[Fechtner syndrome, a nonmuscle myosin heavy chain 9 gene mutation related disease: a case report and literature review]

OBJECTIVE

To improve the recognition of Fechtner syndrome.

METHODS

The clinical and laboratory data and family survey of a patient with Fechtner's syndrom was reported.

RESULTS AND CONCLUSION

Giant platelets, thrombocytopenia and characteristic granulocyte inclusion bodies (Döhle-like bodies) were found in both peripheral blood and bone marrow smears of the patient. Clinically the patient had renal damage, nervous deafness, and vitreous lesions. There was a family genetic tendency on family survey the diagnosis of Fechtner syndrome is established.

Alphav beta6 integrin regulates renal fibrosis and inflammation in Alport mouse

The transforming growth factor (TGF)-beta-inducible integrin alpha v beta6 is preferentially expressed at sites of epithelial remodeling and has been shown to bind and activate latent precursor TGF-beta. Herein, we show that alpha v beta6 is overexpressed in human kidney epithelium in membranous glomerulonephritis, diabetes mellitus, IgA nephropathy, Goodpasture's syndrome, and Alport syndrome renal epithelium. To assess the potential regulatory role of alpha v beta6 in renal disease, we studied the effects of function-blocking alpha v beta6 monoclonal antibodies (mAbs) and genetic ablation of the beta6 subunit on kidney fibrosis in Col4A3-/- mice, a mouse model of Alport syndrome. Expression of alpha v beta6 in Alport mouse kidneys was observed primarily in cortical tubular epithelial cells and in correlation with the progression of fibrosis. Treatment with alpha v beta6-blocking mAbs inhibited accumulation of activated fibroblasts and deposition of interstitial collagen matrix. Similar inhibition of renal fibrosis was observed in beta6-deficient Alport mice. Transcript profiling of kidney tissues showed that alpha v beta6-blocking mAbs significantly inhibited disease-associated changes in expression of fibrotic and inflammatory mediators. Similar patterns of transcript modulation were produced with recombinant soluble TGF-beta RII treatment, suggesting shared regulatory functions of alpha v beta6 and TGF-beta. These findings demonstrate that alpha v beta6 can contribute to the regulation of renal fibrosis and suggest this integrin as a potential therapeutic target.

Autosomal-dominant Alport syndrome: natural history of a disease due to COL4A3 or COL4A4 gene

BACKGROUND

Alport syndrome is a clinically and genetically heterogeneous nephropathy. The majority of cases are transmitted as an X-linked semidominant condition due to COL4A5 mutations. In this form males are more severely affected than females. Less than 10% of cases are autosomal recessive due to mutation in either COL4A3 or COL4A4. In this rarer form, both males and females are severely affected. Only two cases of autosomal-dominant Alport syndrome have been reported, one due to a COL4A3 mutation and the other due to a COL4A4 mutation. Because of the paucity of the reported families, the natural history of autosomal-dominant Alport syndrome is mostly unknown.

METHODS

Four families with likely autosomal-dominant Alport syndrome were investigated. COL4A3 and COL4A4 genes were analyzed by denaturing high-performance liquid chromatography (HPLC). Automated sequencing was performed to identify the underlying mutation.

RESULTS

Two families had a mutation in the COL4A4 gene and two in the COL4A3. Accurate clinical evaluation of family members showed interesting results. Affected individuals (22 persons) had a wide range of phenotypes from end-stage renal disease (ESRD) in the fifth decade to a nonprogressive isolated microhematuria. Finally, three heterozygous individuals (90, 22 and 11 years old, respectively) were completely asymptomatic.

CONCLUSION

This paper demonstrated that patients affected by autosomal-dominant Alport syndrome have a high clinical variability. Moreover, a reduced penetrance of about 90% (3 of 25) may be considered for the assessment of recurrence risk during genetic counseling of these families.

