Glomerular basement membrane and lamina densa in infants and children: an ultrastructural evaluation

3D Mapping Reveals a Complex and Transient Interstitial Matrix During Murine Kidney Development

BACKGROUND

The extracellular matrix (ECM) is a network of proteins and glycosaminoglycans that provides structural and biochemical cues to cells. In the kidney, the ECM is critical for nephrogenesis; however, the dynamics of ECM composition and how it relates to 3D structure during development is unknown.

METHODS

Using embryonic day 14.5 (E14.5), E18.5, postnatal day 3 (P3), and adult kidneys, we fractionated proteins based on differential solubilities, performed liquid chromatography-tandem mass spectrometry, and identified changes in ECM protein content (matrisome). Decellularized kidneys were stained for ECM proteins and imaged in 3D using confocal microscopy.

RESULTS

We observed an increase in interstitial ECM that connects the stromal mesenchyme to the basement membrane (TNXB, COL6A1, COL6A2, COL6A3) between the embryo and adult, and a transient elevation of interstitial matrix proteins (COL5A2, COL12A1, COL26A1, ELN, EMID1, FBN1, LTBP4, THSD4) at perinatal time points. Basement membrane proteins critical for metanephric induction (FRAS1, FREM2) were highest in abundance in the embryo, whereas proteins necessary for integrity of the glomerular basement membrane (COL4A3, COL4A4, COL4A5, LAMB2) were more abundant in the adult. 3D visualization revealed a complex interstitial matrix that dramatically changed over development, including the perinatal formation of fibrillar structures that appear to support the medullary rays.

CONCLUSION

By correlating 3D ECM spatiotemporal organization with global protein abundance, we revealed novel changes in the interstitial matrix during kidney development. This new information regarding the ECM in developing kidneys offers the potential to inform the design of regenerative scaffolds that can guide nephrogenesis in vitro.

Insights into the renal pathogenesis in Schimke immuno-osseous dysplasia: A renal histological characterization and expression analysis

Schimke immuno-osseous dysplasia (SIOD) is a pleiotropic disorder caused by mutations in the SWI/SNF2-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like-1 (SMARCAL1) gene, with multiple clinical features, notably end-stage renal disease. Here we characterize the renal pathology in SIOD patients. Our analysis of SIOD patient renal biopsies demonstrates the tip and collapsing variants of focal segmental glomerulosclerosis (FSGS). Additionally, electron microscopy revealed numerous glomerular abnormalities most notably in the podocyte and Bowman's capsule. To better understand the role of SMARCAL1 in the pathogenesis of FSGS, we defined SMARCAL1 expression in the developing and mature kidney. In the developing fetal kidney, SMARCAL1 is expressed in the ureteric epithelium, stroma, metanephric mesenchyme, and in all stages of the developing nephron, including the maturing glomerulus. In postnatal kidneys, SMARCAL1 expression is localized to epithelial tubules of the nephron, collecting ducts, and glomerulus (podocytes and endothelial cells). Interestingly, not all cells within the same lineage expressed SMARCAL1. In renal biopsies from SIOD patients, TUNEL analysis detected marked increases in DNA fragmentation. Our results highlight the cells that may contribute to the renal pathogenesis in SIOD. Further, we suggest that disruptions in genomic integrity during fetal kidney development contribute to the pathogenesis of FSGS in SIOD patients.

Laminations and microgranule formation in pediatric glomerular basement membranes

Glomerular basement membrane (GBM) splitting, laminations, and microgranular formation are classically encountered with Alport disease, but can be found in other glomerular diseases. We found moderate to marked GBM laminations/microgranular formations in 51 of 724 (7%) pediatric diagnostic renal biopsies. These included 12 Alport disease, 12 thin basement membrane disease (TBM), 13 mesangial hypercellularity (MH), 6 focal segmental glomerulosclerosis (FSGS), and 8 other diseases. Follow-up demonstrated progression in most of the Alport disease and FSGS, as expected, but also in 40% of TBM and 30% of MH. Basement membrane laminations/microgranular formations are not specific for Alport disease, may represent a non-specific injury, and may herald a progressive clinical course.

