A locus for adolescent and adult onset familial focal segmental glomerulosclerosis on chromosome 1q25-31

Genetic background in the rat affects endocrine and metabolic outcomes of bisphenol F exposure

Environmental bisphenol compounds like bisphenol F (BPF) are endocrine-disrupting chemicals (EDCs) affecting adipose and classical endocrine systems. Genetic factors that influence EDC exposure outcomes are poorly understood and are unaccounted variables that may contribute to the large range of reported outcomes in the human population. We previously demonstrated that BPF exposure increased body growth and adiposity in male N/NIH heterogeneous stock (HS) rats, a genetically heterogeneous outbred population. We hypothesize that the founder strains of the HS rat exhibit EDC effects that were strain- and sex-dependent. Weanling littermate pairs of male and female ACI, BN, BUF, F344, M520, and WKY rats randomly received either vehicle (0.1% EtOH) or 1.125 mg BPF/l in 0.1% EtOH for 10 weeks in drinking water. Body weight and fluid intake were measured weekly, metabolic parameters were assessed, and blood and tissues were collected. BPF increased thyroid weight in ACI males, thymus and kidney weight in BUF females, adrenal weight in WKY males, and possibly increased pituitary weight in BN males. BUF females also developed a disruption in activity and metabolic rate with BPF exposure. These sex- and strain-specific exposure outcomes illustrate that HS rat founders possess diverse bisphenol-exposure risk alleles and suggest that BPF exposure may intensify inherent organ system dysfunction existing in the HS rat founders. We propose that the HS rat will be an invaluable model for dissecting gene EDC interactions on health.

A novel mutation in NPHS2 gene identified in a Chinese pedigree with autosomal recessive steroid-resistant nephrotic syndrome

AIMS

Steroid-resistant nephrotic syndrome (SRNS) is an inherent deficiency of podocyte caused by mutations of genes encoding slit diaphragm proteins. Mutations in NPHS2, encoding podocin, have been identified as responsible for childhood-onset familial SRNS. The present study revealed the genotype of a Chinese pedigree with autosomal recessive (AR) SRNS and reported a novel disease-causing NPHS2 mutation.

METHODS

A Chinese pedigree with AR-SRNS was enrolled in the study. All eight exons and exon-intron boundaries of NPHS2 genes were amplified from the genomic DNA of the family members and analysed by direct sequencing. The deficient expression of the mutant protein was illustrated by indirect immunofluorescence.

RESULTS

A compound heterozygous NPHS2 mutation (c.211C > T /c.460dupT) was found in the proband. The paternal c.211C > T is a novel point mutation, resulting in an immediate stop codon (p.Arg71X). The maternal c.460dupT is a frameshift mutation introducing an earlier stop codon (p.Phe156AspfsX10). Both mutations could be expected to lead to truncated protein of podocin. Abnormal expression and distribution of the mutated protein were also exhibited in the patient.

CONCLUSIONS

The compound heterozygous mutation in NPHS2 may explain the development of SRNS in this family. p.Arg71X is a novel disease-causing mutation leading to a deficient expression of podocin.

Serum cystatin C level, kidney disease markers, and incidence of age-related macular degeneration: the Beaver Dam Eye Study

OBJECTIVE

To examine the associations of the serum cystatin C level and chronic kidney disease with the incidence of age-related macular degeneration (AMD) over 15 years.

METHODS

In this population-based cohort study of 4926 individuals aged 43 to 86 years at baseline, 3779 participated in 1 or more follow-up examinations. Age-related macular degeneration was determined by grading photographs of the macula. Individuals were defined as having mild or moderate to severe chronic kidney disease based on a value of more than 45 mL/min/1.73 m(2) to 60 mL/min/1.73 m(2) or less and 45 mL/min/1.73 m(2) or less, respectively, according to the Modification of Diet in Renal Disease Study equation.

RESULTS

While controlling for age and other risk factors, the level of serum cystatin C at baseline was associated with the incidence of early AMD (odds ratio per log standard deviation [95% confidence interval], 1.16 [1.01-1.35]) and exudative AMD (1.42 [1.03-1.96]) but not geographic atrophy (0.89 [0.56-1.41]) or progression of AMD (1.02 [0.88-1.18]). Mild chronic kidney disease was associated with the 15-year cumulative incidence of early AMD (odds ratio per log standard deviation, 1.36 [95% confidence interval, 1.00-1.86]) but not the incidence of other AMD end points.

