Comparison of alpha5(IV) collagen chain expression in skin with disease severity in women with X-linked Alport syndrome

A wave of deep intronic mutations in X-linked Alport Syndrome

X-linked Alport syndrome (XLAS) is an inherited kidney disease caused exclusively by pathogenic variants in the COL4A5 gene. In 10-20% of cases, DNA sequencing of COL4A5 exons or flanking regions cannot identify molecular causes. Here, our objective was to use a transcriptomic approach to identify causative events in a group of 19 patients with XLAS without identified mutation by Alport gene panel sequencing. Bulk RNAseq and/or targeted RNAseq using a capture panel of kidney genes was performed. Alternative splicing events were compared to those of 15 controls by a developed bioinformatic score. When using targeted RNAseq, COL4A5 coverage was found to be 23-fold higher than with bulk RNASeq and revealed 30 significant alternative splicing events in 17 of the 19 patients. After computational scoring, a pathogenic transcript was found in all patients. A causative variant affecting COL4A5 splicing and absent in the general population was identified in all cases. Altogether, we developed a simple and robust method for identification of aberrant transcripts due to pathogenic deep-intronic COL4A5 variants. Thus, these variants, potentially targetable by specific antisense oligonucleotide therapies, were found in a high percentage of patients with XLAS in whom pathogenic variants were missed by conventional DNA sequencing.

The Relevance of Skin Biopsies in General Internal Medicine: Facts and Myths

INTRODUCTION

Non-dermatology medical specialties may refer patients for skin biopsies, searching for a particular diagnosis. However, the diagnostic impact of the skin biopsy is not clearly established. This article aims to assess the indications for, and evaluate the clinical relevance of, skin biopsies in non-dermatology medical specialties.

METHODS

A questionnaire was sent to 23 non-dermatology specialty departments in a university medical center, requesting a list of indications for skin biopsies, as well as to 10 staff dermatologists to collect the indications of skin biopsies requested by non-dermatology specialties. Once the indications were collected, a literature search was performed to evaluate their clinical value and relevance.

RESULTS

Eleven non-dermatology specialties provided a list of skin biopsy indications, to which staff dermatologists added seven more indications. A literature search revealed evidence-based medicine data for six diseases, that is, amyloidosis, peripheral autonomic neuropathy, Sneddon's syndrome, intravascular lymphoma, sarcoidosis, and chronic graft-versus-host disease. Results were questionable concerning infectious endocarditis, acute graft-versus-host-disease, and the lupus band test. Skin biopsy were not evidenced as useful for the diagnosis of calciphylaxis, systemic scleroderma, Behçet's disease, or hypermobile Ehlers-Danlos syndrome. For the diagnosis of Alport's syndrome, pseudoxanthoma elasticum, and vascular Ehlers-Danlos syndrome, skin biopsy is currently outperformed by genetic analyses. For diagnoses such as Henoch-Schönlein purpura and Sjögren's syndrome, skin biopsy represents an additional item among other diagnostic criteria.

CONCLUSION

The usefulness of skin biopsy as requested by non-dermatology specialties is only evidenced for amyloidosis, peripheral autonomic neuropathy, Sneddon's syndrome, intravascular lymphoma, sarcoidosis, chronic graft-versus-host-disease, Henoch-Schönlein purpura, and Sjögren's syndrome.

X-Linked Kidney Disorders in Women

A number of genes that cause inherited kidney disorders reside on the X chromosome. Given that males have only a single active X chromosome, these disorders clinically manifest primarily in men and boys. However, phenotypes in female carriers of X-linked kidney conditions are becoming more and more recognized. This article reviews the biology of X inactivation as well as the kidney phenotype in women and girls with a number of X-linked kidney disorders including Alport syndrome, Fabry disease, nephrogenic diabetes insipidus, X-linked hypophosphatemic rickets, Dent disease, and Lowe syndrome.

