Barttin is a Cl- channel beta-subunit crucial for renal Cl- reabsorption and inner ear K+ secretion

Renal salt loss in Bartter's syndrome is caused by impaired transepithelial transport in the loop of Henle. Sodium chloride is taken up apically by the combined activity of NKCC2 (Na+-K--2Cl- cotransporters) and ROMK potassium channels. Chloride ions exit from the cell through basolateral ClC-Kb chloride channels. Mutations in the three corresponding genes have been identified that correspond to Bartter's syndrome types 1-3. The gene encoding the integral membrane protein barttin is mutated in a form of Bartter's syndrome that is associated with congenital deafness and renal failure. Here we show that barttin acts as an essential beta-subunit for ClC-Ka and ClC-Kb chloride channels, with which it colocalizes in basolateral membranes of renal tubules and of potassium-secreting epithelia of the inner ear. Disease-causing mutations in either ClC-Kb or barttin compromise currents through heteromeric channels. Currents can be stimulated further by mutating a proline-tyrosine (PY) motif on barttin. This work describes the first known beta-subunit for CLC chloride channels and reveals that heteromers formed by ClC-K and barttin are crucial for renal salt reabsorption and potassium recycling in the inner ear.

Mutation of BSND causes Bartter syndrome with sensorineural deafness and kidney failure

Antenatal Bartter syndrome (aBS) comprises a heterogeneous group of autosomal recessive salt-losing nephropathies. Identification of three genes that code for renal transporters and channels as responsible for aBS has resulted in new insights into renal salt handling, diuretic action and blood-pressure regulation. A gene locus of a fourth variant of aBS called BSND, which in contrast to the other forms is associated with sensorineural deafness (SND) and renal failure, has been mapped to chromosome 1p. We report here the identification by positional cloning, in a region not covered by the human genome sequencing projects, of a new gene, BSND, as the cause of BSND. We examined ten families with BSND and detected seven different mutations in BSND that probably result in loss of function. In accordance with the phenotype, BSND is expressed in the thin limb and the thick ascending limb of the loop of Henle in the kidney and in the dark cells of the inner ear. The gene encodes a hitherto unknown protein with two putative transmembrane alpha-helices and thus might function as a regulator for ion-transport proteins involved in aBS, or else as a new transporter or channel itself.

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.

Recessive missense mutations in LAMB2 expand the clinical spectrum of LAMB2-associated disorders

Congenital nephrotic syndrome is clinically and genetically heterogeneous. The majority of cases can be attributed to mutations in the genes NPHS1, NPHS2, and WT1. By homozygosity mapping in a consanguineous family with isolated congenital nephrotic syndrome, we identified a potential candidate region on chromosome 3p. The LAMB2 gene, which was recently reported as mutated in Pierson syndrome (microcoria-congenital nephrosis syndrome; OMIM #609049), was located in the linkage interval. Sequencing of all coding exons of LAMB2 revealed a novel homozygous missense mutation (R246Q) in both affected children. A different mutation at this codon (R246W), which is highly conserved through evolution, has recently been reported as causing Pierson syndrome. Subsequent LAMB2 mutational screening in six additional families with congenital nephrotic syndrome revealed compound heterozygosity for two novel missense mutations in one family with additional nonspecific ocular anomalies. These findings demonstrate that the spectrum of LAMB2-associated disorders is broader than previously anticipated and includes congenital nephrotic syndrome without eye anomalies or with minor ocular changes different from those observed in Pierson syndrome. This phenotypic variability likely reflects specific genotypes. We conclude that mutational analysis in LAMB2 should be considered in congenital nephrotic syndrome, if no mutations are found in NPHS1, NPHS2, or WT1.

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.

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.

Homozygosity mapping of a gene locus for primary ciliary dyskinesia on chromosome 5p and identification of the heavy dynein chain DNAH5 as a candidate gene

Reduced mucociliary clearance in primary ciliary dyskinesia (PCD) causes recurrent infections of the upper and lower respiratory tract. The disease is usually inherited as an autosomal recessive trait. To identify a gene locus for PCD, we studied a large consanguineous family of Arabic origin. Direct examination of the respiratory cilia revealed ciliary akinesia. Electron microscopic examination of cilia showed absence of the outer dynein arms. Two of four affected individuals exhibited a situs inversus, typical for Kartagener syndrome, due to randomization of the left/right body axis. A total genome scan with 340 highly polymorphic microsatellites was performed. We localized a new gene locus for PCD to a region of homozygosity by descent on chromosome 5p15-p14 with a parametric multipoint logarithm of odds ratio (LOD) score of Zmax = 3.51 flanked by markers D5S2095 and D5S502 within an interval of 20 centimorgans sex-averaged genetic distance. Applying a polymerase chain reaction-based approach, we identified a 1.5-kb partial complementary DNA of DNAH5 encoding a Chlamydomonas-related axonemal heavy dynein chain within the critical disease interval of this new PCD locus. On the basis of the Chlamydomonas model for PCD, this gene represents an excellent candidate for PCD.