Nephrotic-range proteinuria in an infant with thin basement membrane nephropathy

Thin basement membrane nephropathy (TBMN) with heterozygous COL4A3/COL4A4 mutations is considered to be a cause of benign familial hematuria. The disease has been believed to have excellent prognosis and TBMN in early childhood is rarely associated with nephrotic-range proteinuria. Furthermore, the presence of proteinuria in patients with TBMN is associated with autosomal-dominant Alport syndrome, which has poorer prognosis in later life. We present an infant case of nephrotic-range proteinuria associated with TBMN caused by heterozygous COL4A4 mutation. A previously healthy 3-year-old boy developed microhematuria and nephrotic-range proteinuria. Renal pathology simply revealed thinning of the glomerular basement membrane (GBM) and mutational analysis revealed a novel heterozygous mutation in COL4A4. He was treated with lisinopril for 1.5 years, which resolved his proteinuria and hematuria. At the most recent follow-up at 6.5 years of age, urinalysis and kidney function were completely normal, without requiring medication. However, transient but repeated moderate to nephrotic-range proteinuria and microscopic hematuria occurred in association with other illnesses. This case highlights the spectrum of phenotypes that may be apparent in an infant with TBMN. Thinning of the GBM can cause transient nephrotic-range proteinuria, particularly in the early stages of TBMN.

Validation of glomerular basement membrane thickness changes with aging in minimal change disease

Measurement of the normal range of glomerular basement membrane (GBM) thickness by electron microscopy is required for the diagnosis of thin basement membrane disease or diabetic nephropathy; however, this measurement is influenced by aging. The aim of this study was to introduce a simple histogram plotting method for the validation of the results of the GBM thickness measurements by the accepted arithmetic mean ± SD method. We examined renal biopsy specimens obtained from 19 patients (10 males and 9 females) with minimal change disease, ranging in age from 3 to 70 years. Renal tissue samples obtained at autopsy from a male baby (3 months old) with no renal disease were also examined. For each case, GBM thicknesses at 10-15 evenly distributed points per glomerular loop were directly measured and the arithmetic mean ± SD was calculated. Subsequently, the arithmetic mean ± SD for each group of cases classified by age into 4 groups, i.e. babyhood (3 months old), childhood (3-11 years old), adulthood (12-57 years old), and old age (60-70 years old), was determined. On the other hand, a histogram of the frequency of GBM points measured against thickness was plotted to determine the distribution pattern and the range of measurements in each age group. The histogram plot showed 4 clearly divided modes for GBM thickness. Comparison of the results obtained by the 2 methods revealed a significant correlation indicating the feasibility of the histogram plotting method as a useful adjunct to validate GBM thickness measurements.

The natural progression of kidney injury in young type 1 diabetic patients

Diabetes is the most common cause of end-stage renal disease in industrialized countries. This article describes the structural changes in early diabetic nephropathy and the relationship with renal functional parameters, blood pressure, and albumin excretion. The detrimental influence of sustained hyperglycemia and/or glycemic fluctuations on renal structural change has been well documented. Tight glycemic control is paramount to preventing the development, and even the regression, of renal lesions. As much of the renal injury from diabetes occurs in clinical silence before symptoms or laboratory findings of renal injury are evident, finding early markers of risk is imperative so that nephropathy can be prevented. Currently, the only clinical surrogate marker of diabetic renal injury available is microalbuminuria. However, given the reports of regression of microalbuminuria back to normoalbuminuria, the reliability of this tool as an indicator of risk has been questioned. The need for alternative, noninvasive surrogate markers is described in this report.

Alport syndrome and thin glomerular basement membrane nephropathy: a practical approach to diagnosis

CONTEXT

Alport syndrome and thin glomerular basement membrane nephropathy (TBMN) are genetically heterogeneous conditions characterized by structural abnormalities in the glomerular basement membrane and an initial presentation that usually involves hematuria. Approximately 40% of patients with TBMN are heterozygous carriers for autosomal recessive Alport syndrome, with mutations at the genetic locus encoding type IV collagen alpha(3) [alpha(3)(IV)] and alpha(4) chains. However, although the clinical course of TBMN is usually benign, Alport syndrome, particularly the X-linked form with mutations in the locus encoding the alpha(5) chain of type IV collagen [alpha(5)(IV)], typically results in end-stage renal disease. Electron microscopy is essential to diagnosis of TBMN and Alport syndrome on renal biopsy, although electron microscopy alone is of limited value in distinguishing between TBMN, the heterozygous carrier state of X-linked Alport syndrome, autosomal recessive Alport syndrome, and even early stages of X-linked Alport syndrome.

