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 α3(IV) and α5(IV) collagen chains, whereas the epidermal basement membrane showed discontinuous α5(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.     

A novel G472R mutation in a Turkish family with X-linked Alport syndrome

Alport syndrome (AS) is a hereditary disorder of progressive nephritis. Most cases are X-linked, but autosomal forms have been reported. The X-linked form is associated with mutations in the COL4A5 gene that encodes the α5 chain of type IV collagen. More than 200 mutations have been reported in X-linked AS. We report a novel 1616 G>A mutation resulting in glycine substitution to arginine at position 472 in a Turkish family with a severely affected man and several variably affected women. This is the first Turkish family in whom the molecular basis of the disease has been reported. Received: 16 December 1998 / Revised: 30 June 1999 / Accepted: 7 July 1999     

Female X-linked Alport syndrome with somatic mosaicism

Background

X-linked Alport syndrome (XLAS) is a progressive, hereditary nephropathy. Although males with XLAS usually develop end-stage renal disease before 30 years of age, some men show a milder phenotype and possess somatic mosaic variants of the type IV collagen α5 gene (COL4A5), with severity depending on variant frequencies. In females, somatic mosaic variants are rarely reported in XLAS, and it is not clear what determines severity.

Methods

Two females with somatic mosaic mutations in COL4A5 with variant frequencies of 17.9 and 22.1% were detected using the next-generation sequencing. One patient only had hematuria. The other, however, had moderate proteinuria, which is a severe phenotype for a female XLAS patient of her age. The molecular mechanisms for the severe phenotype were investigated by examining variant frequencies in urinary sediment cells and X chromosome inactivation patterns, and by looking for modifier variants in podocyte-related genes using the next-generation sequencing.

Results

The severe phenotype patient had a variant frequency of 36.6% in urinary sediment cells, which is not markedly high, nor did she show skewed X chromosome inactivation. However, she did have the heterozygous variant in COL4A3, which can affect severity.

Conclusion

Factors determining severity in female XLAS patients remain unclear. One studied patient with the somatic variant in COL4A5 showed a severe phenotype without skewed X chromosome inactivation, which might be derived from digenic variants in COL4A3 and COL4A5. Further studies are required to determine molecular mechanisms behind female XLAS resulting in the severe phenotype.

     

Mouse model of X-linked Alport syndrome

X-linked Alport syndrome (XLAS) is a progressive disorder of basement membranes caused by mutations in the COL4A5 gene, encoding the alpha5 chain of type IV collagen. A mouse model of this disorder was generated by targeting a human nonsense mutation, G5X, to the mouse Col4a5 gene. As predicted for a nonsense mutation, hemizygous mutant male mice are null and heterozygous carrier female mice are mosaic for alpha5(IV) chain expression. Mutant male mice and carrier female mice are viable through reproductive age and fertile. Mutant male mice died spontaneously at 6 to 34 wk of age, and carrier female mice died at 8 to 45 wk of age, manifesting proteinuria, azotemia, and progressive and manifold histologic abnormalities of the kidney glomerulus and tubulointerstitium. Ultrastructural abnormalities of the glomerular basement membrane, including lamellation and splitting, were characteristic of human XLAS. The mouse model described here recapitulates essential clinical and pathologic findings of human XLAS. With alpha5(IV) expression reflecting X-inactivation patterns, it will be especially useful in studying determinants of disease variability in the carrier state.     

A new point mutation in the COL4A5 gene described in a Spanish family with X-linked Alport syndrome

BACKGROUND/AIM: Alport syndrome is a hereditary glomerulonephritis, X-linked in 85% of the cases. This form is associated with mutations in the COL4A5 gene which encodes the alpha5 chain of type IV collagen. We have performed the mutational analysis of the COL4A5 gene in a Spanish family with X-linked Alport syndrome. METHODS: We have analyzed three polymorphic markers close to the gene to confirm the X chromosome linkage. By means of the PCR technique, we have screened the 51 exons of the gene. RESULTS: The segregation of the alleles from the analyzed markers was in agreement with the X linkage. Direct sequencing of PCR-amplified products has shown a CCT-to-CTT change in exon 25, resulting in substitution of a proline for a leucine at position 619 of the polypeptide chain (nucleotide 2058). CONCLUSIONS: Although proline is considered a nonconserved amino acid, it is essential, upon hydroxylation, in the maintenance of a stable alpha chain triple-helix collagen. Furthermore, the change cosegregates with the disease in all affected members of the family, not being present in 80 control chromosomes. This represents a new mutation in the COL4A5 gene found in the Spanish population.     

