Guanidino compound levels in blood, cerebrospinal fluid, and post-mortem brain material of patients with argininemia.

The paucity of hyperammonemic crises together with spasticity, only seen in human arginase I deficient patients and not in patients with other urea cycle disorders, forces a search for candidates other than ammonia to associate with the pathophysiology and symptomatology. Therefore, we determined arginine together with some catabolites of arginine in blood and cerebrospinal fluid of these patients as well as in extremely rare post-mortem brain material of two patients with argininemia. The levels of alpha-keto-delta-guanidinovaleric acid, argininic acid and alpha-N-acetylarginine correlate with the arginine levels in blood and cerebrospinal fluid of patients with imposed or spontaneous protein restriction. The levels in blood are higher than the upper limit of normal in all studied patients. In addition to the highly increased levels of these same compounds in blood of a child with argininemia, the increase of guanidinoacetic acid, 24h before death, is remarkable. However, the manifest increases of these studied catabolites of arginine are not seen in post-mortem brain material of the same pediatric patient. Otherwise a clear increase of guanidinoacetic acid in post-mortem brain material of an adult patient was shown. A similar, comparable increase of homoarginine in both studied post-mortem brain materials is observed. Therefore the study of the pathobiochemistry of arginine in argininemia must be completed in the future by the determination of the end catabolites of the nitric oxide and agmatine biosynthesis pathways in the knockouts as well as in the patients to evaluate their role, together with the here studied catabolites, as candidates for association with pathophysiology and symptomatology.

Medullary cystic kidney disease type 1: mutational analysis in 37 genes based on haplotype sharing.

Medullary cystic kidney disease type 1 (MCKD1) is an autosomal dominant, tubulo-interstitial nephropathy that causes renal salt wasting and end-stage renal failure in the fourth to seventh decade of life. MCKD1 was localized to chromosome 1q21. We demonstrated haplotype sharing and confirmed the telomeric border by a recombination of D1S2624 in a Belgian kindred. Since the causative gene has been elusive, high resolution haplotype analysis was performed in 16 kindreds. Clinical data and blood samples of 257 individuals (including 75 affected individuals) from 26 different kindreds were collected. Within the defined critical region mutational analysis of 37 genes (374 exons) in 23 MCKD1 patients was performed. In addition, for nine kindreds RT-PCR analysis for the sequenced genes was done to screen for mutations activating cryptic splice sites. We found consistency with the haplotype sharing hypothesis in an additional nine kindreds, detecting three different haplotype subsets shared within a region of 1.19 Mb. Mutational analysis of all 37 positional candidate genes revealed sequence variations in 3 different genes, AK000210, CCT3, and SCAMP3, that were segregating in each affected kindred and were not found in 96 healthy individuals, indicating, that a single responsible gene causing MCKD1 remains elusive. This may point to involvement of different genes within the MCKD1 critical region.

Clinical and genetic evaluation of familial steroid-responsive nephrotic syndrome in childhood.

Steroid-responsive idiopathic nephrotic syndrome (SSINS) is the most common form of nephrotic syndrome in childhood. This article reports a cohort of familial SSINS with disease onset in childhood. The clinical course in terms of age at onset, symptoms during the initial phase, renal morphology, and outcome was evaluated. Furthermore, linkage to NPHS2, the gene for autosomal-recessive steroid-resistant INS on chromosome 1, was examined. Two families with haplotypes consistent with linkage to NPHS2 were evaluated for mutations in the NPHS2 gene. Familial SSINS (32 patients from 15 families, minimal change NS in 12 of 12 biopsies) was found to be a clinically homogeneous entity. Interfamilial and intrafamilial variability with respect to the age at disease onset was low, indicating a strong genetic influence on disease onset. By linkage studies and mutational analysis, familial SSINS was found to be genetically distinct from NPHS2. This is the first report of a large cohort of familial SSINS. Exclusion of linkage to NPHS2 makes likely the existence of a distinct gene locus for SSINS.

Novel mutations in NPHS2 detected in both familial and sporadic steroid-resistant nephrotic syndrome.