OBJECTIVES

To review diagnostic pathologic features of each of the above conditions, emphasizing the need for immunohistology for alpha(3)(IV) and alpha(5)(IV) in addition to electron microscopy to resolve this differential diagnosis on a renal biopsy. The diagnostic value of immunofluorescence studies for alpha(5)(IV) on a skin biopsy in family members of patients with Alport syndrome also is reviewed.

DATA SOURCES

Original and comprehensive review articles on the diagnosis of Alport syndrome and TBMN from the past 35 years, primarily the past 2 decades, and experience in our own renal pathology laboratory.

CONCLUSIONS

Although Alport syndrome variants and TBMN do not show characteristic light microscopic findings and can be difficult to differentiate from each other even by electron microscopy, using a combination of electron microscopy and immunohistology for alpha(3)(IV) and alpha(5)(IV) enables pathologists to definitively diagnose these disorders on renal biopsy in most cases.

Hereditary nephritis mimicking immune complex-mediated glomerulonephritis

The defining ultrastructural features of hereditary nephritis are "basket weave" lamellation or thinning of glomerular basement membranes. Electron-dense deposits are not seen and immunofluorescence (IF) is generally negative. In this study, we report 5 cases of hereditary nephritis in which substantial amounts of glomerular electron-dense deposits were identified on electron microscopy, with corresponding positive IF staining in 4 cases, suggesting immune complex-mediated glomerulonephritis. However, no case had histological evidence of glomerular endocapillary or extracapillary proliferation or leukocyte infiltration typical of active glomerulonephritis. Four cases were diagnosed at outside institutions simply as forms of glomerulonephritis without considering the possibility of hereditary nephritis and were sent for consultation in contemplation of possible immunosuppressive therapy. All patients had negative serologies and no known underlying infectious or autoimmune disease; 4 patients had family history of hematuria or renal disease. The glomerular electron-dense deposits were predominantly mesangial (4 cases) and intramembranous (4 cases), as well as subepithelial (2 cases) or subendothelial (1 case). Corresponding IF positivity for immune reactants was identified in 4 cases, and IgG was the predominant immunoglobulin deposited. A characteristic feature was the tendency for deposits to form between the complex layers of glomerular basement membrane material, favoring a process of nonspecific entrapment of immune reactants within the thickened, lamellated basement membrane. In all cases, a diagnosis of hereditary nephritis was confirmed by demonstration of the characteristic loss of immunoreactivity for the alpha5 subunit of collagen IV (4 cases) or Goodpasture's antigen (1 case) in renal or epidermal basement membranes. These cases expand the spectrum of unusual pathological findings in hereditary nephritis and emphasize the potential for hereditary nephritis to mimic immune complex glomerulonephritis.

Thin glomerular basement membrane nephropathy: incidence in 3471 consecutive renal biopsies examined by electron microscopy

CONTEXT

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).

OBJECTIVE

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.

DESIGN

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.

SETTING

Academic medical center renal pathology/EM laboratory.

RESULTS

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.

CONCLUSIONS

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).

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.

Thin basement membrane nephropathy

Thin basement membrane nephropathy. Thin basement membrane nephropathy (TBMN) is the most common cause of persistent glomerular bleeding in children and adults, and occurs in at least 1% of the population. Most affected individuals have, in addition to the hematuria, minimal proteinuria, normal renal function, a uniformly thinned glomerular basement membrane (GBM) and a family history of hematuria. Their clinical course is usually benign. However, some adults with TBMN have proteinuria >500 mg/day or renal impairment. This is more likely in hospital-based series of biopsied patients than in the uninvestigated, but affected, family members. The cause of renal impairment in TBMN is usually not known, but may be due to secondary focal segmental glomerulosclerosis (FSGS) or immunoglobulin A (IgA) glomerulonephritis, to misdiagnosed IgA disease or X-linked Alport syndrome, or because of coincidental disease. About 40% families with TBMN have hematuria that segregates with the COL4A3/COL4A4 locus, and many COL4A3 and COL4A4 mutations have now been described. These genes are also affected in autosomal-recessive Alport syndrome, and at least some cases of TBMN represent the carrier state for this condition. Families with TBMN in whom hematuria does not segregate with the COL4A3/COL4A4 locus can be explained by de novo mutations, incomplete penetrance of hematuria, coincidental hematuria in family members without COL4A3 or COL4A4 mutations, and by a novel gene locus for TBMN. A renal biopsy is warranted in TBMN only if there are atypical features, or if IgA disease or X-linked Alport syndrome cannot be excluded clinically. In IgA disease, there is usually no family history of hematuria. X-linked Alport syndrome is much less common than TBMN and can often be identified in family members by its typical clinical features (including retinopathy), a lamellated GBM without the collagen alpha3(IV), alpha4(IV), and alpha5(IV) chains, and by gene linkage studies or the demonstration of a COL4A5 mutation. Technical difficulties in the demonstration and interpretation of COL4A3 and COL4A4 mutations mean that mutation detection is not used routinely in the diagnosis of TBMN.