CONCLUSION

There is a relationship between the level of serum cystatin C and chronic kidney disease with the incidence of AMD. The underlying biological processes remain to be determined.

Complement factor H polymorphisms, renal phenotypes and age-related macular degeneration: the Blue Mountains Eye Study

Complement factor H (CFH) is a key regulator of the alternative pathway of complement and its mutations have been associated with membranoproliferative glomerulonephritis type II, atypical hemolytic uremic syndrome and age-related macular degeneration (AMD), suggesting that alternative pathway dysregulation is a common pathogenetic feature of these ocular and renal conditions. In this study we tested the hypothesis that common CFH variants have a global role in renal function in the Australian population-based Blue Mountains Eye Study (BMES). We replicated the association of I62V with estimated glomerular filtration rate (GFR; P=0.017) and creatinine clearance (CRCL; P=0.015). The minor allele of I62V (G) was deleterious: adding one copy of the G allele decreased GFR/CRCL by approximately 0.98 ml min(-1) per 1.73 m(2) (95% confidence interval (CI): 0.97, 0.99). We also replicated the association of Y402H with AMD and provided an unbiased estimate of population attributable risk (PAR). The minor allele of Y402H (C) was deleterious: the odds ratio estimate of CC genotype compared to TT was 1.87 (95% CI: 1.44, 2.45). The PAR of the C allele was estimated as 0.22 (95% CI: 0.15, 0.28). In summary, in the BMES population we confirmed the association between I62V and renal function, as measured by the estimated GFR, plus the association of Y402H with both early- and late-stage AMD.

Complement factor H and hemicentin-1 in age-related macular degeneration and renal phenotypes

In this study, we investigated the associations of complement factor H (CFH) and hemicentin-1 (HMCN1) with age-related macular degeneration (AMD) and renal function. Three scales, measuring the course of AMD and drusen development, were examined in two samples: the Family Age-Related Macular degeneration Study (FARMS), consisting of families ascertained through a single individual with severe AMD, and an unascertained population-based family cohort, the Beaver Dam Eye Study (BDES), which was also used to assess longitudinal changes in AMD and associations with renal function. Associations were performed by a regression accounting for known risk factors as well as familial and sibling effects. Strong evidence of the association of rs1061170 (Y402H) variation with AMD was confirmed (P = 9.15 x 10(-5) in BDES, P = 0.016 in FARMS). This association was observed in multiple AMD scales, suggesting that its role is not phenotype-specific. Polymorphisms in both CFH and HMCN1 appeared to influence the longitudinal rate of change of AMD. The rs1061170 polymorphism was also associated with a reduction in estimated glomerular filtration rate (eGFR) (P = 0.046). Another CFH polymorphism, rs800292, was similarly associated with eGFR [beta = -0.90 (P = 0.022)]. Associations between rs743137 (P = 0.05) and rs680638 (P = 0.022) in HMCN1 with calculated creatinine clearance progression were also observed. Both genes appear to play a role in both AMD and renal pathophysiology. These findings support evidence for common pathways influencing ocular and renal function and suggest that further work is required on their common determinants.

Recessive NPHS2 (Podocin) mutations are rare in adult-onset idiopathic focal segmental glomerulosclerosis

Recessive NPHS2 (podocin) mutations account for up to approximately 30% of steroid-resistant idiopathic FSGS in children and are associated with a reduced risk for disease recurrence after renal transplantation. R229Q, a missense variant that is present in 3.6% of the white population, has been implicated as a common disease-causing mutation. Given these clinical implications, we examined the role of NPHS2 mutations in a cohort of patients with adult-onset FSGS. We used denaturing HPLC to screen for heterozygous and homozygous gene variants in PCR-amplified DNA fragments that contained all exons and splice junctions of NPHS2. Bidirectional sequencing was performed to define all of the gene variants detected. With the use of the denaturing HPLC in a single-blind pilot study, 40 of 43 known NPHS2 mutations were detected from 22 pediatric patients with FSGS to establish a test sensitivity of 93%. This screen then was applied to 87 adult patients with idiopathic FSGS (15 steroid-sensitive, 63 steroid-resistant, and nine familial cases). In this latter cohort, compound heterozygous mutations were detected only in one patient with steroid-sensitive FSGS (R229Q and Q285fsX302) and no homozygous mutations. Overall, R229Q accounted for eight (80%) of ten of the putative mutant alleles that were detected in the study cohort. Contrary to the pediatric experience, recessive NPHS2 mutations are rare in this study population, suggesting that the pathogenesis of FSGS in adults may differ from that in children. These data do not support R229Q as a disease-causing mutation for steroid-resistant FSGS.