Population-based studies reveal an additive role of type IV collagen variants in hematuria and albuminuria

Specific variants in genes that encode the α3α4α5 chains of type IV collagen cause Alport syndrome (AS), which encompass a clinical spectrum from isolated hematuria to multisystem disease affecting sight, hearing and kidney function. The commonest form is X-linked Alport syndrome (XLAS; COL4A5) with autosomal AS (COL4A3 and COL4A4) comprising a minority of cases. While historic data estimates the frequency of AS at 1:5000-10,000, recent population-based genetic studies suggest the prevalence is considerably higher. Genome-wide association studies (GWAS) have been performed in the Icelandic (deCODE) and UK (UK Biobank) populations, demonstrating an association of type IV collagen gene variants with AS relevant kidney traits. In the Icelandic population, 1 in 600 carries a 2.5-kb COL4A3 coding deletion or a COL4A3 missense variant (rs200287952[A], Gly695Arg), both of which are strongly associated with hematuria and albuminuria (P values = 1.9 × 10^-5 to 2.5 × 10^-20). In the UK Biobank, COL4A4 rs35138315 (Ser969X; carrier frequency 0.13%) is strongly associated with both hematuria and albuminuria (P = 1.5 × 10^-73). Thus, the frequency for autosomal AS is 5-16 times higher than the historic prevalence of all forms of the disorder. Furthermore, COL4A4 rs3518315 (Ser969X) is also a reported founder mutation in families with autosomal dominant focal and segmental glomerulosclerosis and autosomal recessive forms of AS. This supports an additive mode of inheritance for specific variants, wherein a number of copies of a mutation influence disease severity in a cumulative fashion. These studies did not include the X chromosome, excluding analysis of COL4A5, which represents an area for future study.

X-Linked Alport Syndrome in Women: Genotype and Clinical Course in 24 Cases

Objectives: X-linked Alport syndrome (XLAS) females are at risk of developing proteinuria and chronic kidney damage (CKD). The aim of this study is to evaluate the genotype-phenotype correlation in this rare population.

Materials and Methods: This is a prospective, observational study of XLAS females, confirmed by a pathogenic mutation in COL4A5 and renal ultrastructural evaluation. Proteinuria, renal function and extrarenal involvement were monitored during follow-up. Patients were divided in 2 groups, according to mutations in COL4A5: missense (Group 1) and non-missense variants (Group 2).

Results: Twenty-four XLAS females, aged 10.6 ± 10.4 years at clinical onset (mean follow-up: 13.1 ± 12.6 years) were recruited between 2000 and 2017 at a single center. In group 1 there were 10 patients and in group 2, 14 (mean age at the end of follow-up: 24.9 ± 13.6 and 23.2 ± 13.8 years, respectively). One patient in Group 1 and 9 in Group 2 (p = 0.013) developed proteinuria during follow-up. Mean eGFR at last follow-up was lower in Group 2 (p = 0.027), where two patients developed CKD. No differences in hearing loss were documented among the two groups. Two patients in Group 2 carried one mutation in both COL4A5 and COL4A3 (digenic inheritance) and were proteinuric. In one family, the mother presented only hematuria while the daughter was proteinuric and presented a greater inactivation of the X chromosome carrying the wild-type allele.

Conclusions: The appearance of proteinuria and CKD is more frequent in patients with severe variants. Carrying digenic inheritance and skewed XCI seem to be additional risk factors for proteinuria in XLAS females.

A review of clinical characteristics and genetic backgrounds in Alport syndrome

Alport syndrome (AS) is a progressive hereditary renal disease that is characterized by sensorineural hearing loss and ocular abnormalities. It is divided into three modes of inheritance, namely, X-linked Alport syndrome (XLAS), autosomal recessive AS (ARAS), and autosomal dominant AS (ADAS). XLAS is caused by pathogenic variants in COL4A5, while ADAS and ARAS are caused by those in COL4A3/COL4A4. Diagnosis is conventionally made pathologically, but recent advances in comprehensive genetic analysis have enabled genetic testing to be performed for the diagnosis of AS as first-line diagnosis. Because of these advances, substantial information about the genetics of AS has been obtained and the genetic background of this disease has been revealed, including genotype-phenotype correlations and mechanisms of onset in some male XLAS cases that lead to milder phenotypes of late-onset end-stage renal disease (ESRD). There is currently no radical therapy for AS and treatment is only performed to delay progression to ESRD using nephron-protective drugs. Angiotensin-converting enzyme inhibitors can remarkably delay the development of ESRD. Recently, some new drugs for this disease have entered clinical trials or been developed in laboratories. In this article, we review the diagnostic strategy, genotype-phenotype correlation, mechanisms of onset of milder phenotypes, and treatment of AS, among others.