Glomerular basement membrane thickness in children: a stereologic assessment

BACKGROUND

Stereologic methods have emerged as the technique of choice in assessing glomerular basement membrane (GBM) thickness, following conceptual modeling comparing the stereologic technique of harmonic mean of the orthogonal intercept estimation (Th) with the model based method of arithmetic mean estimation (ATH), with no direct comparison undertaken. We undertook to establish the gold standard for GBM estimation and use this technique to establish a range for GBM thickness in children.

METHODS

Intra-observer and inter-glomerular variation was estimated in 34 cases with (presumed) normal GBM thickness, using Th, ATH and a rapid direct measurement technique, with intra-observer variation measured in 35 cases with GBM attenuation. A total of 34,011 measurements were undertaken to establish a range for Th in children on 212 biopsies from 199 patients (127 male) demonstrating minimal change nephropathy (N = 153), focal segmental glomerulosclerosis (24), no abnormality (24), and acute tubular necrosis (8), which were used as surrogates for normals.

RESULTS

Th demonstrated less variation than ATH in both the normal and attenuated groups. GBM thickness increased throughout childhood, from 194 +/- 6.5 nm (mean +/- SE) at one year to 297 +/- 6.0 nm at 11 years, with a reduced rate of increase after age 11 years.

CONCLUSION

Stereologic methods are superior to model based techniques in estimating GBM thickness and should be regarded as the technique of choice in this area. GBM thickness was observed to increase during childhood with no gender effect demonstrable as a main effect or interaction.

Histopathology, ultrastructure, and clinical phenotypes in thin glomerular basement membrane disease variants

Recent genetic studies indicate that Alport syndrome and thin glomerular basement membrane disease (TMD) may both be due to COL4A3, COL4A4, and COL4A5 mutations, but there is continuing uncertainty concerning the diagnosis and management of patients without classic family history and symptoms. We examined kidney pathology and collagen alpha 3 to alpha 5(IV) expression in a series of 16 patients who presented with overlapping signs between TMD and Alport nephritis. All patients presented with hematuria, and 11 also had proteinuria, of whom 5 had nephrotic range proteinuria. Only 9 had family history of hematuria. In 9 of 16 (60%) we found premature glomerulosclerosis in the renal biopsies. Three of 16 had predominantly wide, lamellated glomerullar basement membranes (GBM), and in these, alpha 3 to alpha 5(IV) was absent in glomeruli or skin, diagnostic of Alport nephritis. One patient (12) had a very wide GBM with intramembranous lucencies but no lamellation. Skin biopsy was collagen alpha 5(IV) positive. Nine of 16 patients had predominantly thin GBM by electron microscopy, and 3 had thin and slightly lamellated GBM. Collagen alpha 3 to alpha 5(IV) expression in the kidney or skin biopsy was present in all of the latter 12 patients. Three patients had end-stage renal disease, 7 patients had hypertension, and 1 patient had chronic renal failure. We found that of the 16 patients with presumed TMD, 3 had X-linked Alport nephritis, 2 appeared to have autosomal recessive Alport nephritis, and the remaining patients had either an Alport or a TMD variant. The latter had histologic and/or clinical evidence of progressive renal disease, including premature glomerulosclerosis, hypertension, sustained proteinuria, and either thin or slight GBM lamellation focally, and preserved alpha 3 to alpha 5(IV) expression. These patients have a TMD variant, but an Alport variant with a potentially transmissible severe defect different from benign hematuria cannot be excluded.

Alport disease: a review of the diagnostic difficulties

In patients with familial hematuria, ultrastructural study of the renal biopsy has been the gold standard for the diagnosis of Alport disease, based on characteristic findings of glomerular basement membrane thickening due to reduplication of the lamina densa. But the diagnosis has difficulties as not all biopsies from Alport disease patients have these structural changes. In adult female patients or in children, extensive thinning of the basement membrane can be the major abnormality by electron microscopy. Until the genetic mutation of collagen IV responsible for Alport disease can be demonstrated in all patients, the diagnosis will continue to be a challenge at the clinical and at the ultrastructural levels.