Mouse model for acute bacterial prostatitis in genetically distinct inbred strains

OBJECTIVES

Prostatitis is a common urologic disease seen in adult men. As many as 50% of men will experience an episode of prostatitis in their lifetime, and 2% to 3% of men will have bacterial prostatitis. Because the pathogenic mechanisms of prostatitis remain unclear, we developed a reproducible mouse model of bacterial prostatitis in which to study the etiology and host factors associated with infection susceptibility.

METHODS

Male BALB/c, C3H/HeJ, C3H/HeOuJ, C57BL/6J, and (BALB/c x C3H/HeJ)F1 mice 13 weeks old were inoculated intraurethrally with 2 x 10(6) or 2 x 10(8) Escherichia coli. Control mice were inoculated with phosphate-buffered saline. The animals were killed at 5 days after inoculation to assess the intensities of the bladder and prostate infections.

RESULTS

Significant bladder or prostate infections were not present in the BALB/c, C57BL/6J, or (BALB/c x C3H/HeJ)F1 mice at either inoculum dose. In contrast, both C3H/HeJ and C3H/HeOuJ mice developed high bladder infections and severe, acute prostatitis at both doses. Control mice infected with phosphate-buffered saline had no bladder or prostate infections. The P values were less than 0.01 for the comparison of bladder and prostate colony-forming units between C3H/HeJ or C3H/HeOuJ and BALB/c, C57BL/6J, or F1 mice.

CONCLUSIONS

The strain-dependent differences in susceptibility indicate that genetic factors may play a major role in the etiology of bacterial prostatitis. Because F1 mice did not develop significant bladder and prostate infections, similar to the BALB/c parents, it appears that infection susceptibility is a recessive trait. The availability of this model will allow us to investigate the immunology, genetics, and histopathologic features of bacterial infection of the prostate.

Quantitative trait Loci for glomerulosclerosis, kidney weight and body weight in the focal glomerulosclerosis mouse model

In 183 male progeny derived from a backcross between the FGS/Kist strain, a new mouse model for focal glomerulosclerosis (FGS) in humans, and the standard normal strain, C57BL/6J, we performed a genome-wide scan for quantitative trait loci (QTLs) affecting the glomerulosclerosis index (GSI) based on histological observation as well as kidney and body weights. Two QTLs for GSI (Gsi1-2) located on chromosomes (Chrs) 8 and 10, a kidney weight QTL (Kdw1) on Chr 19, and a body weight QTL (Bdw1) on Chr 13 were detected at the genome-wide 5% or less level. The allele derived from FGS/Kist increased GSI at Gsi1, but decreased it at Gsi2. The mice homozygous for the FGS/Kist allele decreased body and kidney weights. The identified QTLs accounted for 5-8% of the phenotypic variance.

Variants in the Wilms' tumor gene are associated with focal segmental glomerulosclerosis in the African American population

