Familial focal segmental glomerulosclerosis: nine cases in four families and review of the literature

Two new families with hereditary minimal change disease

BACKGROUND

Steroid-sensitive idiopathic nephrotic syndrome (SSINS) is most often encountered in sporadic cases of minimal change disease (MCD). Only rare cases of familial forms of MCD have been reported and most of them only in one generation. The scarcity of data has precluded unraveling the underlying genetic defect and candidate gene approaches have been unsuccessful. Here we report two families with related SSINS cases and review the related literature.

CASE PRESENTATION

Two siblings and a cousin (first family), and a father and his son (second family), are reported with SSINS due to MCD. Patients have been followed up for more than 12 years and a renal biopsy was performed in three cases, demonstrating typical features of MCD. The course of the disease was remarkable because of several relapses treated with steroids. In three cases, mycophenolate mofetil or cyclosporine was added.

CONCLUSION

Familial SSINS due to MCD is extremely rare and no genetic defect has been identified so far. Reporting cases of hereditary MCD will allow further genetic studies which will ultimately help unravel the molecular basis of this disease.

Integrating human and rodent data to identify the genetic factors involved in chronic kidney disease

The increasing numbers of patients with chronic kidney disease combined with no satisfying interventions for preventing or curing the disease emphasize the need to better understand the genes involved in the initiation and progression of complex renal diseases, their interactions with other host genes, and the environment. Linkage and association studies in human, rat, and mouse have been successful in identifying genetic loci for various disease-related phenotypes but have thus far not been very successful identifying underlying genes. The purpose of this review is to summarize the progress in human, rat, and mouse genetic studies to show the concordance between the loci among the different species. The collective utilization of human and nonhuman mammalian datasets and resources can lead to a more rapid narrowing of disease loci and the subsequent identification of candidate genes. In addition, genes identified through these methods can be further characterized and investigated for interactions using animal models, which is not possible in humans.

Familial glomerulonephropathy in the Bullmastiff

Glomerular disease was diagnosed by histopathologic examination in 11 related Bullmastiff dogs, and clinical and laboratory data were collected retrospectively. Four female and seven male dogs between the ages of 2.5 and 11 years were affected. Clinical signs, including lethargy and anorexia, were nonspecific and occurred shortly before death or euthanasia. In five affected dogs serial blood samples were obtained, and dramatically elevated blood urea nitrogen and creatinine levels were demonstrated up to 2.75 years before death. Protein-creatinine ratios were elevated in six of six dogs and were above normal 3.5 years before death in one dog. The kidneys appeared grossly normal to slightly smaller than normal at necropsy. Histologic abnormalities of the kidneys were consistent with chronic glomerulonephropathy with sclerosis. Examination of the pedigrees of related affected dogs yielded evidence supporting an autosomal recessive mode of inheritance.

The focal segmental glomerulosclerosis permeability factor: biochemical characteristics and biological effects

Focal segmental glomerulosclerosis (FSGS) is characterized by steroid resistant nephrotic syndrome and progression to end-stage renal disease. Proteinuria in certain patients with FSGS may be caused by a circulating factor (FSGS permeability factor [FSPF]). The current report documents the biochemical characteristics and the biological and molecular effects of 70% ammonium sulfate supernatant of plasma from patients with recurrence of FSGS after transplantation (FSGS 70% supernatant). FS permeability activity, defined as the capacity of plasma from patients with FSGS to increase albumin permeability (P(alb)) of isolated glomeruli, was assessed in vitro. Permeability activity was not affected by lyophilization. FSPF bound strongly to matrices containing Mono-Q anion exchanger or protein A. It eluted from matrix-bound Cibacron blue F3GA over a wide range of salt concentrations, indicating a potential binding with other proteins, such as albumin. FSPF caused a maximal increase in P(alb) within 2 mins of incubation in vitro. Cellular proteins isolated from glomeruli with increased P(alb) showed decreased tyrosine phosphorylation of focal adhesion kinase, paxillin, and other proteins. Tyrosine phosphatase ]inhibition prevented the increase in P(alb). Intravenous administration of as little as 3 mg protein in FSGS 70% supernatant increased P(alb), while 9 mg or more were required to produce proteinuria. We conclude that FSPF is a low-molecular-weight protein, carries an anionic charge, and binds to protein A. Effects of FSPF on the glomerular permeability barrier are rapid and dose dependent and involve signaling through altered phosphorylation of cellular proteins. Identification of these biochemical and biological characteristics may be used to design strategies for removing FSPF from circulation and for purification and identification of this factor.

