Thin basement membrane nephropathy associated with other glomerular diseases

Clinicopathological Implications of Proteinuria after Long-Term Isolated Hematuria due to Thin Basement Membrane Nephropathy and Focal Segmental Glomerulosclerosis

A 45-year-old obese man presented with persistent hematuria for 21 years. At the age of 37, he developed hypertension and proteinuria which later increased up to 1.6 g/g creatinine. Kidney biopsy revealed thin basement membrane nephropathy (TBMN) and focal segmental glomerulosclerosis (FSGS), which explained his urinary abnormalities. Although a subgroup of TBMN can be complicated by FSGS, his FSGS was associated with obesity because of its histological features. Reduction of body weight and increasing a dose of angiotensin-receptor blocker could transiently reduce the amount of proteinuria. Clinicopathological implications of proteinuria after long-term hematuria by TBMN and FSGS were further discussed.

Pathologic glomerular characteristics and glomerular basement membrane alterations in biopsy-proven thin basement membrane nephropathy

BACKGROUND

Thin basement membrane nephropathy (TBMN) is diagnosed by diffuse thinning of the glomerular basement membrane (GBM) without any clinical and pathologic findings of Alport syndrome and the other renal diseases. TBMN is characterized clinically by benign familial hematuria but rarely develops into end-stage renal disease.

METHODS

In 27 cases of biopsy-proven TBMN, we evaluated the pathologic characteristics of TBMN, and examined the correlation between these pathologic characterizations and renal dysfunction.

RESULTS

All patients had hematuria, and 21 patients (77.8%) had proteinuria. In six patients (28.6%) who were more than 50 years of age, the estimated glomerular filtration rate (eGFR) decreased from G3a to G4 in the chronic kidney disease stage. Pathologically, an irregular decrease in intensity of type IV collagen α5(IV) chain was seen in GBM, and irregular thinning with diffuse rough etched images was observed on the GBM surface with several sizes of holes by low-vacuum scanning electron microscopy. The glomerular morphology of TBMN was characterized by an increased number of small glomerular capillaries with an increased extracellular matrix (ECM). These characteristic morphologic alterations were evident from a young age in patients with TBMN, but were not correlated directly with the decrease of eGFR, the degree of hematuria, and proteinuria. The decrease of eGFR in patients with TBMN who were more than 50 years of age might be primarily mediated by arteriolosclerosis-associated glomerulosclerosis and interstitial fibrosis.

CONCLUSION

Characteristic pathological glomerular findings and GBM alterations occurred from a young age but were not associated directly with renal impairment in biopsy-proven TBMN.

Correlates of hematuria on glomerular histology and electron microscopy in IgA nephropathy

BACKGROUND

Hematuria is the most important clinical manifestation of IgA nephropathy. This study was undertaken with the objective to describe the spectrum of histological changes with reference to the Oxford classification and the ultrastructural changes in the glomerular basement membrane and to correlate them with hematuria.

METHODS

66 patients who underwent renal biopsy for IgA nephropathy were evaluated histologically by the Oxford system and also subject to electron microscopic examination for glomerular immune deposits, as well as alterations in the glomerular basement membrane.

RESULTS

On comparing the histological scores generated by the Oxford classification with degree of hematuria, it was found that the status of 'endocapillary proliferation' and the status of 'tubular atrophy and interstitial fibrosis showed a significant correlation. Correlation of hematuria with location of the deposits, i.e. mesangial only, and mesangial with capillary wall deposits (subendothelial and subepithelial) did not show any association. Other alterations of the GBM were seen in 12 cases. The changes included thinning alone in 4 cases, thinning and lamellar splitting in 5 cases, and lamellar splitting alone in 2 cases.

CONCLUSION

At presentation, endocapillary proliferation is one histological parameter which shows close association with hematuria.