A review of clinical characteristics and genetic backgrounds in Alport syndrome

Alport syndrome (AS) is a progressive hereditary renal disease that is characterized by sensorineural hearing loss and ocular abnormalities. It is divided into three modes of inheritance, namely, X-linked Alport syndrome (XLAS), autosomal recessive AS (ARAS), and autosomal dominant AS (ADAS). XLAS is caused by pathogenic variants in COL4A5, while ADAS and ARAS are caused by those in COL4A3/COL4A4. Diagnosis is conventionally made pathologically, but recent advances in comprehensive genetic analysis have enabled genetic testing to be performed for the diagnosis of AS as first-line diagnosis. Because of these advances, substantial information about the genetics of AS has been obtained and the genetic background of this disease has been revealed, including genotype–phenotype correlations and mechanisms of onset in some male XLAS cases that lead to milder phenotypes of late-onset end-stage renal disease (ESRD). There is currently no radical therapy for AS and treatment is only performed to delay progression to ESRD using nephron-protective drugs. Angiotensin-converting enzyme inhibitors can remarkably delay the development of ESRD. Recently, some new drugs for this disease have entered clinical trials or been developed in laboratories. In this article, we review the diagnostic strategy, genotype–phenotype correlation, mechanisms of onset of milder phenotypes, and treatment of AS, among others.

Detection of Splicing Abnormalities and Genotype-Phenotype Correlation in X-linked Alport Syndrome

BACKGROUND

X-linked Alport syndrome (XLAS) is a progressive hereditary nephropathy caused by mutations in the COL4A5 gene. Genotype-phenotype correlation in male XLAS is relatively well established; relative to truncating mutations, nontruncating mutations exhibit milder phenotypes. However, transcript comparison between XLAS cases with splicing abnormalities that result in a premature stop codon and those with nontruncating splicing abnormalities has not been reported, mainly because transcript analysis is not routinely conducted in patients with XLAS.

METHODS

We examined transcript expression for all patients with suspected splicing abnormalities who were treated at one hospital between January of 2006 and July of 2017. Additionally, we recruited 46 males from 29 families with splicing abnormalities to examine genotype-phenotype correlation in patients with truncating (n=21, from 14 families) and nontruncating (n=25, from 15 families) mutations at the transcript level.

RESULTS

We detected 41 XLAS families with abnormal splicing patterns and described novel XLAS atypical splicing patterns (n=14) other than exon skipping caused by point mutations in the splice consensus sequence. The median age for developing ESRD was 20 years (95% confidence interval, 14 to 23 years) among patients with truncating mutations and 29 years (95% confidence interval, 25 to 40 years) among patients with nontruncating mutations (P=0.001).

CONCLUSIONS

We report unpredictable atypical splicing in the COL4A5 gene in male patients with XLAS and reveal that renal prognosis differs significantly for patients with truncating versus nontruncating splicing abnormalities. Our results suggest that splicing modulation should be explored as a therapy for XLAS with truncating mutations.

A Novel Mutation in a Japanese Family with X-linked Alport Syndrome

We herein report a novel mutation in a Japanese family with an X-linked Alport syndrome (AS) mutation in COL4A5. Patient 1 was a 2-year-old Japanese girl. She and her mother (patient 2) had a history of proteinuria and hematuria without renal dysfunction, deafness, or ocular abnormalities. Pathological findings were consistent with AS, and a genetic analysis revealed that both patients had a heterozygous mutation (c.2767G>C) in exon 32. In summary, the identification of mutations and characteristic pathological findings was useful in making a diagnosis of AS. For a close long-term follow-up, the early detection and treatment of women with X-linked AS are important.

X-linked Alport syndrome associated with a synonymous p.Gly292Gly mutation alters the splicing donor site of the type IV collagen alpha chain 5 gene

BACKGROUND

X-linked Alport syndrome (XLAS) is a progressive hereditary nephropathy caused by mutations in the type IV collagen alpha chain 5 gene (COL4A5). Although many COL4A5 mutations have previously been identified, pathogenic synonymous mutations have not yet been described.

METHODS

A family with XLAS underwent mutational analyses of COL4A5 by PCR and direct sequencing, as well as transcript analysis of potential splice site mutations. In silico analysis was also conducted to predict the disruption of splicing factor binding sites. Immunohistochemistry (IHC) of kidney biopsies was used to detect α2 and α5 chain expression.

RESULTS

We identified a hemizygous point mutation, c.876A>T, in exon 15 of COL4A5 in the proband and his brother, which is predicted to result in a synonymous amino acid change, p.(Gly292Gly). Transcript analysis showed that this mutation potentially altered splicing because it disrupted the splicing factor binding site. The kidney biopsy of the proband showed lamellation of the glomerular basement membrane (GBM), while IHC revealed negative α5(IV) staining in the GBM and Bowman's capsule, which is typical of XLAS.

CONCLUSIONS

This is the first report of a synonymous COL4A5 substitution being responsible for XLAS. Our findings suggest that transcript analysis should be conducted for the future correct assessment of silent mutations.