Wilms' tumor gene (WT1) is important for nephrogenesis and gonadal growth. WT1 mutations cause Denys-Drash and Frasier syndromes, which are characterized by glomerular scarring. To test whether genetic variations in WT1 and WIT1 (gene immediately 5' to WT1) associate with focal segmental glomerulosclerosis (FSGS), patients with biopsy-proven idiopathic and HIV-1-associated FSGS were enrolled in a multicenter study. We genotyped SNP rs6508 located in WIT1 exon 1, three SNPs (rs2301250, rs2301252, rs2301254) in the promoter shared by WT1 and WIT1, rs2234590 in exon 6, rs2234591 in intron 6, rs16754 in exon 7, and rs1799937 in intron 9 of WT1. Cases (n = 218) and controls (n = 281) were compared in the African American population. Stratification by HIV-1 infection status showed that SNPs rs6508, rs2301254, and rs1799937 were significantly associated with FSGS [rs6508 odds ratio (OR) 1.82, P = 0.006; rs2301254 OR 1.65, P = 0.049; rs1799937 OR 1.91, P = 0.005] in the non-HIV-1 group and rs2234591 (OR 0.234, P = 0.011) in the HIV-1 group. Haplotype analyses in the population revealed that seven SNPs were associated with FSGS; five SNPs had the highest contingency score [-log10(P value) = 13.57] in the HIV-1 group. This association could not be explained by population substructure. We conclude that SNPs in WT1 and WIT1 genes are significantly associated with FSGS, suggesting that variants in these genes may mediate pathogenesis by altering WT1 function. Furthermore, HIV-1 infection status interacts with genetic variations in both genes to influence this phenotype. We speculate that nephropathy liability alleles in WT1 pathway genes cause podocyte dysfunction and glomerular scarring.

Expression of nephrin in acquired forms of nephrotic syndrome in childhood

Nephrin is a podocyte adhesion molecule located at the slit diaphragm between adjacent glomerular epithelial cells. Mutations in the gene encoding nephrin result in the absence of nephrin or alterations in nephrin causing massive proteinuria in patients with congenital nephrotic syndrome. Given the importance of nephrin to the structural integrity of the glomerular filtration barrier, we postulated that it might also be altered in acquired forms of nephrotic syndrome (NS). To test this hypothesis, frozen kidney biopsy sections from 29 pediatric patients with acquired NS and 5 controls were examined for expression of nephrin. The pathological diagnoses were minimal change disease (MCNS) (19) and focal segmental glomerulosclerosis (FSGS) (10). To determine if nephrin expression differed between children and adults with NS, 10 adult patients and 3 controls were also examined. Nephrin expression was evaluated by immunoperoxidase staining with a monoclonal antibody against the extracellular FnIII portion of human nephrin. In all cases, nephrin expression was seen along the glomerular basement membrane in a finely granular/linear pattern. Expression of nephrin was similar to controls in all 19 patients with MCNS and all 10 patients with FSGS. Areas of sclerosis in patients with FSGS did not demonstrate nephrin expression. A distinctly granular pattern to nephrin expression was seen in adult patients with NS as well as controls. These findings suggest that an alteration in nephrin expression is not a feature of acquired forms of NS in childhood.

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.

Pathobiochemistry of nephrotic syndrome

Nephrotic syndrome is a clinical and laboratory syndrome caused by the increased permeability of the glomerular capillary wall for macromolecules. Nephrotic syndrome is a potentially life-threatening state and persistent nephrotic syndrome has a poor prognosis with a high risk of progression to end-stage renal failure and a high risk of cardiovascular complications due to severe hyperlipidemia. Pathogenesis of increased glomerular permeability in different glomerular diseases has not been fully elucidated. Recently, identification of the mutated genes for some podocyte proteins (nephrin, podocin, alpha-actinin-4) in rare familial forms of nephrotic syndrome shed has new light on the molecular mechanisms of glomerular permselectivity. Gradually it becomes apparent that sporadic mutations of podocyte proteins (e.g., podocin) may be present even in some patients with acquired nephrotic syndrome. Expression of other podocyte proteins may change during the course of experimental nephrotic syndrome, possibly as a response to podocyte damage resulting either in apoptosis or stimulation of proliferation and some form of repair, including glomerular sclerosis. Better understanding of these mechanisms could clearly also have therapeutic implications. Glomerular permeability factors are believed to play a role in some noninflammatory glomerular diseases, mainly minimal change disease and focal segmental glomerulosclerosis, but their molecular identification remains elusive, possibly due to the nonhomogeneous nature of the underlying diseases. As an example, focal segmental glomerulosclerosis possibly can be caused by the sporadic mutation of some genes for podocyte proteins, increased production of glomerular permeability factor (possibly by T lymphocytes), or the loss of inhibitors of glomerular permeability factors in nephrotic urine. Clearly the factors causing increased glomerular permeability and factors perpetuating glomerular sclerosis are not necessarily the same. Proteinuria does not seem to be only the consequence of glomerular damage, but it may possibly cause tubular damage and initiate interstitial fibrosis and thus contribute to the progression of chronic renal failure in proteinuric renal diseases. Recent insights into the mechanisms of tubular protein reabsorption may give new tools for preventing the progression of chronic renal disease. Cubilin inhibitors could potentially ameliorate tubular and interstitial damage in patients with heavy proteinuria refractory to treatment. Nephrotic hyperlipidemia is accompanied with increased risk of cardiovascular complications and should be treated in all patients with persistent nephrotic syndrome. The putative positive effect of hypolipidemic drugs (namely statins) on the cardiovascular risk and potentially also on the rate of progression of chronic renal failure remains to be demonstrated in prospective controlled studies. Recent progress in understanding podocyte biology in rare inherited glomerular diseases gives the chance to understand in the near future the molecular pathogenesis of increased glomerular permeability in the much more common acquired forms of nephrotic syndrome.

