Differentiation of proteinurias with electrophoresis

Low Molecular Weight Proteinuria in Children with Distal Renal Tubular Acidosis

Distal renal tubular acidosis (dRTA) (MIM #267300, #602722 and #179800) is a rare inherited tubulopathy characterized by the inability of the distal tubule to acidify the urine with consecutive systemic acidosis. The clinical features include polyuria, polydipsia, poor appetite, failure to thrive, short stature and rickets. Prominent biochemical features are hypokalemia, hypercalciuria and hypocitraturia. There are reports on patients who presented with unusual biochemical features such as low molecular proteinuria, hypophosphatemia, hypouricemia, generalized hyperaminioaciduria, hyperoxaluria and other making diagnostic confusion to the clinicians. In this work, we report on a series of 8 children with clinically, biochemically and genetically proven dRTA who present with low molecular proteinuria at the disease onset. With metabolic compensation of the disease, there was complete resolution of the low molecular weight protenuria and other proximal tubular abnormalities in all children. Late recognition of the disease with long standing hypokalemia and acidosis may result in abnormal expression and function of the transporters in the proximal tubules. Sodium dodecyl sulphate polyacrylamide gel electrophoeresis is an accurate method for detection and follow up of patients with low molecular weight proteinuria.

The Spectrum of Kidney Diseases in Children Associated with Low Molecular Weight Proteinuria

BACKGROUND

Proteinuria, in addition to haematuria, is the most important laboratory parameter in patients with nephro-urological diseases. Low molecular weight proteinuria (LMWP) is of particular importance because some diseases genetic and tubulointerstitial are diagnosed based on its presence.

AIM

The purpose of this study is to describe the clinical features, the course and outcome of pediatric patients with a renal disease associated with LMWP.

MATERIAL AND METHODS

This retrospective observational study included 250 pediatric patients with various kidney diseases in which the type of proteinuria was defined by 4-20% gradient gel sodium dodecyl sulphate polyacrylamide gel (SDS-PAG) electrophoresis.

RESULTS

Isolated LMWP was detected in 12% of patients, while mixed glomerulotubular proteinuria was detected in 18% of patients. It was detected in all patients with the Dent-1/2 disease, Lowe's syndrome and secondary Fanconi syndrome. Transient LMWP was also detected in a series of 12 patients with distal renal tubular acidosis. In patients with nephrotic syndrome, it was associated with corticoresistence and unfavourable clinical course.

CONCLUSION

This study contributes to the understanding of the clinical spectrum of various kidney diseases associated with LMWP, their natural course, and the effect of therapy.

High-resolution gel electrophoresis and sodium dodecyl sulphate–agarose gel electrophoresis on urine samples for qualitative analysis of proteinuria in dogs

The aims of the current study were to assess whether sodium dodecyl sulphate–agarose gel electrophoresis (SDS-AGE) and high-resolution electrophoresis (HRE) can identify dogs with a urinary protein-to-creatinine ratio (UPC ratio) >0.2 and whether HRE can provide preliminary information about the type of proteinuria, using SDS-AGE as a reference method. HRE and SDS-AGE were conducted on 87 urine samples classified according to the International Renal Interest Society as non-proteinuric (NP; UPC ratio: <0.20; 32/87), borderline proteinuric (BP; UPC ratio: 0.21–0.50; 15/87), or proteinuric (P; UPC ratio: >0.51; 40/87). SDS-AGE and HRE were positive in 14 out of 32 and 3 out of 32 NP samples and in 52 out of 55 and 40 out of 55 samples with a UPC ratio >0.20, respectively. The concordance between HRE or SDS and UPC ratio was comparable (κ = 0.59; κ = 0.55). However, specificity (90%) and positive likelihood ratio (7.76) were higher for HRE than for SDS-AGE (56% and 2.16) while sensitivity was lower (73% vs. 94%). The analysis of HRE results revealed that a percentage of albumin >41.4% and an albumin/α1-globulin ratio (alb/α1 ratio) >1.46 can identify samples classified by SDS-AGE as affected by glomerular proteinuria while a percentage of α1-globulin >40.8% and an alb/α1 ratio <0.84 can identify samples classified by SDS-AGE as affected by tubular proteinuria. In conclusion, both SDS-AGE and HRE could misclassify samples with a UPC ratio higher or lower than 0.20. Therefore, UPC ratio must always be determined before conducting these tests. The percentage of albumin and α1-globulin or the alb/α1 ratio determined by HRE can provide preliminary information about the origin of proteinuria.

Characterization of proteinuria in asymptomatic family members and household contacts of children with hepatitis B virus-associated membranous nephropathy

The biosocial background in which the hepatitis B virus (HBV) carrier state with membranous nephropathy (MN) develops was studied by evaluating HBV carriage and proteinuria among 195 family members and household contacts of 31 index HBV carrier children with MN. Unrelated individuals from the communities of these index cases who were negative for HBV served as controls (n = 123). HBV was determined by using third-generation enzyme-linked immunosorbent assay, slot-blot hybridization, and nested polymerase chain reaction. Patterns of proteinuria were determined by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis; immunoglobulin G and haptoglobulin were suggestive of MN. Seventy-two members (36.9%) of the study group (n = 195) were HBV carriers; 21 of these carriers (29.2%) had proteinuria. Twenty-eight members (41.2%) of the study group who were HBV negative (n = 68) and 26.8% of the controls showed proteinuria. This lack of association between HBV carriage and proteinuria remained when controlled for sex and family relationship. HBV was not protective against the development of proteinuria. Proteinuria suggestive of MN was strongly associated with an abnormal protein-creatinine ratio (P: = 0.001), but was not significantly different between subjects and controls (8.7% versus 6.5%; P: = 0.5). Genetic influences or environmental exposures in these subjects may be responsible for the proteinuria, suggesting underlying glomerular basement membrane damage. Discordance between the HBV carrier state and patterns of proteinuria in the study group suggest that HBV and MN may not be causally related or may reflect exceptional interaction between specifically vulnerable individuals and HBV.