X-linked Alport syndrome caused by splicing mutations in COL4A5

BACKGROUND AND OBJECTIVES

X-linked Alport syndrome is caused by mutations in the COL4A5 gene. Although many COL4A5 mutations have been detected, the mutation detection rate has been unsatisfactory. Some men with X-linked Alport syndrome show a relatively mild phenotype, but molecular basis investigations have rarely been conducted to clarify the underlying mechanism.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In total, 152 patients with X-linked Alport syndrome who were suspected of having Alport syndrome through clinical and pathologic investigations and referred to the hospital for mutational analysis between January of 2006 and January of 2013 were genetically diagnosed. Among those patients, 22 patients had suspected splice site mutations. Transcripts are routinely examined when suspected splice site mutations for abnormal transcripts are detected; 11 of them showed expected exon skipping, but others showed aberrant splicing patterns. The mutation detection strategy had two steps: (1) genomic DNA analysis using PCR and direct sequencing and (2) mRNA analysis using RT-PCR to detect RNA processing abnormalities.

RESULTS

Six splicing consensus site mutations resulting in aberrant splicing patterns, one exonic mutation leading to exon skipping, and four deep intronic mutations producing cryptic splice site activation were identified. Interestingly, one case produced a cryptic splice site with a single nucleotide substitution in the deep intron that led to intronic exonization containing a stop codon; however, the patient showed a clearly milder phenotype for X-linked Alport syndrome in men with a truncating mutation. mRNA extracted from the kidney showed both normal and abnormal transcripts, with the normal transcript resulting in the milder phenotype. This novel mechanism leads to mild clinical characteristics.

CONCLUSIONS

This report highlights the importance of analyzing transcripts to enhance the mutation detection rate and provides insight into genotype-phenotype correlations. This approach can clarify the cause of atypically mild phenotypes in X-linked Alport syndrome.

Milder clinical aspects of X-linked Alport syndrome in men positive for the collagen IV α5 chain

X-linked Alport syndrome is caused by mutations in the COL4A5 gene encoding the type IV collagen α5 chain (α5(IV)). Complete absence of α5(IV) in the renal basal membrane is considered a pathological characteristic in male patients; however, positive α5(IV) staining has been found in over 20% of patients. We retrospectively studied 52 genetically diagnosed male X-linked Alport syndrome patients to evaluate differences in clinical characteristics and renal outcomes between 15 α5(IV)-positive and 37 α5(IV)-negative patients. Thirteen patients in the α5(IV)-positive group had non-truncating mutations consisting of nine missense mutations, three in-frame deletions, and one splice-site mutation resulting in small in-frame deletions of transcripts. The remaining two showed somatic mutations with mosaicism. Missense mutations in the α5(IV)-positive group were more likely to be located before exon 25 compared with missense mutations in the α5(IV)-negative group. Furthermore, urinary protein levels were significantly lower and the age at onset of end-stage renal disease was significantly higher in the positive group than in the negative group. These results help to clarify the milder clinical manifestations and molecular characteristics of male X-linked Alport syndrome patients expressing the α5(IV) chain.

The variable course of women with X-linked Alport Syndrome

X-linked Alport syndrome (XLAS) arises from mutations in the COL4A5 gene encoding the α5-chain of type IV collagen and is associated with hematuria, ocular abnormalities and high-tone sensorineural hearing loss. Nearly all affected males have decreased kidney function resulting in end-stage renal disease (ESRD) as early as the second decade of life. It was long thought that affected females had a benign outcome; however, in recent decades, it has become quite clear that they too are at risk for developing nephrotic syndrome, decreased kidney function and ESRD. We report two young females presenting with microscopic hematuria and proteinuria diagnosed with XLAS on renal biopsy. Both developed nephrotic-range proteinuria and progressive renal insufficiency. Additionally, both developed extra-renal manifestations of XLAS. The ultrastructural and immunofluorescence features on kidney biopsy were instrumental in making the diagnosis of heterozygous XLAS as neither patient had a family history of AS.

