Novel molecular variants of the Na-K-2Cl cotransporter gene are responsible for antenatal Bartter syndrome

Antenatal Bartter syndrome is a variant of inherited renal-tubular disorders associated with hypokalemic alkalosis. This disorder typically presents as a life-threatening condition beginning in utero, with marked fetal polyuria that leads to polyhydramnios and premature delivery. Another hallmark of this variant is a marked hypercalciuria and, as a secondary consequence, the development of nephrocalcinosis and osteopenia. We have analyzed 15 probands belonging to 13 families and have performed SSCP analysis of the coding sequence and the exon-intron boundaries of the NKCC2 gene; and we report 14 novel mutations in patients with antenatal Bartter syndrome, as well as the identification of three isoforms of human NKCC2 that arise from alternative splicing.

Identification of a novel Ran binding protein 2 related gene (RANBP2L1) and detection of a gene cluster on human chromosome 2q11-q12

The giant 358-kDa protein Ran binding protein 2 (RanBP2/Nup358) is localized at the cytoplasmic side of the nuclear pore complex and likely constitutes the Ran-GTP binding site at the cytoplasmic face of the complex. RanBP2/Nup358 furthermore acts as a chaperone for red/green opsin molecules. Here, we report on the physical mapping of human RanBP2 between markers D2S340 and D2S1893. A duplication of the 5'-end sequence of RanBP2 occurs within 3 Mb distal to RanBP2. Detailed sequence analysis resulted in primers specific for this distal duplication. Polymerase chain reaction-based screening of cDNA libraries indicates that this transcript, called RanBP2alpha (HGMW-approved symbol RANBP2L1), is expressed in several tissues. Screening of a fetal brain cDNA library yielded a 4057-bp partial cDNA clone for RanBP2alpha. Its 5'-end is almost identical to RanBP2, whereas its 3'-part is distinct from RanBP2. Northern blot analysis using a probe of the 3'-untranslated sequence of RanBP2alpha detected in several tissues an 8-kb transcript representing the full length of the transcript. In pancreas and placenta, an additional transcript of 14 kb was detected. PAC clones containing the bona fide RanBP2 sequences were localized to 2q11-q12 by FISH analysis, and a region of high similarity was detected on 2p11-p12. In summary, we have identified a RanBP2 gene cluster on 2q11-q12 together with a novel gene termed RanBP2alpha, with high sequence similarity to RanBP2.

Acute bilateral renal vein thrombosis complicating Netherton syndrome

A 1-year old male infant suffering from Netherton syndrome with severe generalized erythroderma presented with acute renal failure due to bilateral renal vein thrombosis (RVT) after a short episode of enteritis. The imperceptible fluid loss through the skin and the additional enteric water loss had led to decompensation of the delicate fluid balance and had resulted in RVT as a sequel of haemoconcentration. Reperfusion of the left kidney could be achieved by treatment with urokinase and heparin. Prophylactic oral anticoagulation was instituted for several weeks.

CONCLUSION

In severe Netherton disease meticulous surveillance of the fluid balance is important and aggressive treatment is indicated in case of additional fluid loss.

Linkage and allelic association of atopy and markers flanking the IL4-receptor gene

BACKGROUND

Atopy, a clinical syndrome characterized by heightened IgE responsiveness, is largely determined by genetic factors. The disease may well be heterogeneous but the mode of inheritance is unknown. Several genes have been named which affected IgE responsiveness. However, results are conflicting reflecting heterogeneity and a complicated inheritance pattern of the atopic syndrome. In 1994 linkage of the 5q32 gene region and elevated total IgE levels were reported, leaving the IL4 gene as a prominent candidate.

OBJECTIVES

We were interested in a possible involvement of the IL4-receptor gene in the development of atopy.

METHODS

We employed sib-pair linkage analysis using highly polymorphic microsatellite markers within and flanking the IL4 receptor gene in atopic families, characterized for specific sensitization to inhalant allergens and elevated total serum IgE. Allele sizes were determined for all microsatellite probes to allow transmission disequilibrium analysis.

RESULTS

We found significant sharing of maternal but not paternal alleles in affected sibs from two independent populations, both of which presented enhanced IgE responsiveness. Linkage and maternal inheritance could be confirmed by transmission disequilibrium analysis.

CONCLUSIONS

We conclude from our findings that maternal inheritance of a gene in the chromosome 16p12 region increases the risk for enhanced IgE responsiveness. The most prominent candidate in this region is represented by the IL4 receptor gene.