Autosomal recessive steroid-resistant nephrotic syndrome (SRINS) belongs to the heterogeneous group of familial nephrotic syndrome and represents a frequent cause of end-stage renal disease in childhood. This kidney disorder is characterized by early onset of proteinuria, progression to end-stage renal disease, and histologic findings of focal segmental glomerulosclerosis, minimal change nephrotic syndrome, or both. A causative gene, NPHS2, has been mapped to chromosome 1q25-q31 and was recently identified by positional cloning. This study reports five novel NPHS2 mutations: A284V, R196P, V290M, IVS4-1G-->T, and 460-467insT in 12 (46%) of 26 multiplex families and in 7 (28%) of 25 single patients with the clinical diagnosis of a SRINS. Because NPHS2 mutations were found in nearly 30% of these patients with "sporadic" SRINS, mutational analysis should also be performed in these patients. Besides better classification of the disease entity, identification of NPHS2 mutations may save some of these patients from unnecessary steroid treatment and also permit the prediction of absence of disease recurrence after kidney transplantation.

No evidence for genotype/phenotype correlation in NPHS1 and NPHS2 mutations.

Primary steroid-resistant nephrotic syndrome (SRNS) is characterized by childhood onset of proteinuria and progression to end-stage renal disease. In 26% of cases it is caused by recessive mutations in NPHS2 (podocin). Congenital nephrotic syndrome (CNS) is caused by mutations in NPHS1 (nephrin) or NPHS2. In three families mutations in NPHS1 and NPHS2 had been reported to occur together, and these tri-allelic mutations were implicated in genotype/phenotype correlations. To further test the hypothesis of tri-allelism, we examined a group of 62 unrelated patients for NPHS1 mutations, who were previously shown to have NPHS2 mutations; 15 of 62 patients had CNS. In addition, 12 CNS patients without NPHS2 mutation were examined for NPHS1 mutations. Mutational analysis yielded three different groups. (1) In 48 patients with two recessive NPHS2 mutations (11 with CNS), no NPHS1 mutation was detected, except for 1 patient, who had one NPHS1 mutation only. This patient was indistinguishable clinically and did not have CNS. (2) In 14 patients with one NPHS2 mutation only (4 with CNS), we detected two additional recessive NPHS1 mutations in the 4 patients with CNS. They all carried the R229Q variant of NPHS2. The CNS phenotype may be sufficiently explained by the presence of two NPHS1 mutations. (3) In 12 patients without NPHS2 mutation (all with CNS), we detected two recessive NPHS1 mutations in 11 patients, explaining their CNS phenotype. We report ten novel mutations in the nephrin gene. Our data do not suggest any genotype/phenotype correlation in the 5 patients with mutations in both the NPHS1 and the NPHS2 genes.

Identification of the first gene locus (SSNS1) for steroid-sensitive nephrotic syndrome on chromosome 2p.

Disease mechanisms of steroid-sensitive nephrotic syndrome (SSNS) remain unknown. Whereas gene identification has furthered the understanding of pathomechanisms in steroid-resistant nephrotic syndrome (SRNS), not even a gene locus is known for SSNS. Total genome linkage analysis was performed in a consanguineous SSNS kindred to identify a gene locus for SSNS. Homozygosity mapping identified a locus for SSNS on chromosome 2p12-p13.2 between markers D2S292 and D2S289 (multipoint LOD score Z(max) = 3.01 at D2S145). The first gene locus for SSNS, as a first step to detect the responsible gene, was thus identified. There was clear evidence for genetic locus heterogeneity upon examination of ten additional families with SSNS.

Familial juvenile hyperuricemic nephropathy and autosomal dominant medullary cystic kidney disease type 2: two facets of the same disease?

Familial juvenile hyperuricemic nephropathy (FJHN) is an autosomal dominant disorder heralded by hyperuricemia during childhood; it is characterized by chronic interstitial nephritis, with marked thickening of tubular basement membranes, and leads to progressive renal failure during adulthood. A gene for FJHN in two Czech families was recently mapped to chromosome 16p11.2, close to the MCKD2 locus, which is responsible for a variant of autosomal dominant medullary cystic kidney disease observed in an Italian family. In a large Belgian family with FJHN, a tight linkage between the disorder and the marker D16S3060, located within the MCKD2 locus on chromosome 16p12 (maximal two-point logarithmic odds score of 3.74 at a recombination fraction of theta = 0), was observed in this study. The candidate region was further narrowed to a 1.3-Mb interval between D16S501 and D16S3036. Together with the striking clinical and pathologic resemblance between previously reported medullary cystic kidney disease type 2 and FJHN occurring in the Belgian family (including the presence of medullary cysts), this study suggests that these two disorders are facets of the same disease.