Expert guidelines for the management of Alport syndrome and thin basement membrane nephropathy

Few prospective, randomized controlled clinical trials address the diagnosis and management of patients with Alport syndrome or thin basement membrane nephropathy. Adult and pediatric nephrologists and geneticists from four continents whose clinical practice focuses on these conditions have developed the following guidelines. The 18 recommendations are based on Level D (Expert opinion without explicit critical appraisal, or based on physiology, bench research, or first principles-National Health Service category) or Level III (Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees-U.S. Preventive Services Task Force) evidence. The recommendations include the use of genetic testing as the gold standard for the diagnosis of Alport syndrome and the demonstration of its mode of inheritance; the need to identify and follow all affected members of a family with X-linked Alport syndrome, including most mothers of affected males; the treatment of males with X-linked Alport syndrome and individuals with autosomal recessive disease with renin-angiotensin system blockade, possibly even before the onset of proteinuria; discouraging the affected mothers of males with X-linked Alport syndrome from renal donation because of their own risk of kidney failure; and consideration of genetic testing to exclude X-linked Alport syndrome in some individuals with thin basement membrane nephropathy. The authors recognize that as evidence emerges, including data from patient registries, these guidelines will evolve further.

Women and Alport syndrome

X-linked Alport syndrome (XLAS) is caused by mutations in type IV collagen causing sensorineural hearing loss, eye abnormalities, and progressive kidney dysfunction that results in near universal end-stage renal disease (ESRD) and the need for kidney transplantation in affected males. Until recent decades, the disease burden in heterozygous "carrier" females was largely minimized or ignored. Heterozygous females have widely variable disease outcomes, with some affected females exhibiting normal urinalysis and kidney function, while others develop ESRD and deafness. While the determinants of disease severity in females with XLAS are uncertain, skewing of X-chromosome inactivation has recently been found to play a role. This review will explore the natural history of heterozygous XLAS females, the determinants of disease severity, and the utility of using XLAS females as kidney donors.

Severe Alport syndrome in a young woman caused by a t(X;1)(q22.3;p36.32) balanced translocation

The course of renal involvement and hearing loss is much milder in most female X-linked Alport syndromes than in male patients. We examined the molecular mechanism of development of the disease in a female patient with severe Alport syndrome. The patient showed heavy proteinuria, hematuria, neurosensory hearing loss and primary amenorrhea. Renal biopsy findings of electron microscopy and immunostaining of the alpha5 chain of type IV collagen indicated a female X-linked Alport syndrome. G-banding chromosomal analysis showed a t(X;1)(q22.3;p36.32) balanced translocation. Analysis of the collagen type IV (COL4A5) gene by genomic DNA sequencing, complementary DNA (cDNA) sequencing and multiplex ligation-dependent probe amplification assay showed no mutations or deletions/duplications of the gene. However, fluorescence in situ hybridization using the probes for exon 1 and exon 51 of the COL4A5 gene showed disruption of one copy of the gene. Replication R-banding chromosomal analysis indicated preferential inactivation of the normal X chromosome. This is the first report of severe Alport syndrome in a female patient carrying a balanced translocation between the chromosome X and 1 producing the disruption of one copy of COL4A5 gene and silencing of the other copy because of preferential inactivation of the normal X chromosome. Chromosomal abnormalities should be considered in female patients with severe forms of Alport syndrome.

X-inactivation modifies disease severity in female carriers of murine X-linked Alport syndrome

BACKGROUND

Female carriers of X-linked Alport syndrome (XLAS) demonstrate variability in clinical phenotype that, unlike males, cannot be correlated with genotype. X-inactivation, the method by which females (XX) silence transcription from one X chromosome in order to achieve gene dosage parity with males (XY), likely modifies the carrier phenotype, but this hypothesis has not been tested directly.

METHODS

Using a genetically defined mouse model of XLAS, we generated two groups of Alport female (Col4a5(+/-)) carriers that differed only in the X-controlling element (Xce) allele regulating X-inactivation. We followed the groups as far as 6 months of age comparing survival and surrogate outcome measures of urine protein and plasma urea nitrogen.

RESULTS

Preferential inactivation of the mutant Col4a5 gene improved survival and surrogate outcome measures of urine protein and plasma urea nitrogen. In studies of surviving mice, we found that X-inactivation in kidney, measured by allele-specific mRNA expression assays, correlated with surrogate outcomes.

CONCLUSIONS

Our findings establish X-inactivation as a major modifier of the carrier phenotype in X-linked Alport syndrome. Thus, X-inactivation patterns may offer prognostic information and point to possible treatment strategies for symptomatic carriers.

Novel corneal phenotype in a patient with alport syndrome

PURPOSE

To report the clinical and histopathologic findings of an unusual keratopathy, which may represent a new corneal dystrophy in a patient with Alport syndrome (ATS).