Construction of a gene map of the nephronophthisis type 1 (NPHP1) region on human chromosome 2q12-q13

A gene for the autosomal recessive kidney disorder juvenile nephronophthisis (NPH) is located on chromosome 2q between markers D2S1893 and D2S1888. Recently, the presence of large homozygous deletions was described in the majority of NPH patients. We constructed an integrated YAC/PAC contig of 54 markers and 30 PAC clones that encompasses this deletion and the flanking inverted duplication. Thirty-six novel sequence-tagged site markers were generated for this region of 2-3 Mb, 22 of which represent PAC ends. Ten of 18 multiplex NPH families show a homozygous deletion for 8 consecutive markers. BlastN database search and expressed sequence tag (EST) mapping led to the localization of 18 EST clones to the integrated contig, representing 11 putative transcribed sequences. Seven EST clones were localized to the NPHP1 region between D2S1893 and D2S1888. Two EST clones, zc07a11 from a human parathyroid tumor library and yy63e10 from a multiple sclerosis lesion library, are located in the deletion region. PCR amplification experiments indicate that zc07a11 represents a chimeric cDNA. Through FISH analysis the NPHP1 deletion region was localized to 2q12-q13. In summary, our study provides a high-resolution physical map of the NPHP1 region with 7 precisely localized expressed sequences, 2 of which have recently been shown to be part of a gene for NPH. These data will alleviate the identification of further genes of a homozygous gene deletion syndrome in patients with NPH and oculomotor apraxia and will be instrumental in the characterization of the molecular mechanism leading to the large homozygous deletion in this region. The data furthermore provide an important step toward the construction of a sequence-ready PAC contig of this region.

Lack of large, homozygous deletions of the nephronophthisis 1 region in Joubert syndrome type B. APN Study Group. Arbeitsgemeinschaft für Pädiatrische Nephrologie

Joubert syndrome type B (JSB) is a developmental disorder of the nephronophthisis (NPH) complex with multiple organ involvement, including NPH, coloboma of the eye, aplasia of the cerebellar vermis, and the facultative symptoms of psychomotor retardation, polydactyly, and neonatal tachypnea. In isolated autosomal recessive NPH type 1 (NPH1), homozygous deletions have been described as causative in more than 80% of patients. Since different combinations of the extrarenal symptoms with NPH occur in JSB, a contiguous gene deletion syndrome in the NPH1 genetic region would seem a highly likely cause for JSB. We therefore examined 11 families with JSB for the presence of extended deletions at the NPH1 locus. Genomic DNA was examined using four consecutive polymerase chain reaction (PCR) markers that are deleted in NPH1 and three PCR makers flanking the NPH1 deletion. In all seven markers examined, there was no homozygous deletion detected in any of the 11 JSB families studied. Since these markers saturate the NPH1 deletion region at high density, this finding excludes the presence of large homozygous deletions of the NPH1 region in these JSB families, making it unlikely that deletions of the NPH1 region are a primary cause for JSB.

Two novel mutations of the gene for Kir 1.1 (ROMK) in neonatal Bartter syndrome

Bartter syndrome, an autosomal recessive renal tubular disorder, is associated with hypokalemic metabolic alkalosis with high renin and aldosterone plasma concentrations with low or normal blood pressure and renal salt loss. Two genes, the gene encoding the furosemide-sensitive apical Na-K-2Cl cotransporter (NKCC2) and the gene encoding the luminal inwardly-rectifying potassium channel Kir 1.1 (ROMK), have been reported to cause the neonatal subtype of Bartter syndrome. In a patient with neonatal Bartter syndrome, we report two novel mutations resulting in amino acid exchanges Ala156Val and Leu220Phe in the gene for Kir 1.1 that have been identified by single-strand conformation polymorphism analysis and subsequent direct sequencing. Both mutations occur in functional relevant domains of the channel protein and are therefore highly suggestive of altering channel properties.

A novel gene encoding an SH3 domain protein is mutated in nephronophthisis type 1

Juvenile nephronophthisis (NPH), an autosomal recessive cystic kidney disease, is the primary genetic cause of chronic renal failure in children. About two thirds of patients with NPH carry a large homozygous deletion at the gene locus NPH1 on 2q13. We here identify a novel gene. NPHP1, which extends over most of this common deletion. The 4.5-kb transcript encodes a protein with an SH3 domain, which is highly conserved throughout evolution. The 11-kb interval between the 3' end of NPHP1 and an inverted repeat containing the distal deletion breakpoint was found to contain the first exon of a second gene, MALL. In patients with a hemizygous deletion of the NPH1 region, additional point mutations were found in NPHP1 but not in MALL.