Hypomorphic mutations in meckelin (MKS3/TMEM67) cause nephronophthisis with liver fibrosis (NPHP11)

BACKGROUND

Nephronophthisis (NPHP), a rare recessive cystic kidney disease, is the most frequent genetic cause of chronic renal failure in children and young adults. Mutations in nine genes (NPHP1-9) have been identified. NPHP can be associated with retinal degeneration (Senior-Løken syndrome), brainstem and cerebellar anomalies (Joubert syndrome), or liver fibrosis.

METHODS

To identify a causative gene for the subset of patients with associated liver fibrosis, the authors performed a genome wide linkage search in a consanguineous family with three affected patients using 50K SNP microarrays and homozygosity mapping.

RESULTS

The authors obtained a significant maximum parametric LOD (logarithm of odds) score of Z(max) = 3.72 on chromosome 8q22 and identified a homozygous missense mutation in the gene MKS3/TMEM67. When examining a worldwide cohort of 62 independent patients with NPHP and associated liver fibrosis we identified altogether four novel mutations (p.W290L, p.C615R, p.G821S, and p.G821R) in five of them. Mutations of MKS3/TMEM67, found recently in Meckel-Gruber syndrome (MKS) type 3 and Joubert syndrome (JBTS) type 6, are predominantly truncating mutations. In contrast, the mutations detected here in patients with NPHP and associated liver fibrosis are exclusively missense mutations. This suggests that they may represent hypomorphic alleles, leading to a milder phenotype compared with the more severe MKS or JBTS phenotype. Additionally, mutation analysis for MKS3/TMEM67 in 120 patients with JBTS yielded seven different (four novel) mutations in five patients, four of whom also presented with congenital liver fibrosis.

CONCLUSIONS

Hypomorphic MKS3/TMEM67 mutations cause NPHP with liver fibrosis (NPHP11). This is the first report of MKS3 mutations in patients with no vermian agenesis and without neurological signs. Thus NPHP, JBTS, and MKS represent allelic disorders.

Nephrocystin interacts with Pyk2, p130(Cas), and tensin and triggers phosphorylation of Pyk2

Juvenile nephronophthisis type 1 is caused by mutations of NPHP1, the gene encoding for nephrocystin. The function of nephrocystin is presently unknown, but the presence of a Src homology 3 domain and its recently described interaction with p130(Cas) suggest that nephrocystin is part of the focal adhesion signaling complex. We generated a nephrocystin-specific antiserum and analyzed the interaction of native nephrocystin with endogenous proteins. Immunoprecipitation of nephrocystin revealed that nephrocystin forms protein complexes with p130(Cas), proline-rich tyrosine kinase 2 (Pyk2), and tensin, indicating that these proteins participate in a common signaling pathway. Expression of nephrocystin resulted in phosphorylation of Pyk2 on tyrosine 402 as well as activation of downstream mitogen-activated protein kinases, such as ERK1 and ERK2. Our findings suggest that nephrocystin helps to recruit Pyk2 to cell matrix adhesions, thereby initiating phosphorylation of Pyk2 and Pyk2-dependent signaling. A lack of functional nephrocystin may compromise Pyk2 signaling in a subset of renal epithelial cells.

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.

New insights: nephronophthisis-medullary cystic kidney disease

Nephronophthisis (NPH) and medullary cystic kidney disease (MCKD) constitute a group of renal cystic diseases, which share a common characteristic renal histologic triad of tubular basement membrane disintegration, tubular atrophy with cyst development, and interstitial cell infiltration with fibrosis. The different disease variants lead to chronic renal failure with onset at characteristic age ranges for recessive NPH and dominant MCKD. There is extensive gene locus heterogeneity with at least three different loci for nephronophthisis (NPHP1, NPHP2, and NPHP3) and two different loci for MCKD (MCKD1 and MCKD2). Juvenile nephronophthisis, in addition, can be associated with extrarenal organ involvement. We have identified by positional cloning the gene (NPHP1) for juvenile nephronophthisis (NPH1), as a first step towards understanding the pathogenesis of this disease group. Its gene product, nephrocystin, is a novel protein, which contains a src-homology 3 (SH3) domain. We put forward a hypothesis that the pathogenesis of NPH might be related to signaling processes at focal adhesions (the contact points between cells and extracellular matrix) and/or adherens junctions (the contact points between cells).

