Thin glomerular basement membrane nephropathy: incidence in 3471 consecutive renal biopsies examined by electron microscopy.
ABSTRACT Thin glomerular basement membrane (GBM) nephropathy is often equated with benign familial hematuria, although it may occur sporadically and may not always be benign. Thin GBM nephropathy is reported to occur in at least 1% of the population, although its reported incidence varies considerably in different studies because there are presently no uniform criteria for its diagnosis by electron microscopy (EM).
To determine the incidence of thin GBM nephropathy in a large sample of renal biopsies using a basic methodology that can easily be applied in any diagnostic EM laboratory.
Direct measurements of GBM thickness were made from electron micrographs at 3 specified points along each of 10 randomly selected glomerular capillaries to determine an average GBM thickness for each of 50 males and 50 females, ages 9 to 80 years, with minimal-change nephropathy or acute interstitial nephritis, without hematuria. The means of the average GBM thickness values were 330 +/- 50 (SD) nm in the males and 305 +/- 45 nm in the females; normal ranges for each sex were defined as being within 2 SD of these means. The average GBM thickness was then similarly determined for renal biopsies with suspected thin GBMs examined from January 2000 to December 2004; a total of 3471 renal biopsies were examined by EM during this period.
Academic medical center renal pathology/EM laboratory.
Excluding biopsies with immunoglobulin A nephropathy, which is known to be frequently associated with thin GBMs, and biopsies with Alport syndrome, 67 biopsies (1.9% of total) had an average GBM thickness below the sex-specific normal range. Of these, 37 biopsies were performed specifically because of hematuria and had an average GBM thickness of 121 to 215 nm (mean, 185 +/- 20 nm). The remaining 30 (0.9%) biopsies, with average GBM thicknesses of 143 to 227 nm (mean, 190 +/- 20 nm), represent cases of incidentally discovered thin GBM nephropathy.
Based on the frequency of incidentally discovered cases and taking into account excluded cases and biopsies (eg, with diabetic nephropathy) in which diagnosis of incidental thin GBM nephropathy by EM is not possible, the incidence of thin GBM nephropathy in our population is estimated to be between 1% and 2%. Diseases most often associated with incidental thin GBM nephropathy were focal segmental glomerulosclerosis (10 cases) and minimal-change nephropathy (5 cases).
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ABSTRACT: Focal segmental glomerulosclerosis (FSGS) is a histological lesion with many causes, including inherited genetic defects, with significant proteinuria being the predominant clinical finding at presentation. Mutations in COL4A3 and COL4A4 are known to cause Alport syndrome (AS), thin basement membrane nephropathy, and to result in pathognomonic glomerular basement membrane (GBM) findings. Secondary FSGS is known to develop in classic AS at later stages of the disease. Here, we present seven families with rare or novel variants in COL4A3 or COL4A4 (six with single and one with two heterozygous variants) from a cohort of 70 families with a diagnosis of hereditary FSGS. The predominant clinical finding at diagnosis was proteinuria associated with hematuria. In all seven families, there were individuals with nephrotic-range proteinuria with histologic features of FSGS by light microscopy. In one family, electron microscopy showed thin GBM, but four other families had variable findings inconsistent with classical Alport nephritis. There was no recurrence of disease after kidney transplantation. Families with COL4A3 and COL4A4 variants that segregated with disease represent 10% of our cohort. Thus, COL4A3 and COL4A4 variants should be considered in the interpretation of next-generation sequencing data from such patients. Furthermore, this study illustrates the power of molecular genetic diagnostics in the clarification of renal phenotypes.Kidney International advance online publication, 17 September 2014; doi:10.1038/ki.2014.305.Kidney International 09/2014; DOI:10.1038/ki.2014.305 · 8.52 Impact Factor
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ABSTRACT: The familial hematuric diseases are a genetically heterogeneous group of monogenic conditions, caused by mutations in one of several genes. The major genes involved are the following: (i) the collagen IV genes COL4A3/A4/A5 that are expressed in the glomerular basement membranes (GBM) and are responsible for the most frequent forms of microscopic hematuria, namely Alport syndrome (X-linked or autosomal recessive) and thin basement membrane nephropathy (TBMN). (ii) The FN1 gene, expressed in the glomerulus and responsible for a rare form of glomerulopathy with fibronectin deposits (GFND). (iii) CFHR5 gene, a recently recognized regulator of the complement alternative pathway and mutated in a recently revisited form of inherited C3 glomerulonephritis (C3GN), characterized by isolated C3 deposits in the absence of immune complexes. A hallmark feature of all conditions is the age-dependent penetrance and a broad phenotypic heterogeneity in the sense that subsets of patients progress to added proteinuria or proteinuria and chronic renal failure that may or may not lead to end-stage kidney disease (ESKD) anywhere between the second and seventh decade of life. In addition to other excellent laboratory tools that assist the clinician in reaching the correct diagnosis, the molecular analysis emerges as the gold standard in establishing the diagnosis in many cases of doubt due to equivocal findings that complicate the differential diagnosis. Recent work led to the description of candidate genetic modifiers which confer a variable risk for progressing to chronic renal failure when co-inherited on the background of a primary glomerulopathy. Finally, more families are still waiting to be studied and more genes to be mapped and cloned that are responsible for other forms of heritable hematuric diseases. The study of such genes and their protein products will likely shed more light on the structure and function of the glomerular filtration barrier and other important glomerular components.Nephrology Dialysis Transplantation 09/2013; DOI:10.1093/ndt/gft253 · 3.49 Impact Factor
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ABSTRACT: Aims The kidneys of patients with diabetes mellitus usually exhibit a characteristic pattern of linear immunofluorescent staining for immunoglobulin G (IgG) along the glomerular and tubular basement membranes. However, the association between linear IgG staining and the renal prognosis remains unclear. Methods Among 223 patients with diabetes who underwent renal biopsy from 1985 to 2010 and were confirmed to have pure diabetic nephropathy according to the classification of Tervaert et al., 165 patients (glomerular classes I to III) were enrolled in this study. Immunofluorescent staining was classified into three categories according to its intensity (0 = none, 1 = weakly positive, and 2 = positive). Cox proportional hazards regression analysis was used to calculate the hazard ratio (HR) and 95% confidence interval (CI) for death-censored renal death, with each regression analysis employing four levels of multivariate adjustment. Results After adjustment for important clinical factors at the time of renal biopsy, the HR for death-censored renal death in patients with an IgG staining score of 1 or 2 was respectively 3.01 (95% CI: 1.05-8.68) and 4.68 (1.67-13.1) compared with patients who had a staining score of 0. Even after adjustment for clinical variables and pathological findings, the HR for IgG score of 1 or 2 was higher than that for an IgG score of 0, and it was respectively 2.22 (0.71-7.00) and 3.76 (1.27-11.2). Conclusions More intense linear IgG staining is associated with a higher HR for renal death, which suggests that linear immunofluorescent staining for IgG may be a prognostic indicator in patients with diabetic nephropathy.Diabetes Research and Clinical Practice 10/2014; 106(3). DOI:10.1016/j.diabres.2014.09.051 · 2.54 Impact Factor