Distribution of alpha-chains of type IV collagen in glomerular basement membranes with ultrastructural alterations suggestive of Alport syndrome

BACKGROUND

In Alport syndrome (AS) impaired production and/or assembly of col IV alpha-chain isoforms results in abnormal structure of glomerular basement membrane (GBM), haematuria and, frequently, progressive renal disease. We investigated the relationship between col IV alpha-chains expression and morphology of GBM, as a possible key to the better understanding of the pathogenesis of renal disease in AS.

METHODS

GBM distribution of col IV alpha1-, alpha3-, and alpha5-chain was investigated by immunohistochemistry in 32 patients (21 males and 11 females, mean age at biopsy of 11.5 years) with ultrastructural findings suggestive of AS. Ten patients had a proven COL4A5 mutation. Based on the severity of ultrastructural findings, the biopsies were grouped in three (I-III) electron microscopy (EM) classes. Significant EM changes of GBM (thinning, thickening, splitting, basket weaving of the lamina densa) were singularly evaluated using a semiquantitative scale (0-3).

RESULTS

Col IV alpha1-chain was demonstrated in GBM of all patients. Three patterns of staining for col IValpha3- and alpha5-chains were observed: positive, negative, and alpha3(IV)-positive/alpha5(IV)-negative. By chi(2)-test, EM class III lesions and complete loss of alpha3(IV)- and alpha5(IV)-antigen were significantly more frequent (P<0.05 and P<0.01) in male patients, but no significant relation was observed between EM classes and immunohistochemical patterns. GBM alterations did not correlate with staining for alpha5(IV)-chain. Intensity of alpha3(IV)-chain staining, however, had a negative correlation (P<0.05) with the severity of GBM basket weaving.

CONCLUSIONS

Our results suggest that the alpha3(IV)-chain-containing col IV-network plays a fundamental role in structural and, possibly, functional organization of GBM. Absence of alpha3(IV)-chain in GBM could indicate a more severe renal disease in AS.

Segregation of hematuria in thin basement membrane disease with haplotypes at the loci for Alport syndrome

BACKGROUND

Inherited hematuria is common and is usually attributed to thin basement membrane disease (TBMD). The aim of this study was to determine how often hematuria in families with TBMD segregated with haplotypes at the chromosomal loci for autosomal recessive and X-linked Alport syndrome (COL4A3/COL4A4 and COL4A5, respectively).

METHODS

The families of 22 individuals with TBMD on renal biopsy and with urinary glomerular red blood cell (RBC) counts of more than 50,000/mL were studied using phase-contrast microscopy of the urine and DNA microsatellite markers. Eighteen families had at least two members with hematuria.

RESULTS

Hematuria segregated with or was consistent with segregation at the COL4A3/COL4A4 locus in eight (36%) families (P < 0.05 in 5 of these) and at the COL4A5 locus in four (18%) families (P < 0.05 in 2). The lack of segregation in the other 10 (45%) families may have occurred because of incomplete penetrance of the hematuria, de novo mutations, coincidental hematuria in other family members, or the presence of a novel gene locus. In four different families, three of which had hematuria that segregated with the COL4A3/COL4A4 locus, four family members with the hematuria haplotype had spouses with coincidental hematuria (4 of 29, 14%). However, none of their four offspring who had also inherited the hematuria haplotype had the clinical features of autosomal recessive Alport syndrome.

CONCLUSIONS

Hematuria in families with TBMD commonly segregates with the COL4A3/COL4A4 locus and thus results from mutations in the same genes as autosomal recessive Alport syndrome. Sometimes TBMD may be confused with the carrier state for X-linked Alport syndrome. However, nearly half of the families in this study had hematuria that did not segregate with the loci for either autosomal recessive or X-linked Alport syndrome.