METHODS

A 59-year-old woman with longstanding diagnosis of autosomal recessive ATS was evaluated for progressively decreasing vision in the left eye. She had anterior lenticonus and cataract and central corneal stromal opacification with significant thinning and flattening bilaterally. She underwent penetrating keratoplasty and cataract extraction with posterior chamber intraocular lens implantation. We describe the light microscopic and ultrastructural findings from the cornea.

RESULTS

Histopathology of the corneal button revealed marked stromal thinning with decreased keratocytes. The endothelial cells were attenuated and focally lost. Immunohistochemical stains for cytokeratin were positive, findings consistent with posterior polymorphous dystrophy (PPMD). Transmission electron microscopy showed necrosis and a marked loss of keratocytes. Multilayering of the endothelium was consistent with PPMD, but mature desmosomes and microvilli were absent. In vivo confocal microscopy on the fellow eye showed linear hyporeflective bands at the level of Descemet's membrane consistent with PPMD. In addition, there were fine linear changes in the deep stroma and diffuse hyperreflectivity of the mid and superficial stroma with lack of identifiable keratocytes throughout.

CONCLUSIONS

We believe this to be the first reported case to demonstrate some histopathologic features of PPMD in ATS. However, the clinical, histopathologic, and ultrastructural characteristics are not typical of PPMD. This may represent a new phenotypic expression of PPMD or may be a distinct clinicopathologic dystrophy associated with ATS.

Somatic mosaicism for a mutation of the COL4A5 gene is a cause of mild phenotype male Alport syndrome

BACKGROUND

Alport syndrome is the most common form of hereditary nephritis and is mainly caused by mutations in the COL4A5 gene, which shows the X-linked form. It is well known that some male Alport syndrome cases show a relatively mild phenotype, but few molecular investigations have been conducted to clarify the mechanism of this phenotype. Methods and results. This report concerns an 8-year-old male sporadic Alport syndrome patient. While electron microscopy of the glomerular basement membrane showed typical findings for Alport syndrome, however, the immunohistochemical analysis of the glomerulus showed mosaic staining of the type IV collagen alpha 5 chain. The mutational analysis of the COL4A5 gene unexpectedly disclosed two peaks at the intron 43 splicing acceptor site (c. 3998-2 a/t) with direct sequencing. Restriction enzyme analysis demonstrated that the presence of somatic mosaicism was responsible for this mutation. mRNA extracted from the urinary sediments was analysed by RT-PCR and two PCR fragments were amplified, one consisting of a normal sequence and one with skipping of exon 44.

CONCLUSIONS

Our findings indicate that somatic mosaicism for COL4A5 is responsible for male X-linked Alport syndrome with an alpha 5 mosaic staining pattern. Several cases with somatic mosaicism have previously been reported, however, this is the first case where the presence of this mutation was proved with a comprehensive analysis of genomic DNA, mRNA and alpha 5 expression in the tissues. Somatic mosaicism may thus be one of the causes of the mild phenotype in Alport syndrome.

Collagen α5 and α2(IV) chain coexpression: Analysis of skin biopsies of Alport patients

Alport syndrome is a collagen type IV disease caused by mutations in the COL4A5 gene with the X-linked form being most prevalent. The resultant alpha5(IV) collagen chain is a component of the glomerular and skin basement membranes (SBMs). Immunofluorescent determination of the alpha5(IV) chain in skin biopsies is the procedure of choice to identify patients. In 30% of patients, however, the mutant protein is still found in the SBM resulting in a normal staining pattern. In order to minimize or eliminate false results, we compared the distribution of the alpha2(IV) chain (another SBM component) and the alpha5(IV) chain by standard double label immunofluorescence (IF) and by confocal laser scanning microscopy. The study was performed on 55 skin biopsies of patients suspected of Alports and five normal control specimens. In normal skin, IF showed the classical linear pattern for both collagens along the basement membrane. Additionally, decreased alpha5(IV) was found in the bottom of the dermal papillary basement membrane. Confocal analysis confirmed the results and show alpha5(IV) focal interruptions. In suspected patients, both techniques showed the same rate of abnormal alpha5(IV) expression: segmental in women and absent in men. Our results show a physiological variation of alpha5(IV) location with focal interruptions and decreased expression in the bottom of the dermal basement membrane. Comparison of alpha5(IV) with alpha2(IV) expression is simple and eliminates technical artifacts.