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.

Adenosine-triphosphate in trauma-related and elective hypothermia

BACKGROUND

In trauma patients, hypothermia is a frequent event. According to the literature, the majority of trauma patients are presenting a core temperature of less than 34 degrees C at admission. In contrast to the benefit of hypothermia in elective surgery, clinical experience with hypothermia in trauma patients has identified hypothermia to be one major cause of severe posttraumatic complications. It was hypothesized that this diverse effect of hypothermia is related to depletion of high-energy phosphates like adenosine triphosphate (ATP) in trauma patients. To verify this hypothesis, the relation of ATP plasma levels and hypothermia was examined in a clinical study.

METHODS

Three different groups of patients were under study. The first group (group A, normothermic control group) included patients (n = 15) undergoing elective surgery of the lower limb with a mean operation time of 113 minutes. The second study group (group B, hypothermic control) was composed of patients (n = 15) who were subjected to elective coronary artery bypass operation under hypothermia (31 degrees C for 48 minutes, mean total operation time being 205 minutes). The third study group (group C) included trauma patients (n = 23, mean Injury Severity Score [ISS] of 24.7). At the time of admission, 10 patients presented a core temperature more than or equal to 34 degrees C (group C1, mean ISS, 25.2; mean T(A), 34.5 degrees C), 13 patients presented a T(A) less than 34 degrees C (group C2, mean ISS, 26.0; mean T(A), 32.9 degrees C). In both groups of surgical patients, the ATP plasma level was measured preoperatively, at 2, 4, and 24 hours postoperatively. For trauma patients, this measurement was performed at admission and 24 hours later. Within the same schedule, body core temperature was recorded and the clinical course was documented as well.

RESULTS

Elective limb surgery in normothermic patients resulted only in a transient decrease in ATP plasma levels (preoperative, 87.8 micromol/dL; 4 hours postoperative, 52.0 micromol/dL). At 24 hours, the ATP plasma level (62.6 +/- 10.0 micromol/dL) has increased toward baseline level. Elective hypothermia in patients subjected to coronary bypass also resulted only in a transient decrease in ATP plasma levels. During the operation period, including hypothermia, the ATP plasma level was comparable (50.4 micromol/dL) to group A and also returned back toward normal values at 24 hours (58.2 micromol/dL). All trauma patients revealed a significant low ATP plasma level at admission compared with both control groups. Looking at subdivided groups the most significant drop in ATP plasma level (28.5 micromol/dL) was noted in patients presenting an initial core temperature less than 34 degrees C and ISS more than 30. Even 24 hours later, the ATP level of this subgroup was significantly diminished, despite a rise up to 44.4 micromol/dL. In contrast, only a moderate drop in ATP plasma concentration (59.2 micromol/dL) was noted in the group of T(A) more than or equal to 34 degrees C and ISS less than 20. This group revealed almost normal values (68.3 micromol/dL) 24 hours after trauma. In addition to hypothermia, the metabolic state, reflected by the plasma lactate levels, significantly influenced the ATP plasma levels, as high lactate levels were paralleled by low ATP levels. Also, the overall outcome was related to injury severity and hypothermia.

CONCLUSION

Hypothermia in elective surgery, established by active cooling, preserves the ATP storage and maintains an aerobic metabolism, which both contribute to the beneficial effect of hypothermia in ischemia/reperfusion in cardiovascular surgery. However, in trauma patients hypothermia is caused by insufficient heat production due to utilization of ATP under anaerobic metabolic conditions. Low ATP plasma levels combined with hypothermia seem to be a predisposition for post-traumatic complications like organ failure.

Secondary nephrogenic diabetes insipidus as a complication of inherited renal diseases

BACKGROUND/AIMS

Nephrogenic diabetes insipidus (NDI) is a serious condition with large water losses in the urine and the risk of hypernatremic dehydration. Unrecognized, repeated episodes of hypernatremic dehydration can lead to permanent brain damage. Primary NDI is due to mutations in either AVPR2 or AQP2. NDI can also occur as a secondary complication, most commonly from obstructive uropathy or chronic lithium therapy. We observed NDI in patients with inherited tubulopathies and aimed to define the clinical and molecular phenotype.