Alport syndrome. An inherited disorder of renal, ocular, and cochlear basement membranes

Alport syndrome (AS) is a genetically heterogeneous disease arising from mutations in genes coding for basement membrane type IV collagen. About 80% of AS is X-linked, due to mutations in COL4A5, the gene encoding the alpha 5 chain of type IV collagen (alpha 5[IV]). A subtype of X-linked Alport syndrome (XLAS) in which diffuse leiomyomatosis is an associated feature reflects deletion mutations involving the adjacent COL4A5 and COL4A6 genes. Most other patients have autosomal recessive Alport syndrome (ARAS) due to mutations in COL4A3 or COL4A4, which encode the alpha 3(IV) and alpha 4(IV) chains, respectively. Autosomal dominant AS has been mapped to chromosome 2 in the region of COL4A3 and COL4A4. The features of AS reflect derangements of basement membrane structure and function resulting from changes in type IV collagen expression. The primary pathologic event appears to be the loss from basement membranes of a type IV collagen network composed of alpha 3, alpha 4, and alpha 5(IV) chains. While this network is not critical for normal glomerulogenesis, its absence appears to provoke the overexpression of other extracellular matrix proteins, such as the alpha 1 and alpha 2(IV) chains, in glomerular basement membranes, leading to glomerulosclerosis. The diagnosis of AS still relies heavily on histologic studies, although routine application of molecular genetic diagnosis will probably be available in the future. Absence of epidermal basement membrane expression of alpha 5(IV) is diagnostic of XLAS, so in some cases kidney biopsy may not be necessary for diagnosis. Analysis of renal expression of alpha 3(IV)-alpha 5(IV) chains may be a useful adjunct to routine renal biopsy studies, especially when ultrastructural changes in the GBM are ambiguous. There are no specific therapies for AS. Spontaneous and engineered animal models are being used to study genetic and pharmacologic therapies. Renal transplantation for AS is usually very successful. Occasional patients develop anti-GBM nephritis of the allograft, almost always resulting in graft loss.

Laryngeal basement membrane thickening is not a reliable postmortem marker for SIDS: results from the Chicago Infant Mortality Study

It has been suggested that laryngeal basement membrane (LBM) thickening is a pathognomonic postmortem marker for sudden infant death syndrome (SIDS) and is not seen in other causes of explained sudden infant death. To test this hypothesis, we evaluated longitudinal sections of the right hemilarynx taken through the midpoint of the true vocal cord from 129 SIDS cases and 77 postneonatal sudden infant death controls. Using a five-point semi-quantitative scale, maximum LBM thickness (LBMT) for SIDS cases and controls was not statistically different (mean, 2.39 + 0.69 and 2.40 + 0.77, respectively). Likewise, scores based on the average thickness along the entire basement membrane (i.e., "average" score), were not found to be different between SIDS cases and controls. Average and maximum LBMT increased with age in both SIDS cases and controls and were not different between SIDS cases and controls within each age interval. Similar trends in the distribution of maximum and average LBMTs were found between black and Hispanic SIDS and controls; the number of white/non-Hispanic infants was too low for meaningful comparisons. Maximum and average LBMTs were not different in SIDS cases and controls exposed to environmental tobacco compared with unexposed infants. The LBMTs also increased significantly with body weight and length in both SIDS cases and controls. Finally, there were no differences in LBMT in infants intubated prior to death compared with those who were not intubated. From these data, we conclude that LBMT is not pathognomonic of SIDS, is present or absent with equal frequency in SIDS and controls, increases with postnatal age, and does not correlate with passive smoke exposure. Therefore, LBMT should not be used to diagnose SIDS.

Glomerular membranopathy in children with IgA nephropathy and Henoch Schönlein purpura

We evaluated renal biopsies from 34 children with IgA nephropathy or Henoch Schönlein purpura to further characterize the ultrastructural features of the glomerular membranopathy that occurs in these disorders. Focal glomerular basement membrane damage was identified in 29 children and was severe in 4 of the children. Alterations included focal and segmental attenuation, splitting, duplications, and spike-like subepithelial protrusions of the lamina densa, along with saccular glomerular microaneurysms arising at the paramesangium. Those cases with extensive glomerular basement membrane lesions had either moderate or severe glomerular alterations apparent by light microscopy. Over half of the cases with glomerular membranopathy had immunohistological or ultrastructural evidence of focal peripheral glomerular capillary wall immune deposits and electron-dense deposits occurred at sites of glomerular basement membrane splitting. Despite the focal attenuation of the glomerular basement membrane, we did not identify any biopsy with findings of thin basement membrane disease. The glomerular basement membrane ultrastructural findings we describe are characteristic of IgA nephropathy and Henoch Schönlein purpura, are common in children with these disorders, and are similar to the ultrastructural alterations of the basement membrane that occur in other glomerulonephritides. These basement membrane injuries may be inflammatory cell or immune mediated but their pathogenesis requires further study.