[Contribution of genetics to knowledge and management of hereditary kidney diseases progressing to renal failure]

Genes of most of the hereditary renal diseases progressing to renal insufficiency are now identified. In the first part of this paper we describe their multi-faceted genetics. Genetic heterogeneity has been demonstrated in many of these diseases, such as Alport's syndrome and nephronophtisis. In some of them an allelic heterogeneity is present as in the X-linked form of Alport's syndrome (more than 300 different mutations have been described along the COL4A5 gene). Besides these classical mendelian diseases, mendelian subentities have been isolated within common diseases such as cortico-resistant nephrosis. Many diseases also demonstrate a variability of their phenotype resulting from allelic and/or genetic heterogeneity, or from modifier genes. In the second part of the paper we discuss the consequences of this explosion of knowledge with respect to epidemiology, genetic diagnosis, prenatal diagnosis and treatment.

Integrin alpha1beta1 and transforming growth factor-beta1 play distinct roles in alport glomerular pathogenesis and serve as dual targets for metabolic therapy

Alport syndrome is a genetic disorder resulting from mutations in type IV collagen genes. The defect results in pathological changes in kidney glomerular and inner-ear basement membranes. In the kidney, progressive glomerulonephritis culminates in tubulointerstitial fibrosis and death. Using gene knockout-mouse models, we demonstrate that two different pathways, one mediated by transforming growth factor (TGF)-beta1 and the other by integrin alpha1beta1, affect Alport glomerular pathogenesis in distinct ways. In Alport mice that are also null for integrin alpha1 expression, expansion of the mesangial matrix and podocyte foot process effacement are attenuated. The novel observation of nonnative laminin isoforms (laminin-2 and/or laminin-4) accumulating in the glomerular basement membrane of Alport mice is markedly reduced in the double knockouts. The second pathway, mediated by TGF-beta1, was blocked using a soluble fusion protein comprising the extracellular domain of the TGF-beta1 type II receptor. This inhibitor prevents focal thickening of the glomerular basement membrane, but does not prevent effacement of the podocyte foot processes. If both integrin alpha1beta1 and TGF-beta1 pathways are functionally inhibited, glomerular foot process and glomerular basement membrane morphology are primarily restored and renal function is markedly improved. These data suggest that integrin alpha1beta1 and TGF-beta1 may provide useful targets for a dual therapy aimed at slowing disease progression in Alport glomerulonephritis.

Type IV collagen of the glomerular basement membrane. Evidence that the chain specificity of network assembly is encoded by the noncollagenous NC1 domains

The ultrafiltration function of the glomerular basement membrane (GBM) of the kidney is impaired in genetic and acquired diseases that affect type IV collagen. The GBM is composed of five (alpha1 to alpha5) of the six chains of type IV collagen, organized into an alpha1.alpha2(IV) and an alpha3.alpha4.alpha5(IV) network. In Alport syndrome, mutations in any of the genes encoding the alpha3(IV), alpha4(IV), and alpha5(IV) chains cause the absence of the alpha3. alpha4.alpha5 network, which leads to progressive renal failure. In the present study, the molecular mechanism underlying the network defect was explored by further characterization of the chain organization and elucidation of the discriminatory interactions that govern network assembly. The existence of the two networks was further established by analysis of the hexameric complex of the noncollagenous (NC1) domains, and the alpha5 chain was shown to be linked to the alpha3 and alpha4 chains by interaction through their respective NC1 domains. The potential recognition function of the NC1 domains in network assembly was investigated by comparing the composition of native NC1 hexamers with hexamers that were dissociated and reconstituted in vitro and with hexamers assembled in vitro from purified alpha1-alpha5(IV) NC1 monomers. The results showed that NC1 monomers associate to form native-like hexamers characterized by two distinct populations, an alpha1.alpha2 and alpha3.alpha4.alpha5 heterohexamer. These findings indicate that the NC1 monomers contain recognition sequences for selection of chains and protomers that are sufficient to encode the assembly of the alpha1.alpha2 and alpha3.alpha4.alpha5 networks of GBM. Moreover, hexamer formation from the alpha3, alpha4, and alpha5 NC1 monomers required co-assembly of all three monomers, suggesting that mutations in the NC1 domain in Alport syndrome may disrupt the assembly of the alpha3.alpha4.alpha5 network by interfering with the assembly of the alpha3.alpha4.alpha5 NC1 hexamer.