Late occurrence of cysts in autosomal dominant medullary cystic kidney disease

Medullary cystic kidney disease (MCD) is characterized by multiple renal cysts at the corticomedullary boundary area, by autosomal dominant inheritance, and by onset of chronic renal failure in the third decade of life. We report on a family with three affected individuals of both sexes in two generations presenting with end-stage renal failure at age 22-31 years. Primarily diagnoses considered included unclassified hereditary nephropathy and autosomal dominant polycystic kidney disease. Careful evaluation of all findings, initiated after investigation of renal morphology with CT, revealed features characteristic for MCD and led to the final diagnosis of MCD. We conclude that MCD is an important differential diagnosis for polycystic kidney disease in young adults with end-stage renal failure. Establishing the correct diagnosis has considerable impact for genetic counselling.

Molecular cloning of the interleukin-1 gene cluster: construction of an integrated YAC/PAC contig and a partial transcriptional map in the region of chromosome 2q13

Genes of the interleukin-1 (IL-1) gene cluster localized on chromosome 2q13 are implicated in many physiological and pathophysiological processes. We present here a high-resolution physical map of this region between markers D2S2008 and D2S4/PAX8. An integrated YAC/PAC contig and a partial transcriptional map were constructed by STS-constent mapping using the CEPH YAC library and three PAC libraries. A total of 3 YACs, 34 PACs, and 56 STSs were integrated: 33 newly generated probes to PAC end sequences, 9 polymorphic and 4 nonpolymorphic markers, 5 known genes, 4 expressed sequence tags, and 1 pseudogene. Within the map, a complete PAC contig of > 1 Mb encompasses the IL-1 gene cluster and PAX8, a paired-box-containing gene. This allowed us to define the transcriptional orientation of GLVR1, IL1B, and IL1RN and to show that PAX8 is localized outside the IL-1 gene cluster. FISH analysis localized PAC clones containing the IL-1 gene cluster to 2q12-q13. The data provide the basis for further characterization of the IL-1 gene cluster and for the construction of a sequence-ready PAC contig of this region.

Probable Opitz trigonocephaly C syndrome with medulloblastoma

We report on a patient with trigonocephaly, biparietal widening as a result of metopic synostosis, strabismus, upslanted palpebral fissures, apparently low-set ears with abnormal helices, deeply furrowed palate, postaxial polysyndactyly of the feet, ankle flexion deformities, cryptorchidism, loose skin, and severe mental retardation, findings compatible with a diagnosis of the Opitz trigonocephaly C syndrome (OTS). At the age of 12 years this patient presented with symptoms of raised intracranial pressure. A biopsy showed findings diagnostic of a medulloblastoma WHO Grade IV, an unprecedented finding in OTS. The possibility of coincidence should not prevent continued surveillance of OTS patients in the future for the occurrence of malignancy.

Molecular genetic identification of families with juvenile nephronophthisis type 1: rate of progression to renal failure. APN Study Group. Arbeitsgemeinschaft für Pädiatrische Nephrologie

Familial juvenile nephronophthisis (NPH), an autosomal recessive cystic disease of the kidney, is the most common genetic cause of end-stage renal disease (ESRD) in the first two decades of life. A gene locus for nephronophthisis type 1 (NPH1) has been mapped by linkage analysis to chromosome 2q13. We performed a haplotype analysis in 16 NPH families with at least two affected patients with the typical history, clinical signs and histology of NPH using microsatellite markers of the NPH1 genetic region. By demonstration of a recombinant event marker D2S1893 was identified as a novel centromeric flanking marker to the NPH1 critical genetic region. Absence of linkage to the NPH1 locus in six NPH families confirmed the existence of at least one additional gene locus for NPH. Linkage to the NPH1 locus was demonstrated in 10 families. In 8 of these families a homozygous deletion was identified. These data permit for the first time the study of the development of renal failure in a subset of NPH1 families, which is most likely homogeneous with regard to the responsible gene locus. We present a statistical description of serial serum creatinine measurements in NPH1. Analysis of renal death revealed a median of 13.1 years. Age-dependent quartiles were generated for serum creatinine. In summary, the new marker provides a diagnostic tool to aid in the diagnosis of NPH, while the progression charts offer a standard for an assessment of the rate of progression to ESRD for patients with NPH1 to be used in future therapeutic trials and for a prediction of the individual course of the disease.

