Nephrocystin-5, a ciliary IQ domain protein, is mutated in Senior-Loken syndrome and interacts with RPGR and calmodulin.

Nephronophthisis (NPHP) is the most frequent genetic cause of chronic renal failure in children. Identification of four genes mutated in NPHP subtypes 1-4 (refs. 4-9) has linked the pathogenesis of NPHP to ciliary functions. Ten percent of affected individuals have retinitis pigmentosa, constituting the renal-retinal Senior-Loken syndrome (SLSN). Here we identify, by positional cloning, mutations in an evolutionarily conserved gene, IQCB1 (also called NPHP5), as the most frequent cause of SLSN. IQCB1 encodes an IQ-domain protein, nephrocystin-5. All individuals with IQCB1 mutations have retinitis pigmentosa. Hence, we examined the interaction of nephrocystin-5 with RPGR (retinitis pigmentosa GTPase regulator), which is expressed in photoreceptor cilia and associated with 10-20% of retinitis pigmentosa. We show that nephrocystin-5, RPGR and calmodulin can be coimmunoprecipitated from retinal extracts, and that these proteins localize to connecting cilia of photoreceptors and to primary cilia of renal epithelial cells. Our studies emphasize the central role of ciliary dysfunction in the pathogenesis of SLSN.

Pseudodominant inheritance of nephronophthisis caused by a homozygous NPHP1 deletion.

Nephronophthisis (NPHP) is an autosomal recessive kidney disease characterized by tubular basement membrane disruption, interstitial infiltration, and tubular cysts. NPHP leads to end-stage renal failure (ESRD) in the first three decades of life and is the most frequent genetic cause of chronic renal failure in children and young adults. Extrarenal manifestations are known, such as retinitis pigmentosa, brainstem and cerebellar anomalies, liver fibrosis, and ocular motor apraxia type Cogan. We report on a Turkish family with clinical signs of nephronophthisis. The phenotype occurred in two generations and therefore seemed to be inherited in an autosomal dominant pattern. Nevertheless, a deletion analysis of the NPHP1 gene on chromosome 2 was performed and showed a homozygous deletion. Analysis of the family pedigree indicated no obvious consanguinity in the last three generations. However, haplotype analysis demonstrated homozygosity on chromosome 2 indicating a common ancestor to the parents of all affected individuals. NPHP1 deletion analysis should always be considered in patients with apparently dominant nephronophthisis. Furthermore, three out of four patients developed ESRD between 27 and 43 years of age, which may be influenced by yet unknown modifier genes.

Prevalence of Capsular Serotype, Pilus Island Distribution, and Antibiotic Resistance in Pediatric and Adult Invasive Group B Streptococcus Isolates: Data From a Nationwide Prospective Surveillance Study in Germany.

For neonates, group B Streptococcus is life threatening. Current prevention strategies remain insufficient, especially for cases of late-onset sepsis, where intrapartum antibiotic prophylaxis has demonstrated no benefit. One promising approach is the vaccination of pregnant women, which offers protective immunity via transplacental transmission of neutralizing antibodies. Our nationwide, prospective surveillance study aimed to characterize the prevalence of pilus antigen, capsular polysaccharide serotypes, and antibiotic resistance from invasive GBS infections in neonates and compare these results with those from children and adults in Germany. Our study includes 173 neonatal isolates of a total of 450 reported cases during the study period (incidence: 0.34/1000 live births), in addition to 2 pediatric and 803 adult isolates. The comparison between neonatal and adult isolates reveals age-dependent differences in capsular serotype and pilus type distribution and differences in antibiotic resistance patterns.

Mutational analysis of the NPHP4 gene in 250 patients with nephronophthisis.