The genetic basis of FSGS and steroid-resistant nephrosis

Studies of Mendelian forms of focal segmental glomerulosclerosis (FSGS) and nephrotic syndrome have provided new insights into the mechanism of these diseases. Congenital nephrotic syndrome and familial forms of FSGS form a spectrum of podocyte diseases of varying severity and age of onset. Mutations in both nephrin gene (NPHS1) alleles lead to congenital nephrosis, podocyte foot process efacement, and loss of slit-diaphragm structure. Mutations in both podocin gene (NPHS2) alleles lead to a wide range of human disease, from childhood-onset steroid-resistant FSGS and minimal change disease to adult-onset FSGS. Dominantly inherited mutations in ACTN4, the alpha-actinin-4 gene, can lead to a slowly progressive adult-onset form of FSGS. In addition, FSGS is observed as part of several rare multisystem inherited syndromes. Here we review recent progress in understanding the genetic basis of FSGS in humans.

Familial collapsing glomerulopathy: clinical, pathological and immunogenetic features

BACKGROUND

Collapsing glomerulopathy (CG) is an aggressive form of glomerular injury frequently seen in association with HIV infection, although it is also recognized in non-HIV patients as a primary disease. Until now, the occurrence of CG in a familial pattern has not been reported.

METHODS

We studied five members of a family (siblings), admitted for evaluation of proteinuria and nephrotic syndrome. They had no other family history of renal disease. Blood samples for major histocompatibility complex (MHC) analysis were obtained from the five siblings, both parents and four relatives.

RESULTS

Renal biopsy performed in four out of the five siblings revealed capillary collapse and retraction with visceral epithelial cell swelling and reabsorption droplets, consistent with CG. Two of the patients had suggestive symptoms of systemic lupus erythematosus, such as arthritis, rash, hair loss, moderate leukopenia and lymphopenia, low titers of antinuclear antibodies (ANA) and anti-SSA/Ro antibodies, but no immune complex deposition on renal biopsy. IgG serology for parvovirus B19 (PVB-19) was positive only in two siblings but polymerase chain reaction (PCR) was negative. Immunogenetic analysis showed that all patients shared the same MHC haplotype inherited from the mother.

CONCLUSIONS

CG can present in a familial pattern. Since a similar MHC haplotype was observed in affected and non-affected members of the family, we conclude that the environment plays an important role in the development of the disease.

Familial focal segmental glomerulosclerosis

There is increasing recognition of the importance of genetic factors in the development of focal segmental glomerulosclerosis and related proteinuric disorders. Recently, four genes have been identified which, when defective, cause focal segmental glomerulosclerosis or nephrosis. All of these genes appear to be important in the maintenance of glomerular podocyte function. However, not all cases of familial nephrosis or proteinuria are explained by defects in these genes.

Familial nephropathy differing from minimal change nephropathy and focal glomerulosclerosis

BACKGROUND

Nephrotic syndrome in childhood is mainly due to minimal change nephropathy. In general, it is characterized by selective proteinuria, by steroid responsiveness, and histologically by podocytic foot process effacement. Familial presentation is rare and mainly restricted to one generation.

METHODS

We describe the occurrence of a familial nephropathy in a mother and two daughters. An initial diagnosis of minimal change nephropathy was made, but subsequently unique features became apparent. During follow-up, detailed studies of renal function and urinary protein excretion were performed. Available frozen renal biopsy material was revised and processed for immunofluorescence to detect abnormalities in the expression of heparan sulfate proteoglycans. The latter results were compared with renal biopsies of a control group composed of five adult patients with minimal change nephropathy.

