Tubular marker excretion in children from families with Balkan nephropathy

Urine biomarkers of kidney injury among adolescents in Nicaragua, a region affected by an epidemic of chronic kidney disease of unknown aetiology

BACKGROUND

An epidemic of chronic kidney disease (CKD) of non-traditional aetiology has been recently recognized by health authorities as a public health priority in Central America. Previous studies have identified strenuous manual work, agricultural activities and residence at low altitude as potential risk factors; however, the aetiology remains unknown. Because individuals are frequently diagnosed with CKD in early adulthood, we measured biomarkers of kidney injury among adolescents in different regions of Nicaragua to assess whether kidney damage might be initiated during childhood.

METHODS

Participants include 200 adolescents aged 12-18 years with no prior work history from four different schools in Nicaragua. The location of the school served as a proxy for environmental exposures and geographic locations were selected to represent a range of factors that have been associated with CKD in adults (e.g. altitude, primary industry and CKD mortality rates). Questionnaires, urine dipsticks and kidney injury biomarkers [interleukin-18, N-acetyl-d-glucosaminidase (NAG), neutrophil gelatinase-associated lipocalin (NGAL) and albumin-creatinine ratio] were assessed. Biomarker concentrations were compared by school using linear regression models.

RESULTS

Protein (3.5%) and glucose (1%) in urine measured by dipstick were rare and did not differ by school. Urine biomarkers of tubular kidney damage, particularly NGAL and NAG, showed higher concentrations in those schools and regions within Nicaragua that were defined a priori as having increased CKD risk. Painful urination was a frequent self-reported symptom.

CONCLUSIONS

Although interpretation of these urine biomarkers is limited because of the lack of population reference values, results suggest the possibility of early kidney damage prior to occupational exposures in these adolescents.

Familial versus environmental factors in Balkan endemic nephropathy in Mehedinti county, Romania, by means of albuminuria and tubular biomarkers: preliminary study

INTRODUCTION AND AIMS

Balkan endemic nephropathy (BEN), a regional tubulointerstitial kidney disease encountered in South-Eastern Europe, with still undefined etiology and inexorable evolution towards end stage renal disease, raises the question of the relative contribution of family and environmental factors in its etiology. In order to evaluate the intervention of these factors, markers of tubular injury have been assessed, this lesion being considered an early renal involvement in BEN.

METHODS

The paper studies relatives of BEN patients currently included in dialysis programmes (for involvement of the family factor) and their neighbors (for involvement of environmental factors) and analyzes them with regard to tubular injury by means of tubular biomarkers (N-acetyl-beta-d-glucosaminidase-NAG and alpha-1-microglobulin), and albuminuria. At the same time, glomerular filtration rate (GFR) (CKD-EPI) was measured. It is considered that, in order to acquire the disease, one should have lived for 20 years in the BEN area. The relatives have been classified according to this criterion.

RESULTS

More evident tubular injury was found in the neighbors of BEN patients living for more than 20 years in the endemic area, which argues in favor of environmental factors. Higher levels of urinary alpha-1-microglobulin and albumin in relatives of BEN patients who had been living for more than 20 years in the area than in relatives with a residence under 20 years, plead for the same hypothesis. GFR was lower in persons who had been living for more than 20 years in the BEN area (neighbors and relatives).

CONCLUSIONS

Environmental factors could be more important in BEN than family factors.

Urinary protein patterns in patients with Balkan endemic nephropathy

PURPOSE

Urinary excretion of beta2-microglobulin (beta2-MG), albumin, immunoglobulin G (IgG) and protein was examined in patients with Balkan endemic nephropathy (BEN), glomerulonephritis (GN) and healthy controls.

METHODS

The proteins were measured in morning urine samples from 74 patients with BEN, 50 healthy persons and 22 patients with GN.