Mutations of the Uromodulin gene in MCKD type 2 patients cluster in exon 4, which encodes three EGF-like domains.

BACKGROUND: Autosomal-dominant medullary cystic kidney disease type 2 (MCKD2) is a tubulointerstitial nephropathy that causes renal salt wasting, hyperuricemia, gout, and end-stage renal failure in the fifth decade of life. The chromosomal locus for MCKD2 was localized on chromosome 16p12. Within this chromosomal region, Uromodulin (UMOD) was located as a candidate gene. UMOD encodes the Tamm-Horsfall protein. By sequence analysis, one group formerly excluded UMOD as the disease-causing gene. In contrast, recently, another group described mutations in the UMOD gene as responsible for MCKD2 and familial juvenile hyperuricemic nephropathy (FJHN). METHODS: Haplotype analysis for linkage to MCKD2 was performed in 25 MCKD families. In the kindreds showing linkage to the MCKD2 locus on chromosome 16p12, mutational analysis of the UMOD gene was performed by exon polymerase chain reaction (PCR) and direct sequencing. RESULTS: In 19 families, haplotype analysis was compatible with linkage to the MCKD2 locus. All these kindreds were examined for mutations in the UMOD gene. In three different families, three novel heterozygous mutations in the UMOD gene were found and segregated with the phenotype in affected individuals. Mutations were found only in exon 4. CONCLUSION: We confirm the UMOD gene as the disease-causing gene for MCKD2. All three novel mutations were found in the fourth exon of UMOD, in which all mutations except one (this is located in the neighboring exon 5) published so far are located. These data point to a specific role of exon 4 encoded sequence of UMOD in the generation of the MCKD2 renal phenotype.

Refinement of the critical region for MCKD1 by detection of transcontinental haplotype sharing.

BACKGROUND: Autosomal-dominant medullary cystic kidney disease type 1 (MCKD1) [OMIM 174000] is a hereditary nephropathy that leads to renal salt wasting and end-stage renal failure at a median age of 62 years. In a Welsh MCKD1 kindred we have recently demonstrated linkage to the MCKD1 locus on chromosome 1q23.1 and refined the critical MCKD1 region to <3.3 Mb. METHODS: In order to refine the candidate gene region for MCKD1, high-resolution haplotype analysis in three large kindreds with MCKD1 was performed. RESULTS: We report here on high-resolution haplotype analysis in this Welsh kindred, as well as in the Arizona kindred, which was used for the first definition of MCKD as a disease entity, and in a kindred from the Dutch/German border. We detected extensive haplotype sharing among all affected individuals of all three kindreds. Scrutinization of the genealogy of the Arizona kindred revealed an origin from Germany in the 17th century, thereby providing historical data for haplotype sharing by descent at the MCKD1 locus. CONCLUSION: Under the hypothesis of haplotype sharing by descent, we refined the critical genetic interval to <650 kb, thus enabling candidate gene analysis.

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.

Telomeric refinement of the MCKD1 locus on chromosome 1q21.

BACKGROUND: Autosomal-dominant medullary cystic kidney disease type 1 (MCKD1) is a tubulointerstitial nephropathy that causes renal salt wasting and end-stage renal failure in the sixth decade of life. The chromosomal locus for MCKD1 was localized to chromosome 1q21 in a Cyprotic kindred. In this report we describe further refinement of the critical genetic region by a recombination in a Belgian kindred. METHODS: Clinical data and blood samples of 33 individuals from a large Belgian kindred were collected and high-resolution haplotype analysis was performed. RESULTS: In the Belgian kindred linkage to the MCKD1 locus on chromosome 1q21 was found with a logarithm of odds (LOD) score significant for linkage. A recombination in individual III:7 for marker D1S2624 refines the critical genetic region to 2.1 Mb. In this kindred a wide variety of clinical symptoms and age of onset of renal failure was detected. CONCLUSION: We confirm the MCKD1 locus on chromosome 1q21 and show further refinement of the MCKD1 locus to 2.1 Mb. This allowed us to exclude another 17 genes as positional candidate genes.