during, and after HD. The percent increase of WBV in control sessions was significantly different at 2 h and 3 h during and after HD from baseline values. The mean percent change in WBV from baseline increased linearly over time during HD (R2>0.90). Hct, FR, and BV correlated with WBV (P<0.05). The effects of NaM on attenuation of WBV were statistically significant in three subjects with >5% inter-dialytic weight gain (IDWG) (P<0.05). WBV increased during HD in children. NaM appears to attenuate the rise in WBV in children with large IDWG.