Discordance between skin biopsy and kidney biopsy in an X-linked carrier of Alport syndrome

Alport syndrome (AS) is the most common form of hereditary nephritis. Females with X-linked AS are heterozygous carriers of the disease mutation. Carrier status in females without a family history has traditionally been diagnosed by kidney biopsy; more recently skin biopsy has been utilized. We report on a 14-year-old girl with long-standing hematuria and intermittent proteinuria who underwent kidney and skin biopsy to establish a definitive diagnosis. Electron microscopy showed extensive thinning of glomerular basement membrane (GBM), with no evidence of lamination. Immunofluorescence staining showed continuous GBM staining for the alpha3(IV) and alpha5(IV) collagen chains, whereas the epidermal basement membrane showed discontinuous alpha5(IV) collagen staining consistent with an X-linked carrier of AS. Few reports have shown discordance between kidney and skin biopsy findings as seen in this case, presumably due to X chromosome lyonization. We therefore suggest that simultaneous kidney and skin biopsies may be more accurate in the assessment of potential female carriers of AS than either kidney biopsy or skin biopsy alone.

Segmental Membranous Glomerulonephritis in Children: Comparison with Global Membranous Glomerulonephritis

Generally, idiopathic membranous glomerulonephritis (MGN) is a global glomerular disease that affects the whole of the glomerulus. However, idiopathic segmental MGN (SMGN) that shows IgG deposits in a portion of the glomerulus is encountered often. For clarification of whether SMGN is the same entity as idiopathic global MGN (GMGN), the two diseases were compared. From 1978 to 2004, 38 children (11 with SMGN and 27 with GMGN) received a diagnosis of idiopathic MGN. Immunofluorescence microscopy showed segmental granular IgG staining along the capillary loops in SMGN, whereas GMGN showed global staining. On light microscopy, SMGN showed segmental thickening of the glomerular basement membrane, with spike formation, whereas GMGN showed global lesions. The frequency of C1q deposits in SMGN was significantly higher than that in GMGN (91 versus 41%; P < 0.01). On electron microscopy, mesangial electron-dense deposits were detected in 10 (91%) cases of SMGN and also were found in the subepithelial and intramembranous area, whereas only six (22%) cases of GMGN had mesangial electron-dense deposits (P < 0.001). There were no significant differences in clinical features between the groups. Two children with SMGN underwent a repeat biopsy 3 yr after the first biopsy, and both patients again showed SMGN. At the final observation (mean observation time 7.5 yr in SMGN and 12.4 yr in GMGN), all children of both groups had a good outcome. In conclusion, these findings as a whole suggest that SMGN may be another glomerular disease entity with child predominance that is distinctive from GMGN.

Tissue-specific distribution of an alternatively spliced COL4A5 isoform and non-random X chromosome inactivation reflect phenotypic variation in heterozygous X-linked Alport syndrome

A novel type of hereditary transmission of COL4A5 in a Japanese family with X-linked Alport syndrome was detected through analysis of cDNA sequences and an X-chromosome inactivation assay. A female patient with moderately altered renal function, who was diagnosed with Alport syndrome by renal biopsy, and her mother, who was undergoing maintenance haemodialysis, showed similar tissue-specific expression of a truncated isoform of COL4A5, which was generated by alternative splicing without a splice-site mutation. Expression of the truncated isoform occurred in the renal specimen derived from the patient, but not in specimens from controls. Genomic analysis revealed two point mutations (c.4821 + 121, T>C; c.4822-151_150, ins T) in intron 49 of COL4A5 from the patient. The peripheral blood mononuclear cells of the patient and her mother showed non-random lyonization. While the females showed only renal impairment, an affected male in the same family suffered from severe renal insufficiency, visual defect and hearing disturbances. Hence, we suggest that this type of heredity COL4A5 presents with phenotypic variation in female heterozygous X-linked Alport syndrome patients.

X-linked Alport syndrome: natural history and genotype-phenotype correlations in girls and women belonging to 195 families: a "European Community Alport Syndrome Concerted Action" study

Alport syndrome (AS) is a type IV collagen hereditary disease characterized by progressive hematuric nephritis, hearing loss, and ocular changes. Mutations in the COL4A5 collagen gene are responsible for the more common X-linked dominant form of the disease characterized by much less severe disease in girls and women. A "European Community Alport Syndrome Concerted Action" (ECASCA) group was established to delineate the Alport syndrome phenotype in each gender and to determine genotype-phenotype correlations in a large number of families. Data concerning 329 families, 250 of them with an X-linked transmission, were collected. Characteristics of heterozygous girls and women belonging to the 195 families with proven COL4A5 mutation are compared with those of hemizygous boys and men. Hematuria was observed in 95% of carriers and consistently absent in the others. Proteinuria, hearing loss, and ocular defects developed in 75%, 28%, and 15%, respectively. The probability of developing end-stage renal disease or deafness before the age of 40 yr was 12% and 10%, respectively, in girls and women versus 90 and 80%, respectively, in boys and men. The risk of progression to end-stage renal disease appears to increase after the age of 60 yr in women. Because of the absence of genotype-phenotype correlation and the large intrafamilial phenotypic heterogeneity, early prognosis of the disease in X-linked Alport syndrome carriers remains moot. Risk factors for developing renal failure have been identified: the occurrence and progressive increase in proteinuria, and the development of a hearing defect.