Nephronophthisis (NPH), a recessive cystic kidney disease, is the most frequent genetic cause for end-stage renal disease in the first two decades of life. Mutations in three genes (NPHP1, 2, and 3) were identified as causative. Extrarenal manifestations are known, such as retinitis pigmentosa (Senior-Loken syndrome, SLS) and ocular motor apraxia type Cogan. Recently, we identified a novel gene (NPHP4) as mutated in NPH. To date, a total of only 13 different NPHP4 mutations have been described. To determine the frequency of NPHP4 mutations, we performed mutational analysis by direct sequencing of all 30 NPHP4 exons in 250 different patients with isolated NPH, SLS, or Cogan syndrome ascertained worldwide over 14 years. We identified 23 novel NPHP4 sequence variants in 26/250 different patients (10%). Interestingly, we detected homozygous or compound heterozygous mutations of NPHP4 in only 6/250 different patients (2.4%), but only one heterozygous NPHP4 sequence variant in 20/250 different patients (8%). In the six patients with two NPHP4 mutations, 5/8 mutations (63%) were likely loss-of-function mutations, whereas in the 20 patients with only one sequence variant, only 1/20 (5%) was a likely loss-of-function (i.e., truncating) mutation. We conclude that: i) two recessive mutations in NPHP4 are a rare cause of nephronophthisis; ii) single heterozygous NPHP4 sequence variants are three times more prevalent than two recessive mutations; iii) there is no genotype/phenotype correlation; iv) there must exist further genes causing nephronophthisis, since in 224/250 (90%) patients, no sequence variants in either of the four NPH genes were detected.

Mapping a new suggestive gene locus for autosomal dominant nephrolithiasis to chromosome 9q33.2-q34.2 by total genome search for linkage.

BACKGROUND: Nephrolithiasis is a complex, multifactorial disease resulting from genetic and environmental interaction. The pathogenesis of nephrolithiasis is far from being understood. So far, no gene locus for autosomal dominant nephrolithiasis only has been described. We here identified a new suggestive gene locus for autosomal dominant nephrolithiasis by a genome-wide search for linkage in a Spanish kindred with nephrolithiasis. METHODS: Clinical data, blood and urine samples of 18 individuals from a Spanish kindred with nephrolithiasis were collected. We performed a genome-wide search for linkage using 380 polymorphic microsatellite markers. RESULTS: Nephrolithiasis segregated in this Spanish kindred in a pattern compatible with autosomal dominant inheritance. The total genome search yielded the highest two-point LOD score of Z(max) = 1.99 (theta = 0) for marker D9S159 on chromosome 9q33.2-q34.2. Multipoint analysis of 24 polymorphic markers used for further fine mapping resulted in a LOD score of Z(max) = 2.7 (theta = 0) for markers D9S1881-D9S164, thereby identifying a new gene locus for autosomal dominant nephrolithiasis (NPL1). Two recombination events define D9S1850 as the centromeric flanking marker and D9S1818 as the telomeric flanking marker, restricting the NPL1 locus to a 14 Mb interval. CONCLUSION: We here identified a new suggestive gene locus (NPL1) for autosomal dominant nephrolithiasis. It is localized on chromosome 9q33.2-q34.2. The identification of the responsible gene will provide new insights into the molecular basis of nephrolithiasis.

Patients with mutations in NPHS2 (podocin) do not respond to standard steroid treatment of nephrotic syndrome.