Carriers of Autosomal Recessive Alport Syndrome with Thin Basement Membrane Nephropathy Presenting as Focal Segmental Glomerulosclerosis in Later Life

Collagen IV nephropathies (COL4Ns) comprise benign familial microscopic hematuria, thin basement membrane nephropathy (TBMN), X-linked Alport syndrome (AS) and also autosomal recessive and dominant AS. Apart from the X-linked form of AS, which is caused by hemizygous mutations in the COL4A5 gene, the other entities are caused by mutations in the COL4A3 or COL4A4 genes. The diagnosis of these conditions used to be based on clinical and/or histological findings of renal biopsies, but it is the new molecular genetics approach that revolutionised their investigation and proved particularly instrumental, especially, in many not so clear-cut cases. More recently, the spectrum of COL4N has expanded to include late onset focal segmental glomerulosclerosis (FSGS) that develops on top of TBMN in later life. Also, other reports showed that some patients with a primary diagnosis of familial FSGS proved to have variants in COL4 genes. In the presence of a renal biopsy picture of FSGS and in the absence of either electron microscopy studies or molecular genetic studies that point to TBMN and COL4N, the patient and his family may be mistakenly diagnosed with hereditary FSGS leading to unnecessary further investigations, erroneous family counselling and improper corticosteroid treatment. TBMN is a frequent finding in the general population, and according to several recent reports, it may be the underlying cause and the explanation for many familial and sporadic cases of late-onset FSGS with non-nephrotic proteinuria. This is an important new finding that needs widespread recognition. It is anticipated that the molecular genetic analysis with next generation sequencing will certainly offer timely correct diagnosis.

Co-existence of thin basement membrane nephropathy with other glomerular pathologies; a single center experience

Background: The co-existence of thin basement membrane nephropathy (TBMN) and another glomerular pathology portends a worse prognosis than TBMN alone.

Objectives: The purpose of our study was to investigate the prevalence of TBMN and associated glomerular pathologies at our institution.

Patients and Methods: We reviewed all renal biopsies performed at Saint Louis University hospital over a 7-year period. We excluded all post transplant biopsies, and biopsies showing diabetic glomerulopathy, membranoproliferative glomerulopathy, membranous glomerulopathy, and biopsies where no electron microscopy or immunofluorescent studies were done. All other biopsies were included.

Results: A total of 634 biopsies were included in the study. The prevalence of TBMN was 47 (7.4%), of whom 17 (36.2%) had TBMN alone. In the remaining 30 (63.8%) patients TBMN was associated with other glomerular pathologies: IgAN 9 (19.1%) and FSGS 9 (19.1%). We found significantly higher prevalence of IgAN in patients with TBMN versus all biopsies (19.1% vs. 7.7%, respectively, P = 0.002). We found significant similarities in biopsy indications for TBMN and IgAN group.

Conclusions: Around two thirds of the cases of TBMN were associated with other glomerular pathologies. The prevalence of IgAN, but not focal segmental glomerulosclerosis, was significantly higher in patients with TBMN as compared to the general renal biopsy specimens.

Molecular genetics of familial hematuric diseases

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.

Clinical manifestations of IgA nephropathy combined with thin glomerular basement membrane nephropathy in children

Background

Immunoglobulin A nephropathy (IgAN) and thin glomerular basement membrane nephropathy (TBMN) are the most common causes of persistent hematuria during childhood. The objective of this study is to determine the difference in clinical features and laboratory findings between pediatric patients with IgA deposited TBMN and IgAN alone.

Methods

Between January 2000 and March 2009, 95 children were diagnosed with IgAN by renal biopsy. Clinical features and laboratory findings of patients with isolated IgAN and with IgAN plus TBMN were compared; the children diagnosed with IgAN were compared to 127 children who had been diagnosed with TBMN alone during the same period.

Results

There were 71 (74.7%) of a total 95 patients that were diagnosed with isolated IgAN (Group1); in 24 (25.3%) of the 95 patients IgAN was combined with TBMN (Group 2). There was marked difference in the gender distribution between Group 2 and isolated TBMN patients. The degree of proteinuria and pathologic severity was higher in Group 1 compared with Group 2. Gross hematuria was present in both groups. There were no distinguishing features in the other laboratory parameters.

Conclusion

Patients with both IgAN and TBMN seem to have similar clinical features to patients with isolated IgAN; however, the latter tend to have better pathologic and laboratory findings, compared to the patients with IgAN alone.