Epidermal basement membrane alpha 5(IV) expression in females with Alport syndrome and severity of renal disease

BACKGROUND

X-linked Alport syndrome is a progressive nephritis caused by mutations of the COL4A5 gene. This gene encodes the collagen alpha 5(IV) chain, which is abnormally distributed in the glomerular basement membrane (GBM) and epidermal basement membrane (EBM). It has been reported a negative correlation between alpha 5(IV) chain distribution in EBM and the degree of proteinuria in heterozygous females with Alport syndrome.

METHODS

In the present study, we evaluated the distribution of the alpha 5(IV) chain in the EBM and the degree of proteinuria in 22 females with X-linked Alport syndrome. The distribution of the cutaneous alpha 5(IV) chain was measured by a confocal laser microscope using an anti-alpha 5(IV) monoclonal antibody. The expression ratio of alpha 5(IV) distribution was quantified dividing the extension of the positive signal and the maximal extension of the specimen. Urinary protein excretion was expressed as urinary protein over urinary creatinine ratio.

RESULTS

Proteinuria was present in five of the 22 patients. In two patients with proteinuria, alpha 5(IV)chain was normally distributed; in the remaining three, the expression ratio of alpha 5(IV)chain was 35%, 47%, and 48%. Of the 17 patients without proteinuria, two displayed a complete absence of the alpha 5(IV) chain in EBM, five displayed a normal staining, and the remaining 10 had an expression ratio between 18% and 65%.

CONCLUSION

Our data suggest that there is no correlation between the severity of the glomerular involvement (expressed by proteinuria) and the staining of the alpha 5 chain in the EBM in females with X-linked Alport syndrome.

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.

Contemporary diagnostic approach in Alport's syndrome

Diagnosis of Alport's syndrome rests on clinical, pathological and genetic criteria. The clinical criteria include positive family history, persistent microhematuria and extrarenal abnormalities involving eyes and ears. Besides kidney biopsy, skin biopsy has emerged recently as an interesting diagnostic tool: the absence of staining for the alpha5 chain of type IV collagen in the epidermal basement membrane is highly specific of x-linked Alport's syndrome but its sensitivity is approximately 75%. Genetic diagnosis is based on direct identification of the mutation involved (positive in 50% of the families, after long and tedious search) or on linkage analysis. An integrated approach to diagnosis of Alport's syndrome (which encompasses various diseases characterized by different molecular defects) has been greatly facilitated in the last 10 years.

Identification of COL4A5 defects in Alport's syndrome by immunohistochemistry of skin

BACKGROUND

The COL4A3-COL4A4-COL4A5 network in the glomerular basement membrane is affected in the inherited renal disorder Alport's syndrome (AS). Approximately 85% of the AS patients are expected to carry a mutation in the X-chromosomal COL4A5 gene and 15% in the autosomal COL4A3 and COL4A4 genes. The COL4A5 chain is also present in the epidermal basement membrane (EBM). It is predicted that approximately 70% of the COL4A5 mutations prevent incorporation of this chain in basement membranes.

METHODS

We investigated whether or not COL4A5 defects could be detected by immunohistochemical analysis of the EBM. Punch skin biopsies were obtained from 22 patients out of 17 families and two biopsy specimens from healthy males were used as controls.

RESULTS

In four cases with the COL4A5 frameshift or missense mutations, the COL4A5 chain was either lacking from the EBM (male) or showed a focally negative pattern (female). In three other patients with a COL4A5 missense mutation, a COL4A3 and a COL4A4 mutation, respectively, the COL4A5 staining was normal. A (focally) negative EBM-COL4A5 staining was found in three patients of six families with a diagnosis of AS and in one family of a group of four families with possible AS.

CONCLUSIONS

The (focal) absence of COL4A5 in the EBM of skin biopsy specimens can be used for fast identification of COL4A5 defects. Combined with polymorphic COL4A5 markers, both postnatal and prenatal DNA diagnosis are possible in the family of the patient.