Role for transforming growth factor-beta1 in alport renal disease progression

BACKGROUND

Alport syndrome results from mutations in either the alpha3(IV), alpha4(IV), or alpha5(IV) collagen genes. The disease is characterized by a progressive glomerulonephritis usually associated with a high-frequency sensorineural hearing loss. A mouse model for an autosomal form of Alport syndrome [collagen alpha3(IV) knockout] was produced and characterized. In this study, the model was exploited to demonstrate a potential role for transforming growth factor-beta1 (TGF-beta1) in Alport renal disease pathogenesis.

METHODS

Kidneys from normal and Alport mice, taken at different stages during the course of renal disease progression, were analyzed by Northern blot, in situ hybridization, and immunohistology for expression of TGF-beta1 and components of the extracellular matrix. Normal and Alport human kidney was examined for TGF-beta1 expression using RNase protection.

RESULTS

The mRNAs encoding TGF-beta1 (in both mouse and human), entactin, fibronectin, and the collagen alpha1(IV) and alpha2(IV) chains were significantly induced in total kidney as a function of Alport renal disease progression. The induction of these specific mRNAs was observed in the glomerular podocytes of animals with advanced disease. Type IV collagen, laminin-1, and fibronectin were markedly elevated in the tubulointerstitium at 10 weeks, but not at 6 weeks, suggesting that elevated expression of specific mRNAs on Northern blots reflects events associated with tubulointerstitial fibrosis.

CONCLUSIONS

The concomitant accumulation of mRNAs encoding TGF-beta1 and extracellular matrix components in the podocytes of diseased kidneys may reflect key events in Alport renal disease progression. These data suggest a role for TGF-beta1 in both glomerular and tubulointerstitial damage associated with Alport syndrome.

Benign familial hematuria due to mutation of the type IV collagen alpha4 gene

Benign familial hematuria (BFH) is characterized by autosomal dominant inheritance, thinning of the glomerular basement membrane (GBM) and normal renal function. It is frequent in patients with persistent microscopic hematuria, but cannot be clinically differentiated from the initial stages of Alport syndrome, a severe GBM disorder which progresses to renal failure. We present here linkage of benign familial hematuria with the COL4A3 and COL4A4 genes at 2q35-37 (Zmax = 3.58 at theta = 0.0). Subsequently, a glycine to glutamic acid substitution was identified in the collagenous region of the COL4A4 gene. We conclude that type IV collagen defects cause both benign hematuria and Alport syndrome. Furthermore, our data suggest that BFH patients can be carriers of autosomal recessive Alport syndrome.

Clinical features and pathogenesis of Alport retinopathy

BACKGROUND

Alport syndrome refers to the clinical triad of hereditary nephritis, sensorineural deafness, and ocular abnormalities. Ultrastructural findings in the lens capsule and in the renal glomeruli have provided evidence that abnormal basement membranes are elaborated in affected tissues of patients with this disorder. Recently, the results of several linkage studies have allowed the genetic defect in Alport syndrome to be mapped to a locus that codes for a subtype of type IV collagen (alpha 5) known to be present in glomerular basement membranes. In spite of these advances, the nature of the retinal flecks in Alport syndrome and the visual consequences of the flecks remain controversial.

METHODS

Detailed psychophysical and electrophysiologic testing was performed in a young man with Alport syndrome. The concurrence of an unusually extensive fleck retinopathy and unilateral pseudophakia afforded a unique opportunity to assess the effect of the flecks on retinal function.

RESULTS

No sensory deficits were present in the eye with clear media.