The role of molecular genetics in diagnosing familial hematuria(s)

Familial microscopic hematuria (MH) of glomerular origin represents a heterogeneous group of monogenic conditions involving several genes, some of which remain unknown. Recent advances have increased our understanding and our ability to use molecular genetics for diagnosing such patients, enabling us to study their clinical characteristics over time. Three collagen IV genes, COL4A3, COL4A4, and COL4A5 explain the autosomal and X-linked forms of Alport syndrome (AS), and a subset of thin basement membrane nephropathy (TBMN). A number of X-linked AS patients follow a milder course reminiscent of that of patients with heterozygous COL4A3/COL4A4 mutations and TBMN, while at the same time a significant subset of patients with TBMN and familial MH progress to chronic kidney disease (CKD) or end-stage kidney disease (ESKD). A mutation in CFHR5, a member of the complement factor H family of genes that regulate complement activation, was recently shown to cause isolated C3 glomerulopathy, presenting with MH in childhood and demonstrating a significant risk for CKD/ESKD after 40 years old. Through these results molecular genetics emerges as a powerful tool for a definite diagnosis when all the above conditions enter the differential diagnosis, while in many at-risk related family members, a molecular diagnosis may obviate the need for another renal biopsy.

COL4A3 founder mutations in Greek-Cypriot families with thin basement membrane nephropathy and focal segmental glomerulosclerosis dating from around 18th century

Mutations in the COL4A3/COL4A4 genes of type IV collagen account for about 40% of cases of thin basement membrane nephropathy, a condition that is estimated to affect 1% or more of the general population. We recently described 10 Cypriot families with familial hematuria and thin basement membrane nephropathy in the presence of focal segmental glomerulosclerosis, with founder mutations on COL4A3 gene. Seven of the families carried mutation G1334E on haplotype K, and another three carried mutation G871C on haplotype Ky. In this report we performed extension of the haplotypes with additional polymorphic markers, 12 for haplotype K and 22 for haplotype Ky, to estimate the linkage disequilibrium value between the mutation and flanking noncommon markers. Haplotype Ky extended to 13.71 Mb, but we did not attempt further analysis owing to the small number of chromosomes. Haplotype K extended to 3.83 Mb, thereby suggesting that it was a much older event compared to mutation G871C. Mutation G1334E was calculated to be about 5-10 generations old with a possible origin between 1693 and 1818 AD, during the Ottoman ruling of the island. Both mutations are clustered in specific geographic regions with apparently formerly isolated populations, although mutation G1334E has been detected elsewhere on the island. The identification of founder mutations in large families with microscopic hematuria greatly facilitates presymptomatic diagnosis and provides useful information on the history of the population, while it may also assist in association studies in search for disease modifier genes.

COL4A3/COL4A4 mutations producing focal segmental glomerulosclerosis and renal failure in thin basement membrane nephropathy

Mutations in the COL4A3/COL4A4 genes of type IV collagen have been found in approximately 40% of cases of thin basement membrane nephropathy, which is characterized by microscopic hematuria and is classically thought to cause proteinuria and chronic renal failure rarely. Here we report our observations of 116 subjects from 13 Cypriot families clinically affected with thin basement membrane nephropathy. These families first came to our attention because they segregated microscopic hematuria, mild proteinuria, and variable degrees of renal impairment, but a dual diagnosis of focal segmental glomerulosclerosis (FSGS) and thin basement membrane nephropathy was made in 20 biopsied cases. Molecular studies identified founder mutations in both COL4A3 and COL4A4 genes in 10 families. None of 82 heterozygous patients had any extrarenal manifestations, supporting the diagnosis of thin basement membrane nephropathy. During follow-up of up to three decades, 31 of these 82 patients (37.8%) developed chronic renal failure and 16 (19.5%) reached end-stage renal disease. Mutations G1334E and G871C were detected in seven and three families, respectively, and were probably introduced by founders. We conclude that these particular COL4A3/COL4A4 mutations either predispose some patients to FSGS and chronic renal failure, or that thin basement membrane nephropathy sometimes coexists with another genetic modifier that is responsible for FSGS and progressive renal failure. The findings presented here do not justify the labelling of thin basement membrane nephropathy as a benign condition with excellent prognosis.