Oedema in childhood

Oedema is a common childhood problem with important public health implications. It is an abnormal accumulation of fluid in the interstitial space which might result from a decrease in intravascular oncotic pressure, an increase in intravascular hydrostatic pressure, an increase in capillary permeability or impaired lymphatic drainage. Renal sodium retention is an important factor in generalised oedema. This article reviews the pathophysiology and aetiology of oedema in children and suggests an approach to evaluation, diagnosis and management of the problem.

Clinical analysis of human urinary proteins using high resolution electrophoretic methods

The application of isoelectric focusing (IEF), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) for high resolution electrophoretic analysis of human urinary proteins is reviewed. In each case, the information is tabulated chronologically with details of sample preparation, electrophoretic system, detection method and clinical application. The text includes an historical perspective of the use of each method for urinalysis and a detailed review of the application of the methods to the investigation of renal disease, renal transplantation, Bence Jones proteinuria (BJP), diabetes mellitus, cadmium toxicity, nephrolithiasis and cancers of the urogenital tract.

Sodium dodecyl sulphate polyacrylamide gel electrophoresis of urinary proteins in steroid-responsive and steroid-resistant nephrotic syndrome in children

Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE) of urinary proteins was performed in 56 children with nephrotic syndrome during relapse, of whom 31 had their urines tested within 2 months of the onset of disease. The urines of all 32 steroid-sensitive [presumed minimal change nephrotic syndrome (MCNS)] patients revealed albumin and transferrin bands only; whereas 19 steroid-resistant children with focal glomerular sclerosis showed additional excretion of IgG and low molecular weight proteins (lysozyme, beta 2-microglobulin). This mixed pattern of proteinuria was also detected in 5 other steroid-resistant patients, 3 of whom were Africans with MCNS on biopsy and 2 who were Indians and not biopsied. Findings in patients studied within 2 months of presentation were identical to those investigated later in the course of the disease. SDS PAGE analysis of urine, which appears to distinguish steroid-responsive from steroid-resistant patients may provide a valuable adjunct to the management of childhood nephrotic syndrome.

Estimation of ifosfamide/cisplatinum-induced renal toxicity by urinary protein analysis

Ifosfamide (IFO) chemotherapy has been reported to result in deToni-Debré-Fanconi syndrome in a minority of patients only, but evaluation of tubular transport capacities has identified a substantial number of patients as having subclinical tubular dysfunction. After completion of combination chemotherapy employing IFO (n = 37) or IFO plus cisplatinum (CPL) (n = 27), glomerular and tubular function was assessed in 64 patients by the urinary excretion of transferrin, IgG, albumin, alpha 1-microglobulin (A1M) and N-acetyl-beta-D-glucosaminidase. Sodium dodecyl sulphate polyacrylamide gel electrophoresis was performed in 21 patients. The determination of urinary marker proteins was compared with the glomerular filtration rate, the fractional phosphate and percent amino acid reabsorption. A reduced glomerular filtration rate was observed in 9.8% of patients. Tubular dysfunction was frequent, with a predominance of renal amino acid (57%) and A1M (48%) loss. IFO-mediated renal toxicity was dose dependent. CPL treatment resulted in significant enhancement of tubular toxicity induced by IFO, whereas concomitant gentamicin therapy did not affect tubular function. Measurement of urinary protein cannot replace other tests for tubular dysfunction in IFO-treated patients, because the spectrum of IFO-induced nephrotoxicity includes dysfunction of different and independent transport mechanisms of the proximal tubular system. Increased urinary A1M excretion is an important indicator of impaired tubular protein reabsorption.

Partial and complete de Toni-Debré-Fanconi syndrome after ifosfamide chemotherapy of childhood malignancy

Ten out of 79 patients treated with ifosfamide (IFO) developed a complete (n = 2) or partial (n = 8) de Toni-Debré-Fanconi syndrome (RFS). All but one of these patients had been treated in addition with cisplatinum (CPL) or had undergone radiotherapy to the abdomen or nephrectomy as part of the overall treatment for malignancy. A detailed nephrological work-up of proximal tubular function showed decreased fractional phosphate and percent aminoacid reabsorption in 37.1 and 56.7% of cases, respectively, and the excretion of alpha 1-microglobulin and N-acetyl-beta-D-glucosaminidase was elevated in 44.4 and 23.5%. Glomerular function was well preserved in the majority of patients. Tubular dysfunction was confirmed by silver-stained SDS PAGE of urine which showed mostly low molecular weight proteinuria. CPL has been shown to result in renal magnesium loss and reduced glomerular filtration rate, and its toxicity clearly differs from IFO-mediated tubulopathy. Our data suggest that subclinical impairment of proximal tubular function was significantly increased by additional CPL therapy. We conclude that CPL may enhance IFO-mediated nephrotoxicity and that a substantial number of patients is at risk of developing persistent tubular dysfunction leading to metabolic bone disease.