Podocyte differentiation and hereditary proteinuria/nephrotic syndromes

The study of familial nephrotic syndromes (NS) and the analysis of murine models of glomerular diseases resulted in major progresses in the knowledge of podocyte physiology and pathology. Numerous proteins participating in the composition of the slit diaphragm region have been identified. The importance of several of them (nephrin, podocin, CD2AP, and Neph1) in the maintenance of the glomerular filtration barrier has been demonstrated by the occurrence of massive proteinuria when they are defective. The role of the cytoskeleton has been revealed by the development of proteinuria/NS in patients with ACTN4 mutation and the occurrence of early and severe NS in alpha-actinin-4-deficient mice. Given the genetic heterogeneity of familial NS and the many other genes to be identified, further insights in the molecular basis of the role of the podocyte in the maintenance of the glomerular filtration barrier may be expected in the near future.

Clinical, histopathologic, and genetic studies in nine families with focal segmental glomerulosclerosis

BACKGROUND

Familial forms of focal segmental glomerulosclerosis (FSGS) are caused by mutations in genes at 1q25-31 (gene for steroid-resistant nephrotic syndrome 2 [NPHS2]), 11q21-22, 19q13 (gene for alpha-actinin 4 and NPHS1), and at additional unidentified chromosomal loci.

METHODS

We describe clinical and histopathologic features and results of linkage analysis in nine consecutive index cases with familial FSGS who, together with their families, were referred for genetic studies.

RESULTS

Two of the index cases presented in childhood (22%) and seven cases presented in adolescence or adulthood (78%). Six of their families (67%), including the two cases with childhood-onset disease, showed probable autosomal recessive inheritance. FSGS segregated at the 1q25-31 locus in two of these families and at the 11q21-22 locus in four families. None had disease caused by mutations in genes at the 19q13 locus, and no locus was identified in the three remaining families. Clinical features of proteinuria, minimal hematuria, hypertension, preeclampsia, and progressive renal impairment were usually present with autosomal recessive or dominant inheritance and with disease that segregated at the different loci. Eighteen renal biopsies from affected members of eight families showed a strong correlation between tubulointerstitial damage and percentage of obsolescent glomeruli (rho = +0.76; P < 0.01). None of the 13 patients from eight families who underwent transplantation developed recurrent FSGS in their grafts. In general, carriers of autosomal recessive disease had no distinctive clinical features apart from the development of preeclampsia in successive pregnancies.

CONCLUSION

Familial forms of FSGS are not uncommon, and presentation frequently is in adolescence or adulthood, even when inheritance is autosomal recessive. Furthermore, carriers of autosomal recessive FSGS often have no distinctive phenotype.

NPHS2 mutations in late-onset focal segmental glomerulosclerosis: R229Q is a common disease-associated allele

Mutations in NPHS2, encoding podocin, have been identified in childhood onset focal and segmental glomerulosclerosis (FSGS). The role of NPHS2 in adult disease is less well defined. We studied 30 families with FSGS and apparent autosomal recessive inheritance and 91 individuals with primary FSGS. We screened family members for NPHS2 mutations. NPHS2 mutations appeared to be responsible for disease in nine of these families. In six families, the affected individuals were compound heterozygotes for a nonconservative R229Q amino acid substitution. This R229Q variant has an allele frequency of 3.6% in a control population. In these families, R229Q was the only mutation identified on one of the two disease-associated NPHS2 alleles. We used in vitro-translated podocin and purified nephrin to investigate the effect of R229Q on their interaction and found decreased nephrin binding to the R229Q podocin. These data suggest that this common polymorphism contributes to the development of FSGS. Chromosomes bearing the R229Q mutation share a common haplotype defining an approximately 0.2-Mb region. R229Q appears to enhance susceptibility to FSGS in association with a second mutant NPHS2 allele. Identification of R229Q mutations may be of clinical importance, as NPHS2-associated disease appears to define a subgroup of FSGS patients unresponsive to corticosteroids.