A female with X-linked Alport syndrome and compound heterozygous COL4A5 mutations

Background

Female subjects with X-linked Alport syndrome have a single COL4A5 mutation, germ cell mosaicism in affected tissues and typically develop renal failure later or less often than male subjects. Women with two mutations are exceedingly rare, and usually have consanguineous parents or uniparental disomy. We describe here a 20-year-old woman who inherited two different COL4A5 variants, one from her father (c.2677G>C) and one from her mother (c.384 +1 G>A).

Case-diagnosis/treatment

The index case had normal renal function, proteinuria and no clinically detectable hearing loss, or ocular abnormalities. Her father and paternal uncle developed end-stage renal disease at 37 and 28 years respectively, together with hearing loss, but not lenticonus or central retinopathy. Her mother had mildly impaired renal function, proteinuria, hearing loss, but no ocular abnormalities. Her maternal grandfather and 22-year-old brother, both with this mutation, developed renal failure by 28 years with hearing loss, or had proteinuria and hearing loss respectively.

Conclusion

The index case has clinical features consistent with germ cell mosaicism of two COL45A mutations associated with adult-onset renal failure, but no ocular abnormalities. Her risk of renal failure is high, but the rate of progression to end-stage disease depends on the underlying mutations, and disease modification with renin–angiotensin blockade.     

Resolution of proteinuria in a patient with X-linked Alport syndrome treated with cyclosporine

We report a 9-year-old Icelandic male with Alport syndrome and nephrotic-range proteinuria who responded well to cyclosporine therapy. He presented at the age of 2 years with gross hematuria and proteinuria during an episode of upper respiratory tract infection. Three years later he had developed persistent proteinuria; kidney function was normal. A renal biopsy revealed marked irregularities in the glomerular basement membrane consistent with Alport syndrome. Mutation analysis revealed a single base insertion in COL4A5 which was predicted to cause a major structural defect in the collagen IV alpha5 chain. Despite angiotensin-converting enzyme inhibitor therapy his proteinuria progressed to the nephrotic range associated with edema. At the age of 7 years, cyclosporine therapy was instituted, which promptly resulted in almost complete resolution of proteinuria. Three years later his urinary protein excretion was close to the normal range and serum creatinine remained within normal limits. We conclude that closely monitored cyclosporine therapy may be a safe and effective treatment in patients with severe proteinuria and Alport syndrome.     

Absence of α6(IV) collagen in kidney and skin of X-linked Alport syndrome patients

Ab stract. To identify the abnormalities of the type IV collagen α6 chain, α6(IV), in Alport syndrome, we examined renal and skin tissue using rat monoclonal antibodies against non-consensus amino acid sequences of α6(IV). Immunofluorescence of normal human kidney and skin tissue revealed linear α6(IV) staining in the basement membrane (BM) of Bowman’s capsule, in some tubules, and also in the epidermal BM. Renal specimens from five male patients of four families with X-linked Alport syndrome showed no reactivity for α6(IV) in Bowman’s capsules and tubules. In these patients, α1(IV) and α2(IV) were normal, whereas α3(IV), α4(IV), and α5(IV) were absent from the BMs of the kidney. In skin tissue of male patients, neither α5(IV) nor α6(IV) were detected. The epidermal BM of female heterozygotes with X-linked Alport syndrome showed a mosaic staining for α5(IV) and α6(IV). These findings indicate that, in addition to a disturbed α3(IV)-α4(IV)-α5(IV) network, patients with X-linked Alport syndrome have abnormalities in α6(IV) of the renal and epidermal BMs at the protein level. Received October 6, 1995; received in revised form April 25, 1996; accepted April 29, 1996     

Characterization of the peripheral retinopathy in X-linked and autosomal recessive Alport syndrome.

BACKGROUND: Alport syndrome is an inherited disease resulting in kidney failure, hearing loss and ocular abnormalities. Alport syndrome is however often unrecognized, and the aim of this study was to characterize the associated but rarely described peripheral retinopathy and determine whether its demonstration was diagnostically helpful. METHODS: Index cases were diagnosed with Alport syndrome on renal biopsy in themselves or a family member. Inheritance and affected status were determined using microsatellite markers at the COL4A5 and COL4A3/COL4A4 loci, respectively. Participants' eyes were dilated, and examined with direct and indirect ophthalmoscopy, and slit lamp biomicroscopy by an expert ophthalmologist who was unaware of the patients' disease status. RESULTS: Ten males and nine females with X-linked Alport syndrome and seven with autosomal recessive disease were studied. Of the 26 patients, 16 had central retinopathy (62%), and 19 patients had peripheral retinopathy (74%). The peripheral changes occurred in both males and females with X-linked and autosomal recessive Alport syndrome, and were more common when renal failure, hearing loss, lenticonus and the central changes were present, but were also noted in 3 X-linked carriers with normal renal function. CONCLUSIONS: The peripheral retinopathy occurs in X-linked and autosomal recessive Alport syndrome even when the central retinopathy is absent. Careful retinal examination and photography that includes the periphery is a safe and inexpensive method that may help in the diagnosis of Alport syndrome especially in carriers of X-linked disease.     