Familial glomerulopathy with giant fibrillar (fibronectin-positive) deposits: 15-year follow-up in a large kindred

A 15-year clinical follow-up is reported for a familial glomerulopathy characterized on light microscopy by the glomerular deposition of giant fibrillary deposits (Virchows Arch A Pathol Anat Histol 388:313-326, 1980). On electron microscopy, the deposits consist of randomly oriented fibrils (12 to 16 nm in width and 120 to 170 nm in length). These deposits show positive immunoreactivity for fibronectin. One hundred fifty-seven of 197 family members within five generations were investigated. The disease is characterized by the occurrence of albuminuria in the third to fourth decades of life and slow progression to end-stage renal disease over a period of 15 to 20 years with the occurrence of generalized distal tubular acidosis (renal tubular acidosis type IV), hypertension, and the nephrotic syndrome. The frequent occurrence of otherwise unexplained microalbuminuria in young individuals of generations IV and V could be indicative of incipient glomerular disease. In one affected male individual and in his unaffected sister, renal cell carcinoma was diagnosed, raising the possibility that this familial glomerulopathy might be associated with an increased risk to develop renal cell cancer by direct or indirect (associated genetic predisposition) mechanisms. The disease relapsed in one renal transplant, raising the possibility of the presence of a transferable factor that could be part of the deposited fibrillar material or, alternatively, interfere with the glomerular handling of the deposited material.

Glomerulopathy associated with predominant fibronectin deposits: exclusion of the genes for fibronectin, villin and desmin as causative genes

Glomerulopathy with predominant fibronectin deposits (GFD) is a newly recognized autosomal dominant renal disease that leads to albuminuria, microscopic hematuria, hypertension, renal tubular acidosis type IV, and end-stage renal disease in the second to fourth decade of life. Light microscopy documents extensive deposits in the subendothelial space, which on electron microscopy consist of non-oriented 12 x 125 nm fibers. Deposits are strongly immunoreactive for antibodies to fibronectin. We examined the hypothesis that a genetic defect in the gene for fibronectin is responsible for the disease. In a 197 member pedigree, 13 relatives developed end-stage renal failure from the disease. In 99 individuals haplotype analysis was performed using 6 microsatellite markers spanning a > 56 cM interval in chromosome region 2q34, where fibronectin, villin, and desmin map in close proximity. Haplotype analysis resulted in exclusion of the whole range of 78 cM covered by the markers examined. This result excludes fibronectin, villin, and desmin from being the causative genes for GFD in this large kindred.

Physical mapping of the gene for juvenile nephronophthisis (NPH1) by construction of a complete YAC contig of 7 Mb on chromosome 2q13

Familial juvenile nephronophthisis (NPH) is an autosomal recessive cystic disease of the kidney that leads to end-stage renal failure in adolescence. NPH is the most common genetic cause of end-stage renal disease in children. A gene locus for nephronophthisis (NPH1) has been mapped by linkage analysis to chromosome 2q13. We report here the construction of a complete YAC contig in the minimum genetic region for NPH1 by STS content mapping using clones of the CEPH YAC libraries. A physical map of maximum distances between 32 STS markers was constructed, thereby defining the order of a total of 27 STS markers. Since D2S340 and D2S121 have previously been identified as flanking markers to the NPH1 gene, the new contig defines on a physical map the NPH1 minimum genetic region to a 6.4-Mb interval. As a novel assignment, expressed genes, some of which may be candidates for the disease, were localized to the NPH1 region. In addition, the known interstitial telomeric repeat on chromosome 2 was physically mapped to this region. This contig assembly provides the basis for closer definition of the NPH1 critical region through identification of more narrow flanking markers and for the construction of a transcriptional map of the region towards isolation of the NPH1 gene.

Genetic renal diseases in children

In this review, a survey is given of genetic renal diseases in which recent progress has been made regarding the study of their molecular genetics. Diseases in which the responsible gene has been identified are discussed first, followed by a description of diseases in which successful chromosomal mapping has been achieved. The recent progress in this field will lead to advances in the diagnosis and understanding of the pathogenic mechanisms of genetic renal diseases and, potentially, will have implications for therapeutic interventions. The International Studies of Genetic Renal Diseases, which promotes the study of genetic renal disease, has recently provided an international database called kidbase, which is accessible via the Internet.

Refined genetic mapping of a gene for familial juvenile nephronophthisis (NPH1) and physical mapping of linked markers. APN Study Group