Nephrotic syndrome (NS) represents the association of proteinuria, hypoalbuminemia, edema, and hyperlipidemia. Steroid-resistant NS (SRNS) is defined by primary resistance to standard steroid therapy. It remains one of the most intractable causes of ESRD in the first two decades of life. Mutations in the NPHS2 gene represent a frequent cause of SRNS, occurring in approximately 20 to 30% of sporadic cases of SRNS. On the basis of a very small number of patients, it was suspected that children with homozygous or compound heterozygous mutations in NPHS2 might exhibit primary steroid resistance and a decreased risk of FSGS recurrence after kidney transplantation. To test this hypothesis, NPHS2 mutational analysis was performed with direct sequencing for 190 patients with SRNS from 165 different families and, as a control sample, 124 patients with steroid-sensitive NS from 120 families. Homozygous or compound heterozygous mutations in NPHS2 were detected for 43 of 165 SRNS families (26%). Conversely, no homozygous or compound heterozygous mutations in NPHS2 were observed for the 120 steroid-sensitive NS families. Recurrence of FSGS in a renal transplant was noted for seven of 20 patients with SRNS (35%) without NPHS2 mutations, whereas it occurred for only two of 24 patients with SRNS (8%) with homozygous or compound heterozygous mutations in NPHS2. None of 29 patients with homozygous or compound heterozygous mutations in NPHS2 who were treated with cyclosporine A or cyclophosphamide demonstrated complete remission of NS. It was concluded that patients with SRNS with homozygous or compound heterozygous mutations in NPHS2 do not respond to standard steroid treatment and have a reduced risk for recurrence of FSGS in a renal transplant. Because these findings might affect the treatment plan for childhood SRNS, it might be advisable to perform mutational analysis of NPHS2, if the patient consents, in parallel with the start of the first course of standard steroid therapy.

A gene locus for steroid-resistant nephrotic syndrome with deafness maps to chromosome 14q24.2.

Steroid-resistant nephrotic syndrome (SRNS) leads to end-stage renal disease (ESRD) in childhood or young adulthood. Positional cloning for genes causing SRNS has opened the first insights into the understanding of its pathogenesis. This study reports a genome-wide search for linkage in a consanguineous Palestinian kindred with SRNS and deafness and detection of a region of homozygosity on chromosome 14q24.2. Multipoint analysis of 12 markers used for further fine mapping resulted in a LOD score Z(max) of 4.12 (theta = 0) for marker D14S1025 and a two-point LOD score of Z(max) = 3.46 (theta = 0) for marker D14S77. Lack of homozygosity defined D14S1065 and D14S273 as flanking markers to a 10.7 cM interval. The identification of the responsible gene will provide new insights into the molecular basis of nephrotic syndrome and sensorineural deafness.

Prevalence of WT1 mutations in a large cohort of patients with steroid-resistant and steroid-sensitive nephrotic syndrome.

BACKGROUND: Nephrotic syndrome (NS) represents the association of proteinuria, hypoalbuminemia, edema, and hyperlipidemia. Steroid-resistant nephrotic syndrome (SRNS) is defined by primary resistance to standard steroid therapy. It remains one of the most intractable causes for end-stage renal disease (ESRD) in the first two decades of life. Sporadic mutations in the Wilms' tumor suppressor gene WT1 have been found to be present in patients with SRNS in association with Wilms' tumor (WT) and urinary or genital malformations, as well as in patients with isolated SRNS. METHODS: To further evaluate the incidence of WT1 mutations in patients with NS we performed mutational analysis in 115 sporadic cases of SRNS and in 110 sporadic cases of steroid-sensitive nephrotic syndrome (SSNS) as a control group. Sixty out of 115 (52%) patients with sporadic SRNS were male, 55/115 (48%) were female. Sex genotype was verified by haplotype analysis. Mutational analysis was performed by direct sequencing and by denaturing high-performance liquid chromatography (DHPLC). RESULTS: Mutations in WT1 were found in 3/60 (5%) male (sex genotype) cases and 5/55 (9%) female (sex genotype) cases of sporadic SRNS, and 0/110 (0%) sporadic cases of SSNS. One out of five female patients with mutations in WT1 developed a WT, 2/3 male patients presented with the association of urinary and genital malformations, 1/3 male patients presented with sexual reversal (female phenotype) and bilateral gonadoblastoma, and 4/5 female patients presented with isolated SRNS. CONCLUSION: According to the data acquired in this study, patients presenting with a female phenotype and SRNS and male patients presenting with genital abnormalities should especially be screened to take advantage of the important genetic information on potential Wilms' tumor risk and differential therapy. This will also help to provide more data on the phenotype/genotype correlation in this patient population.