一个Alport综合征家系的基因连锁分析

目的用基因连锁分析方法对一个Ａｌｐｏｒｔ综合征家系的致病基因定位。方法应用聚合酶链反应（ＰＣＲ）方法分别扩增与２号染色体上Ⅳ型胶原α３和α４链基因（ＣＯＬ４Ａ３／ＣＯＬ４Ａ４）连锁的微卫星遗传标记ＣＡ１１、ＰＡＸ３、Ｄ２Ｓ４０１及与Ｘ染色体上Ⅳ型胶原α５链基因（ＣＯＬ４Ａ５）紧密连锁的微卫生遗传标记２Ｂ６、ＤＸＳ１０１,找出家系中与疾病连锁的单体型,并计算出Ｌｏｄ Ｓｃｏｒｅ值,从而判定是否存在连     

Meta-analysis of genotype-phenotype correlation in X-linked Alport syndrome: impact on clinical counselling.

BACKGROUND: Alport syndrome (AS) is a hereditary nephropathy characterized by progressive renal failure, hearing loss and ocular lesions. Numerous mutations of the COL4A5 gene encoding the alpha 5-chain of type IV collagen have been described, establishing the molecular cause of AS. The goal of the present study was to identify the genotype-phenotype correlations that are helpful in clinical counseling. COL4A5-mutations (n=267) in males were analysed including 23 German Alport families. METHODS: Exons of the COL4A5 gene were PCR-amplified and screened by Southern blot, direct sequencing or denaturing gradient gel electrophoresis. Phenotypes were obtained by questionnaires or extracted from 44 publications in the literature. Data were analysed by Kaplan-Meier statistics, chi(2) and Kruskal-Wallis tests. RESULTS: Genotype-phenotype data for 23 German Alport families are reported. Analysis of these data and of mutations published in the literature showed the type of mutation being a significant predictor of end-stage renal failure (ESRF) age. The patients' renal phenotypes could be grouped into three cohorts: (1) large rearrangements, frame shift, nonsense, and splice donor mutations had a mean ESRF age of 19.8+/-5.7 years; (2) non-glycine- or 3' glycine-missense mutations, in-frame deletions/insertions and splice acceptor mutations had a mean ESRF age of 25.7+/-7.2 years and fewer extrarenal symptoms; (3) 5' glycine substitutions had an even later onset of ESRF at 30.1+/-7.2 years. Glycine-substitutions occurred less commonly de novo than all other mutations (5.5% vs 13.9%). However, due to the evolutionary advantage of their moderate phenotype, they were the most common mutations. The intrafamilial phenotype of an individual mutation was found to be very consistent with regards to the manifestation of deafness, lenticonus and the time point of onset of ESRF. CONCLUSIONS: Knowledge of the mutation adds significant information about the progress of renal and extrarenal disease in males with X-linked AS. We suggest that the considerable prognostic relevance of a patient's genotype should be included in the classification of the Alport phenotype.     

Clinical and genetic features in autosomal recessive and X-linked Alport syndrome

Background

This study determined the family history and clinical features that suggested autosomal recessive rather than X-linked Alport syndrome.

Methods

All patients had the diagnosis of Alport syndrome and the mode of inheritance confirmed by genetic testing, and underwent examination at a single centre.

Results

Patients comprised 9 males and 6 females with autosomal recessive Alport syndrome, and 18 males and 22 females with X-linked disease. Fourteen (93 %) individuals with autosomal recessive Alport syndrome developed early end-stage renal failure, all 15 had hearing loss, and most had lenticonus (12, 80 %), and a central (13, 87 %) or peripheral (13, 87 %) retinopathy. These features occurred as often as in males with X-linked disease. Females with autosomal recessive inheritance were less likely to have an affected family member in another generation (p?=?0.01) than females with X-linked disease. They were more likely to have renal failure (p?=?0.003), hearing loss (p?=?0.02) and lenticonus (p?<?0.001). Fifty percent had a central retinopathy compared with 18 % with X-linked disease (p?=?0.14), but peripheral retinopathy prevalence was not different (p?=?0.64). Nonsense mutations accounted for 67 % (8/12) of these disease-causing mutations.

Conclusions

Autosomal recessive inheritance is increased in females with Alport syndrome and early onset renal failure, hearing loss, lenticonus, and, possibly, central retinopathy.     