We have recently assigned a gene for familial juvenile nephronophthisis (NPH1) to chromosome 2q between microsatellite markers at loci D2S135 and D2S110. Here we have extended and refined our previous linkage analysis by studying five additional NPH families and by testing five additional markers. By haplotype analysis in a large family yielding proof of linkage, D2S135 and D2S283 were defined with certainty as flanking the NPH1 critical region within a 14-cM interval. These data now allow cytogenetic assignment of the NPH1 critical region to 2q11.1-q21.1. Furthermore, haplotype analysis in 12 small families helped to define as flanking markers D2S293 and D2S363, which span an 8-cM interval. Multipoint linkage analysis by the location score method resulted in a maximum multipoint lod score of 10.30. The Zmax-1 support interval spans 6.9 cM and is flanked by marker loci D2S293 and D2S363. Since IL1A maps to this region and has been cytogenetically mapped to 2q13 in the literature, NPH1 can be assigned more closely to 2q13 or adjacent bands. Contigs of CEPH mega-YAC clones in the region were established by screening the clones with microsatellite markers, adding marker IL1A to the physical map as a novel assignment. We conclude that the NPH1 gene most probably localizes to an interval of 6.9 cM between marker loci D2S293 and D2S363 in the vicinity of 2q13. This contig mapping provides the basis for cloning of this interval and for isolation of the NPH1 gene.

Mapping of a gene for familial juvenile nephronophthisis: refining the map and defining flanking markers on chromosome 2. APN Study Group

Familial juvenile nephronophthisis (NPH) is an autosomal recessive kidney disease that leads to end-stage renal failure in adolescence and is associated with the formation of cysts at the cortico-medullary junction of the kidneys. NPH is responsible for about 15% of end-stage renal disease in children, as shown by Kleinknecht and Habib. NPH in combination with autosomal recessive retinitis pigmentosa is known as the Senior-Løken syndrome (SLS) and exhibits renal pathology that is identical to NPH. We had excluded 40% of the human genome from linkage with a disease locus for NPH or SLS when Antignac et al. first demonstrated linkage for an NPH locus on chromosome 2. We present confirmation of linkage of an NPH locus to microsatellite markers on chromosome 2 in nine families with NPH. By linkage analysis with marker AFM262xb5 at locus D2S176, a maximum lod score of 5.05 at a theta max = .03 was obtained. In a large NPH family that yielded at D2S176 a maximum lod score of 2.66 at theta max = .0, markers AFM172xc3 and AFM016yc5, representing loci D2S135 and D2S110, respectively, were identified as flanking markers, thereby defining the interval for an NPH locus to a region of approximately 15 cM. Furthermore, the cytogenetic assignment of the NPH region was specified to 2p12-(2q13 or adjacent bands) by calculation of linkage between these flanking markers and markers with known unique cytogenetic assignment. The refined map may serve as a genetic framework for additional genetic and physical mapping of the region.

LODVIEW: a computer program for the graphical evaluation of lod score results in exclusion mapping of human disease genes

For linkage analysis projects aimed at mapping hereditary disease genes in humans, hundreds of highly polymorphic microsatellite markers which can be typed by PCR (PCR markers) have become available. With this technical improvement, the availability of a technique allowing for transparency in the handling of rapidly generated lod score data is becoming important. We present a computer program LODVIEW for the graphical representation of lod score data. It is designed for the input of lod score data generated with the LINKAGE package or similar programs. LODVIEW consists of 24 preformatted files, one for each chromosome. Each file contains a table for the input of lod score data and a file for the graphical representation of the data, which will show automatically any entry that is made in the respective input table. The program provides the user with published PCR marker information pre-entered into a table and graph at the correct positions corresponding to the genetic distances between markers. The graphical display of LODVIEW allows for the rapid evaluation of lod score results calculated from PCR markers on each chromosome. The following information can be obtained from the graphical display at one glance: (i) Regions of exclusion (Z(theta) < -2) and nonexclusion, (ii) markers with positive lod scores, (iii) the distribution of positive and negative lod scores among the families examined (indication of genetic heterogeneity), (iv) multipoint lod scores, and (v) the availability of PCR markers in regions of interest. The program is continually updated for novel PCR marker information from the literature. The program will help to efficiently monitor and direct the progress of exclusion mapping projects.

A gene for familial juvenile nephronophthisis (recessive medullary cystic kidney disease) maps to chromosome 2p

Familial juvenile nephronophthisis (NPH) is a chronic autosomal recessive kidney disease responsible for 15% of end stage renal failure in children. NPH is frequently (16% of cases) associated with Leber amaurosis (termed Senior-Løken syndrome, SLS). Linkage analyses, performed in 22 multiplex NPH families (18 without and 4 with ocular abnormalities), have localized the gene to a region between D2S48 and D2S51 on chromosome 2p. This was confirmed using adjacent microsatellite markers, one of which (AFM220ze3 at the D2S160 locus) gave a lod score of 4.78 at theta = 0.05 in the 18 families with isolated NPH, whereas the same marker excluded linkage with SLS. These results demonstrate linkage of the purely renal form of NPH to chromosome 2p, and suggest that there may be genetic heterogeneity between NPH and SLS.