CONCLUSION

Macular flecks in Alport syndrome are not associated with demonstrable retinal dysfunction. The authors address questions about the nature and pathogenesis of the flecks in light of new clinical and genetic information.

[Alport's syndrome]

After a historical introduction the authors analyze contemporary views on the aetiology, pathogenesis and genetics, they characterize the clinical picture and histopathological findings in Alport's syndrome. They emphasize that Alport's syndrome is more frequent than generally reported and that it deserves therefore appropriate attention in the differential diagnosis of renal diseases. They draw attention to the results of most recent genetic research which makes it possible to detect gene carriers of Alport's syndrome as well as early prenatal and postnatal diagnosis of this most frequently progressing hereditary nephritis.

The pathogenesis of Alport syndrome involves type IV collagen molecules containing the alpha 3(IV) chain: evidence from anti-GBM nephritis after renal transplantation

Mutations in the COL4A5 collagen gene have been implicated as the primary defect in Alport syndrome, a heritable disorder characterized by sensorineural deafness and glomerulonephritis that progresses to end-stage renal failure. In the present study, the molecular nature of the defect in Alport glomerular basement membrane (GBM) was explored using anti-GBM alloantibodies (tissue-bound and circulating) produced in three Alport patients subsequent to renal transplantation. The alloantibodies bound to the alpha 3(IV)NC1 domain of type IV collagen and not to any other basement membrane component. In tissue sections, the alloantibodies bound specifically to peripheral GBM in normal kidney and the affected renal transplant but not to that of Alport kidney. These results establish that: the alpha 3 chain in type IV collagen molecules, the Goodpasture autoantigen, is the target alloantigen in post-transplant anti-GBM nephritis in patients with Alport syndrome, and that a molecular commonality exists in the pathogenesis of anti-GBM nephritis causing loss of renal allografts in patients with Alport syndrome and renal failure in patients with Goodpasture syndrome. These findings implicate: (1) defective assembly of type IV collagen molecules containing the alpha 3(IV) chain in Alport GBM; and (2) the existence of a mechanism linking the assembly of molecules containing the alpha 3(IV) chain with those containing the alpha 5(IV) chain.

Alport's syndrome

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[Nephropathy and deafness (Alport syndrome) without positive family history (author's transl)]

This is a report of a 22-year-old man affected with hereditary nephropathy and deafness (Alport syndrome) without positive family history. The diagnosis is based on the typical clinical history, presence of symmetrical neural deafness, and terminal stage of renal insufficiency, that could not be classified otherwise following renal biopsy. The differential diagnosis and genetics are discussed.

Hereditary nephropathy with hematuria (Alport's syndrome)

Among 82 members and four generations of a French-Canadian family, 14 cases of hereditary nephropathy (Alport's syndrome) were documented. Five additional members of the family had died, probably because of this same illness. Deafness occurred in five family members with nephropathy and in one without renal disease. Ten of 12 affected males died in uremia before they had reached the age of 40 years. One of seven affected females died following a pregnancy. In two surviving patients, special investigations failed to elicit intrinsic tubular defects such as amino-aciduria, renal tubular acidosis, hyperphosphaturia or renal glucosuria. Systemic illness such as abnormal aminoacids in serum, primary hyperoxaluria, diabetes mellitus and infections were also excluded. Immunological defects were not demonstrable and the staining of renal biopsy tissue with fluorescein-labelled anti-beta(1)c, anti-IgG and antifibrinogen was negative. Renal tissue material of early, advanced and terminal hereditary nephropathy showed both tubular and interstitial, vascular and glomerular lesions. Electronmicroscopy showed marked thickening of tubular and glomerular basement membranes, increase of mesangial tissue and fusion of foot processes but failed to demonstrate "immune deposits." It is postulated therefore that hereditary nephropathy results from an inborn error of metabolism where an as yet unidentified metabolite damages the renal tissue as well as the acoustic nerve, analogous perhaps to the action of certain drugs, e.g. nephro-ototoxic antibiotics.