RESULTS

In BEN patients, median values for albumin, beta2-MG and protein were above upper normal limits, but median IgG was inside normal range. All patients with GN had microalbuminuria (MAU) and half of them had increased urinary beta2-MG, which was also found in eleven patients with increased urinary IgG. In BEN patients, there were significant negative correlations between eGFR and all measured urinary proteins, the composition of which changed during the course of BEN. In patients with eGFR > 60 ml/min/1.73 m(2) isolated beta2-MG was the most frequent finding (10/12 patients), but MAU was present in 4/12 patients. In BEN patients with eGFR between 30 and 59 ml/min/1.73 m(2), beta2-MG appeared as often as the combination of beta2-MG and albumin and isolated MAU. Out of 49 BEN patients with eGFR > 30 ml/min/1.73 m(2) 15 had increased urinary IgG either alone (1) or together with beta2-MG (3) or albumin (3) or beta2-MG and albumin (8). In BEN patients with GFR < 30 ml/min/1.73 m(2) only 1/25 had isolated beta2-MG but increased urinary IgG with increased beta2-MG, and albumin was the most frequent.

CONCLUSION

Although low-molecular weight proteinuria was the most frequent urinary finding in BEN patients, MAU was frequently detected in advanced stages of BEN but also in some patients with eGFR > 60 ml/min/1.73 m(2). IgG was increasingly found as eGFR decreased.

Beta2-microglobulin and alpha1-microglobulin as markers of Balkan endemic nephropathy, a worldwide disease

BACKGROUND

 Urine beta2-microglobulin (beta2-MG) was mainly used as a tubular marker of Balkan endemic nephropathy (BEN) but recently alpha1-microglobulin (alpha1-MG) was proposed for the diagnosis of BEN. In this study, the potential of urine beta2-MG, alpha1-MG, albumin, and total protein in the differentiation of BEN from healthy persons and patients with glomerulonephritis (GN) and nephrosclerosis (NS) was examined.

METHODS

 This study involved 47 patients with BEN, 36 with GN, 11 with NS, 30 healthy subjects from BEN families, and 46 healthy subjects from non-BEN families.

RESULTS

 In BEN patients area under the curve (AUC) for urine beta2-MG (0.828) and alpha1-MG (0.782) was higher than for urine albumin (0.740), but in GN patients AUC for urine protein (0.854) and albumin (0.872) was significantly higher than for the two low molecular weight proteins. AUC for all four urinary markers in NS patients was significantly lower than in BEN patients, ranging between 500 and 595. Median urine beta2-MG excretion in BEN patients was 17.5 times higher than in GN patients and 18.3 times higher than in controls; median alpha1-MG excretion was higher only 3.0 and 2.25 times, respectively. In the differentiation of BEN from healthy controls, beta2-MG had higher sensitivity and specificity at the cutoff levels (p < 0.001) than alpha1-MG (p < 0.05). In the differentiation of BEN from GN, beta2-MG was the best marker.

CONCLUSION

 All four urinary markers can be used for the differential diagnosis of BEN, beta2-MG being the best. Like in aristolochic acid nephropathy, beta2-MG seems to be an early marker of tubular damage in BEN.

Time trends in Balkan endemic nephropathy incidence in the most affected region in Serbia, 1977-2009: the disease has not yet disappeared

BACKGROUND

Balkan endemic nephropathy (BEN) is a familial chronic kidney disease, which occurs only in some regions of the Balkan Peninsula. The aim of this study was to determine the main epidemiological features of BEN in the Kolubara region, the most affected region in Serbia, and to try to elucidate the controversial issue of whether or not BEN is tapering off.

METHODS

To evaluate the BEN incidence rates in the municipality of Lazarevac over a 33-year period (1977-2009), we used data of BEN notifications from the BEN Registry located in the Special Hospital for Endemic Nephropathy, Lazarevac. Population data were obtained from the 1981, 1991 and 2002 national censuses by interpolation. BEN incidence rates were standardized according to the European standard population, and their trends were assessed by Poisson regression model and joinpoint analysis.

RESULTS

The age-adjusted BEN incidence rates combined for both sexes over a 33-year period (1977-2009) fitted a significant quadratic (U-shaped) trend (y = 58.44 - 3.76 + 0.10x(2), P = 0.026). Joinpoint analysis showed that the overall age-standardized BEN incidence rates significantly decreased in the first decade of the observed period (1977-89) by an average of 10.0% annually, while a nonsignificant increase of 3.9% per year was recorded in the last two decades (1989-2009).

CONCLUSIONS

Our results revealed that BEN still exists in the Kolubara region. The predicted disappearing scenario of this still mysterious disease has not happened.