Linkage heterogeneity of end-stage renal disease on human chromosome 10

BACKGROUND

The human syntenic region of the rodent renal failure-1 gene (Rf1), an attractive candidate region for end-stage renal disease (ESRD) susceptibility, is located on chromosome 10q24-q26. In an attempt to assess for linkage between markers on human chromosome 10 and ESRD, we performed a linkage analysis in 356 African American sib pairs concordant for ESRD [199 sib pairs concordant for non-diabetic etiologies (hypertension-associated, chronic glomerulonephritis and unknown) and 157 sib pairs concordant for diabetic ESRD].

METHODS

Linkage was tested between 30 polymorphic markers spanning chromosome 10 and ESRD using GeneHunter software.

RESULTS

In all 356 sib pairs, the maximum likelihood ratio z-score (Zlr) occurred near locus D10S677 (Zlr = 3.33, P = 0.0004, lod = 3.40), with a lesser peak near D10S1435 (Zlr = 1.77, P = 0.04, lod = 1.42). The locus at D10S677 contributed significantly to both diabetic ESRD (Zlr = 2.39, P = 0.008, lod = 2.08) and non-diabetic ESRD (Zlr = 2.35, P = 0.009, lod = 2.03). Additionally, the D10S677 peak was observed in both early onset (< or =50 years) and late onset (>50 years) ESRD (Zlr = 2.96, P = 0.002, lod = 2.82 in early onset and Zlr = 1.96, P = 0.03, lod = 1.60 in late onset ESRD families, respectively). The lesser peak at D10S1435 was observed in families with non-diabetic etiologies of ESRD (Zlr = 1.94, P = 0.02, lod = 1.58) and in those with early onset ESRD (Zlr = 1.89, P = 0.03, lod = 1.53).

CONCLUSIONS

These results suggest that the region near D10S677, adjacent to the human homolog of the Rf1 gene, contributes to ESRD susceptibility in African Americans. They confirm that the region on 10p, near D10S1435, appears to be involved in early onset, non-diabetic etiologies of ESRD in African Americans.

Proteinuria and glomerulosclerosis in the Sabra genetic rat model of salt susceptibility

In search of an experimental model that would simulate the association between proteinuria and salt sensitivity in humans, we studied protein excretion in the Sabra rat model of salt susceptibility. Monthly measurements of urinary protein excretion in animals fed standard rat chow revealed that normotensive salt-sensitive SBH/y developed proteinuria that averaged 65 +/- 7 mg/day (n = 10) at 9 mo, whereas proteinuria in normotensive salt-resistant SBN/y was 39 +/- 4 mg/day (n = 10) (P < 0.01). Histopathological evaluation revealed focal and segmental glomerulosclerosis (FSGS) lesions grade 2 in SBH/y and normal histology in SBN/y. To amplify the differences between the strains, uninephrectomy was performed. At 9 mo, proteinuria in SBH/y with one kidney (SBH/y-1K) was 195 +/- 12 mg/day (n = 10) and in SBN/y was 128 +/- 10 mg/day (n = 10) (P < 0.001); histopathology revealed FSGS grade 3 in SBH/y-1K and grade 1-2 in SBN/y-1K. To determine the effect of salt loading, animals were provided with 8% NaCl in chow, causing hypertension in SBH/y but not in SBN/y. Proteinuria markedly increased in both SBH/y with two kidneys (SBH/y-2K) and SBH/y-1K, but not in SBN/y; histopathology revealed FSGS grade 1-2 in SBH/y-2K, grade 2 in SBH/y-1K, no lesions in SBN/y-2K, and grade 0-1 in SBN/y-1K. We concluded that the SBH/y strain is more susceptible to develop proteinuria and glomerulosclerosis than SBN/y. In search for the genetic basis of this phenomenon, we investigated the role of candidate proteinuric gene loci. Consomic strains were constructed by introgressing chromosome 1 (which harbors the rf-1 and rf-2 proteinuric loci) or chromosome 17 (which harbors rf-5) from SBH/y onto the SBN/y genomic background. The resulting consomic strains developed marked proteinuria that was severalfold higher than in SBN/y-1K; histopathological evaluation, however, revealed FSGS lesions grade 1-2, similar to those found in SBN/y-1K and less severe than in SBH/y-1K. These results suggest a functional role of gene systems located on chromosomes 1 and 17 in inducing proteinuria in the salt-susceptible Sabra rat strain. These genetic loci do not appear to harbor major genes for glomerulosclerosis.