X-linked Alport syndrome in females

Alport syndrome (AS) is in the differential diagnosis of hematuria. Variability in clinical presentation and in the ultrastructural changes of the glomerulus can make the diagnosis of AS a challenge in female patients. The purpose of this report is to present immunostaining for glomerular basement membrane (GBM) expression of alpha5(IV) as an adjunctive diagnostic method. Renal biopsy specimens from eight female patients with clinical presentation suggestive of AS were studied. The patients were between 7 and 36 years of age; six were between 12 and 15 years. Light microscopy and immunohistochemistry using a monoclonal antibody to alpha5(IV) were performed. Controls showed a continuous linear pattern along the GBM in normal kidneys and absence in renal biopsy specimens from male X-linked AS patients. To express the variability of the ultrastructural GBM changes among the patients in the series, we developed a semi-quantitative Alport Index, obtained by quantification of severity and extent of ultrastructural GBM changes. With immunohistochemistry, we showed an interrupted, discontinuous linear pattern for alpha5(IV) in glomeruli from the eight patients in the series, confirming the diagnosis of X-linked AS. The ultrastructural Alport Index varied between 6 and 47, showing the heterogeneity in the severity of the GBM changes, even among the six patients aged between 12 and 15 years. In three of the eight biopsy specimens, the predominant change was thin GBM, and the Alport Index was below 20. Immunohistochemistry for alpha5(IV) in renal biopsy specimens can identify female patients heterozygous for X-linked AS. In this series, the method led to the diagnosis of AS in female patients in whom the predominant ultrastructural change was thin basement membrane.

The nonspecificity of focal segmental glomerulosclerosis. The defining characteristics of primary focal glomerulosclerosis, mesangial proliferation, and minimal change

We performed a detailed clinical review and pathologic analysis of the kidney biopsies of 134 children with nephrotic syndrome or asymptomatic proteinuria. This analysis challenges some of our concepts about the classification of conditions associated with these disorders. The presence of focal segmental sclerotic lesions does not define a unique disorder in childhood. Some children with such lesions will have unaffected glomeruli that are ultrastructurally completely normal. These patients, predominately black adolescents, present either with nephrotic syndrome or asymptomatic proteinuria. We classify this disorder as primary focal segmental glomerulosclerosis (FSGS) and have never found it to recur after transplantation. Most other children with FSGS have 1 of 2 specific glomerulopathies. Those with minimal change have generalized fusion of podocyte foot processes. Those with mesangial proliferation have similar foot process changes combined with mesangial expansion and proliferation and, frequently, thinning of the lamina densa and tubuloreticular inclusions. The presence of segmental lesions in these glomerulopathies appears to be nothing more than a marker of severity. Children with these glomerulopathies are generally younger white children, virtually all of whom have nephrotic syndrome. These disorders have a strong propensity to recur after transplantation. The presence of mesangial labeling of IgM or C1q has no significance in any of these 3 disorders. The classification of disorders associated with nephrotic syndrome or asymptomatic proteinuria must concentrate less on the presence or absence of focal sclerosis and more on the histologic appearance of the rest of the glomeruli.

Thin basement membrane nephropathy as a cause of recurrent haematuria in childhood

A survey of 69 children presenting with recurrent or persistent haematuria and submitted to percutaneous renal biopsy at this hospital over a 17-year period, was performed to establish the incidence of thin basement membrane nephropathy (TBMN). A diagnosis of primary glomerular disease was established in 44 (IgA nephropathy in 16, Alport's syndrome in 13 and other varieties of glomerulonephritis in 15). Of the remaining 25 patients in whom light microscopical and immunochemical examination revealed no abnormalities, material for electron microscopy was available in 11. In eight of these (five of whom had a family history), TBMN was diagnosed on the basis of ultrastructural morphometric evaluation of glomerular basement membrane thickness. Assuming a similar proportion of the remaining 14 patients with renal biopsy specimens normal by light microscopy had TBMN, the probable frequency of this abnormality in the whole series would be 26%, very similar to that of IgA nephropathy. In the eight TBMN patients the mean glomerular basement membrane thickness ranged between 181 and 236 nm, whilst in 'control' biopsies from children with 'minimal change' nephrotic syndrome or IgA nephropathy, the mean thickness ranged between 242 and 333 nm.