The use of ocular abnormalities to diagnose X-linked Alport syndrome in children

The diagnosis of X-linked Alport syndrome is often difficult, but the demonstration of lenticonus and retinopathy may facilitate the diagnosis in adult patients. The aim of this study was to determine the diagnostic usefulness of ocular examination in children. Fourteen families with at least one affected child were studied clinically, and COL4A5 mutations were determined. The families included 15 affected boys (median age 11 years, range 4-19 years). Two boys (13%) had renal failure, nine (60%) had a known hearing loss, one (7%) had lenticonus and five (33%) had a central (4/15, 27%) or peripheral (4/14, 29%) retinopathy. Lenticonus and retinopathy were first noted in 14 and 11 year olds, respectively. All boys with retinopathy had a hearing loss. The early onset retinopathy was associated with a severe mutation (Q1383X). Eight families (8/14, 57%) comprised only sons and mothers, and two mothers (2/12, 17%) had the retinopathy. Six boys (40%) would have been diagnosed with Alport syndrome on the basis of their own or their mother's ocular examinations. None of the six girls (median age 8 years, range 7-14 years) had ocular abnormalities. Hearing loss is usually highly sensitive for the diagnosis of Alport syndrome, but ocular examination of boys and their mothers at the initial consultation is a non-invasive test that is helpful in up to 40% cases.     

Alport综合征一家系中新的COL4A5基因突变

目的了解我国Ｘ伴性显性（ＸＤ）遗传Ａｌｐｏｒｔ综合征（ＡＳ）中ＣＯＬ４Ａ５基因突变特点。方法应用聚合酶链反应（ＰＣＲ）－变性梯度凝胶电泳（ＤＧＧＥ）和直接测序的方法，对来自７个ＸＤ－ＡＳ家系１０个成员和１００个正常人外周血ＤＮＡ标本进行了ＣＯＬ４Ａ５基因４３号外显子的检测。结果在一个家系中发现４１４２Ｃ→Ｔ（Ｐｒｏ１３１４Ｓｅｒ）的转换突变，先证者与其弟、其母均发现有此异常。结论表明该突变为一遗传     

Attitudes toward genetic diagnosis and prenatal diagnosis of X-linked Alport syndrome in China

Aim: Alport syndrome (AS) is a progressive renal disease characterized by hematuria and progressive renal failure. X‐linked dominant AS (XLAS) is the predominant inheritance form caused by mutations in COL4A5 gene. Attitudes toward genetic diagnosis and prenatal diagnosis for Chinese AS families were investigated. Attitudes toward genetic diagnosis and prenatal diagnosis in Chinese XLAS families were evaluated in the current study. Methods: A total of 160 XLAS patients and their 126 healthy family members in China were interviewed. After providing background knowledge counselling and education on AS, their attitudes toward genetic diagnosis and prenatal diagnosis were evaluated by multiple‐choice questionnaire. Results: Majority of the respondents cared mostly about the prognosis and treatment effects of AS (89.9% vs 81.1%) since they considered that the worst outcome of XALS was renal insufficiency (92.3%). Of all the interviewees, 99.3% were interested in genetic research for the discovery of better treatments and more appropriate diagnostic tools (positive attitudes) (89.5% vs 73.2%). About 80% of the participants would accept prenatal testing and subsequent termination of pregnancy in cases of affected foetuses (boys: 86.8% and girls: 74.6%, respectively). Conclusion: Most Chinese XLAS families show positive attitudes and desire new discoveries in treatment and diagnosis. About 80% of respondents would approve prenatal testing with a desire for selective termination of pregnancy rather than predicting the health of a future child.     

Sporadic case of X-chromosomal Alport syndrome in a consanguineous family

Alport syndrome (AS) is a genetic disorder of basement membranes caused by mutations in type IV collagen genes that is characterized by chronic hematuria and progressive nephropathy leading to renal failure. The main extrarenal features include sensorineural hearing loss and ocular lesions. The mode of inheritance is X-linked dominant in about 80%–85% of the affected families, whereas autosomal transmission is rarely encountered. We report a male patient originating from a healthy consanguineous Lebanese family who presented with an unusual association of obstructive uropathy and AS. Hematuria and proteinuria were initially attributed to a suspected poststreptococcal glomerulonephritis (GN) and high-grade subpelvic ureteral stenosis. Persistence of symptoms after medical treatment of poststreptococcal GN and surgical correction of obstructive uropathy finally led to renal biopsy. The observed ultrastructural changes of the glomerular basement membrane were typical for AS.Molecular genetic studies revealed a previously undescribed de novo mutation in the COL4A5 gene, excluding maternal heterozygotic carrier status. This case report emphasizes the importance of hereditary nephritis in the differential diagnosis of chronic hematuria, and demonstrates the value of molecular studies for genetic counselling in AS. Received: 9 October 1998 / Revised: 15 February 1999 / Accepted: 24 August 1999