Pattern of double glomerulopathy in children

Occasional case reports have been issued on children with double glomerulopathy, involving either the coexistence of two different glomerulopathies or superimposition of a second glomerulopathy onto a first. A retrospective clinicopathological review of 294 children who had received renal biopsies resulted in 9 (3.1%) being confirmed to have double glomerulopathy. Superimposed glomerulopathy was diagnosed by a second renal biopsy in two cases, and coexistence of two glomerulopathies was confirmed by single biopsy in seven. Original glomerulopathies were those with a chronic course, such as Alport syndrome, IgA nephropathy, relapsing minimal-change nephrotic syndrome, Frasier syndrome, and thin basement membrane nephropathy. The superimposing glomerulopathies were common types in children, such as postinfectious glomerulonephritis, IgA nephropathy, and Henoch-Schönlein nephritis. Thus, the pattern of double glomerulopathy was considered to be due to the chance occurrence of two different glomerulopathies without a common pathogenesis. Acute nephritic symptoms of superimposed glomerulopathies resolved almost completely during follow-up in most cases. Double glomerulopathies are not rare in children and may occur by chance alone in most cases. The possibility of superimposed glomerulopathy should be suspected if the clinical course of a glomerulopathy changes atypically. However, the long-term influence of a superimposed glomerulopathy on renal functional deterioration remains unclear.

Chronic renal failure and shortened lifespan in COL4A3+/- mice: an animal model for thin basement membrane nephropathy

A heterozygous mutation in autosomal Alport genes COL4A3 and COL4A4 can be found in 20 to 50% of individuals with familial benign hematuria and diffuse glomerular basement membrane thinning (thin basement membrane nephropathy [TBMN]). Approximately 1% of humans are heterozygous carriers of mutations in the autosomal Alport genes and at risk for developing renal failure as a result of TBMN. The incidence and pathogenesis of renal failure in heterozygous COL4A3/4 mutation carriers is still unclear and was examined further in this study using COL4A3 knockout mice. In heterozygous COL4A3(+/-) mice lifespan, hematuria and renal function (serum urea and proteinuria) were monitored during a period of 3 yr, and renal tissue was examined by light and electron microscopy, immunohistochemistry, and Western blot. Lifespan of COL4A3(+/-) mice was found to be significantly shorter than in healthy controls (21.7 versus 30.3 mo). Persistent glomerular hematuria was detected starting in week 9; proteinuria of > 0.1 g/L started after 3 mo of life and increased to > 3 g/L after 24 mo. The glomerular basement membrane was significantly thinned (167 versus 200 nm in wild type) in 30-wk-old mice, coinciding with focal glomerulosclerosis, tubulointerstitial fibrosis, and increased levels of TGF-beta and connective tissue growth factor. The renal phenotype in COL4A3(+/-) mice resembled the clinical and histopathologic phenotype of human cases of TBMN with concomitant progression to chronic renal failure. Therefore, the COL4A3(+/-) mouse model will help in the understanding of the pathogenesis of TBMN in humans and in the evaluation of potential therapies.

Thin basement membrane nephropathy associated with minimal change disease in a 15-year-old boy

Thin basement membrane nephropathy (TBMN) is characterized clinically by persistent hematuria, minimal proteinuria, normal renal function, another family member with hematuria, and a benign course. Especially in childhood TBMN, proteinuria of any degree is reported to be uncommon. We report on a boy with benign familial hematuria found by urinary screening at 3 years of age who presented with nephrotic syndrome (NS) at 15 years of age. His renal histology showed TBMN associated with minimal change disease (MCD). Treatment with corticosteroid resulted in complete remission of NS in a short period of time, while isolated hematuria persisted during the follow-up period despite this therapy. We speculate, therefore, that the nephrotic range proteinuria is not due to TBMN but rather is the manifestation of associated MCD. Several cases of TBMN with NS have been reported in adults, but it has not yet been reported in children in the literature. To our knowledge, this is the first case of childhood TBMN associated with NS resulting from coincidental MCD.