RESULTS

The mother and two daughters were proteinuric since their early childhood. The mother revealed a persistent nephrotic syndrome for more than 20 years despite treatment with various immunosuppressive drugs. Likewise, treatment with prednisone was ineffective in the daughters. All three patients retained normal renal function during follow-up. Detailed measurements revealed that the proteinuria was incredibly selective (selectivity index approximately 0.01), and there was no evidence of tubulointerstitial damage, as reflected by a normal excretion of the low-molecular weight proteins beta(2)-microglobulin and alpha1-microglobulin. Renal biopsy performed in the mother and one daughter was thought to be compatible with minimal change nephropathy. However, histologically, two remarkable findings were made. By electron microscopy, there was no evidence of foot process retraction; specifically, the foot process width and slit pore diameter were normal. Furthermore, in contrast to the control patients, the expression of heparan sulfate polysaccharide side chains, as reflected by the staining with monoclonal antibody JM403, was normal.

CONCLUSIONS

We propose that this family represents a new familial nephropathy. The molecular basis of the permeability defect remains to be identified.

A locus for an autosomal dominant form of progressive renal failure and hypertension at chromosome 1q21

Linkage studies were performed in a large family with an autosomal dominant phenotype characterized by nephropathy and hypertension. In this family of Iraqi Jewish origin, the nephropathy develops into progressive renal failure. By performing a genomewide linkage search, we localized the disease gene to chromosome 1q21; the highest LOD score was obtained for the marker at locus D1S305, which yielded a maximum LOD score of 4.71 at a recombination fraction of 0. Recombination mapping defined an interval of approximately 11.6 cM, between the markers at loci D1S2696 and D1S2635, that contains the disease gene. Localization of the disease-causing gene in this family represents a necessary step toward isolation of the defective gene and toward a deeper understanding of the mechanisms of hypertension and progressive renal failure.

Mother-to-child transmitted WT1 splice-site mutation is responsible for distinct glomerular diseases

Mutations in the Wilms' tumor suppressor gene (WT1) are linked with Denys-Drash syndrome (DDS), a rare childhood disease characterized by diffuse mesangial sclerosis and renal failure of early onset, XY pseudohermaphroditism, and high risk of Wilms' tumor. KTS (lysine-threonine-serine) splice site mutations in WT1 intron 9 have been described in patients with Frasier syndrome, another rare syndrome defined by focal and segmental glomerulosclerosis (FSGS), XY pseudohermaphroditism, and frequent occurrence of gonadoblastoma. Cases of Frasier syndrome raise the question whether splice site mutations may also be found in XX females with isolated FSGS. A girl (index case) presented with the nephrotic syndrome at 9 mo of age. The diagnosis of DDS was based on the finding of diffuse mesangial sclerosis in the kidney biopsy and of a XY karyotype. The index case's mother had had proteinuria since she was 6 years of age. A renal biopsy was performed when she was 28 and disclosed FSGS. The same splice site mutation in intron 9 (WT1 1228+5 G-->A) involving one allele was found in the child and in her mother, but not in other members of the kindred (including the parents, the two brothers, and the two sisters of the index case's mother) who were free of renal symptoms. Quantification of WT1 +KTS/-KTS isoforms in the index case's father and one index case's maternal uncle showed a normal +KTS/-KTS ratio of 1.50. In contrast, the index case and her mother had a low ratio (0.40 and 0.34, respectively), within the range reported in Frasier syndrome. In conclusion, this study shows that the KTS splice site mutation is not specific for Frasier syndrome, but that it can also be found in DDS and in a normal female (XX) with FSGS, a woman who achieved normal pregnancy. It is suggested that WT1 splice site mutations should be sought in phenotypically normal females who present with FSGS or with related glomerulopathies of early onset.

A locus for inherited focal segmental glomerulosclerosis maps to chromosome 19q13

We performed a genome-wide linkage analysis search for a genetic locus responsible for kidney dysfunction in a large family. This inherited condition, characterized by proteinuria, progressive renal insufficiency, and focal segmental glomerulosclerosis, follows autosomal dominant inheritance. We show with a high degree of certainty (maximum 2-point lod score 12.28) that the gene responsible for this condition is located on chromosome 19q13.