X Chromosomal short tandem repeat polymorphisms near the phosphoglycerate kinase gene in men with chronic prostatitis

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) causes substantial morbidity afflicting approximately 10% of adult males. Treatment is often empirical and ineffective since the etiology is unknown. Other prostate and genitourinary diseases have genetic components suggesting that CP/CPPS may also be influenced by genetic predisposition. We recently reported a highly polymorphic short tandem repeat (STR) locus near the phosphoglycerate kinase gene within Xq11-13. Because this STR is in a region known to predispose towards other prostate diseases, we compared STR polymorphisms in 120 CP/CPPS patients and 300 control blood donors. Nine distinct allele sizes were detected, ranging from 8 to 15 repeats of the tetrameric STR plus a mutant allele (9.5) with a six base deletion in the flanking DNA sequence. The overall allele size distribution in the CP/CPPS patients differed from controls (Chi-square=19.252, df=8, P=0.0231). Frequencies of two specific alleles, 9.5 and 15, differed significantly in CP/CPPS vs. control subjects and allele 10 differed with marginal significance. Alleles 9.5 and 10 were both more common in CP/CPPS patients than controls while allele 15 was less common. These observations suggest that Xq11-13 may contain one or more genetic loci that predispose toward CP/CPPS. Further investigations involving family studies, larger patient populations, and other control groups may help elucidate this potential genetic predisposition in CP/CPPS.

Approaches to understanding susceptibility to nephropathy: from genetics to genomics

The incidence of end-stage renal disease (ESRD) is increasing worldwide despite efforts to slow the progression of chronic renal failure (CRF) by controlling blood pressure and hyperglycemia. Two available therapies for ESRD, dialysis and transplantation, are expensive and are at best palliative. Recently, data from several laboratories have demonstrated that ESRD is under substantial genetic control, and efforts to identify these genetic determinants are underway. Identifying genes for ESRD pathogenesis has several goals. First, understanding the genetic basis of ESRD offers a means to clarify the mechanisms that result in kidney pathobiology. Second, better and new treatments for prevention of progression of CRF to ESRD may be developed. Third, individuals at risk could be identified early in their course and targeted for intensive therapy. Finally, the products of genes causing disease become target molecules for gene therapy. In this article, we discuss data from our laboratories, which employ two different molecular genetic strategies for identifying ESRD pathogenesis genes. In contrast to traditional experimental design, both approaches are hypothesis generating, identifying candidate molecules for further study, rather than hypothesis driven and may provide novel insights into mechanisms of renal disease progression.

Hemicentin, a conserved extracellular member of the immunoglobulin superfamily, organizes epithelial and other cell attachments into oriented line-shaped junctions

him-4 mutations cause a novel syndrome of tissue fragility, defective cell migration and chromosome instability in Caenorhabditis elegans. Null mutants have abnormal escape reflex, mispositioning of the vas deferens and uterus, and mitotic chromosome loss and multinucleate cells in the germline. The him-4 gene product, hemicentin, is a conserved extracellular matrix protein with 48 tandem immunoglobulin repeats flanked by novel terminal domains. Secreted from skeletal muscle and gonadal leader cells, hemicentin assembles into fine tracks at specific sites, where it contracts broad regions of cell contact into oriented linear junctions. Some tracks organize hemidesmosomes in the overlying epidermis. Hemicentin tracks facilitate mechanosensory neuron anchorage to the epidermis, gliding of the developing gonad along epithelial basement membranes and germline cellularization.

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.