METHODS

We reviewed the medical notes of 4 patients with clinical NDI and an underlying molecularly confirmed diagnosis of nephropathic cystinosis, Bartter syndrome, nephronophthisis and apparent mineralocorticoid excess, respectively.

RESULTS

The patients all failed to concentrate their urine after administration of 1-desamino[8-D-arginine] vasopressin. None had an identifiable mutation in AVPR2 or AQP2, consistent with secondary NDI. Patients experienced repeated episodes of hypernatremic dehydration, and in 2 cases, NDI was initially thought to be the primary diagnosis, delaying recognition of the underlying problem.

CONCLUSION

The recognition of this potential complication is important as it has direct implications for clinical management. The occurrence of NDI in association with these conditions provides clues for the etiology of aquaporin deficiency.

WDR19: an ancient, retrograde, intraflagellar ciliary protein is mutated in autosomal recessive retinitis pigmentosa and in Senior-Loken syndrome

Autosomal recessive retinitis pigmentosa (arRP) is a clinically and genetically heterogeneous retinal disease that causes blindness. Our purpose was to identify the causal gene, describe the phenotype and delineate the mutation spectrum in a consanguineous Quebec arRP family. We performed Arrayed Primer Extension (APEX) technology to exclude ∼500 arRP mutations in ∼20 genes. Homozygosity mapping [single nucleotide polymorphism (SNP) genotyping] identified 10 novel significant homozygous regions. We performed next generation sequencing and whole exome capture. Sanger sequencing provided cosegregation. We screened another 150 retinitis pigmentosa (RP) and 200 patients with Senior-Løken Syndrome (SLS). We identified a novel missense mutation in WDR19, c.2129T>C which lead to a p.Leu710Ser. We found the same mutation in a second Quebec arRP family. Interestingly, two of seven affected members of the original family developed 'sub-clinical' renal cysts. We hypothesized that more severe WDR19 mutations may lead to severe ciliopathies and found seven WDR19 mutations in five SLS families. We identified a new gene for both arRP and SLS. WDR19 is a ciliary protein associated with the intraflagellar transport machinery. We are currently investigating the full extent of the mutation spectrum. Our findings are crucial in expanding the understanding of childhood blindness and identifying new genes.

Establishing an algorithm for molecular genetic diagnostics in 127 families with juvenile nephronophthisis

BACKGROUND

Juvenile nephronophthisis (NPH1), an autosomal recessive cystic disease of the kidney, represents the most common genetic cause of end-stage renal disease in the first two decades of life. On the basis of identification of the gene (NPHP1) defective in NPH1 and the presence of homozygous deletions of NPHP1 in the majority of NPH1 patients, molecular genetic diagnosis for NPH1 is now possible. Molecular genetic testing offers the only method for definite diagnosis of NPH1 and avoids invasive diagnostic measures like renal biopsy.

METHODS

We examined 127 families (204 patients) with the presumed diagnosis of NPH using molecular genetic diagnostic techniques. In 68 families, renal biopsy was performed and was consistent with NPH, and in 61 families, there was more than one affected child ("multiplex families").

RESULTS

In 74 families (115 patients), there was proof of the diagnosis of NPH1 by detection of a homozygous deletion of the NPHP1 gene, and in 5 families a heterozygous deletion in combination with a point mutation in NPHP1 was demonstrated. Furthermore, for 16 families, NPH1 was excluded with high likelihood by linkage analysis, and for 20 families by detection of heterozygosity for two newly identified polymorphic markers within the deletion region. In 5 of the remaining 12 families, which were noninformative for these markers, fluorescence in situ hybridization did not detect any further heterozygous deletions.

CONCLUSIONS

The diagnosis of NPH1 was proven by molecular genetic techniques in 62% of families with one or more children with the presumed diagnosis of NPH. We present evidence that there is a fourth locus for NPH, since only 6 of the 26 multiplex families in whom the diagnosis of NPH1 was excluded were compatible with linkage to other loci for NPH. On the basis of the presented data, we propose an algorithm for molecular genetic diagnostics in NPH.

The nephronophthisis complex: clinical and genetic aspects

Familial juvenile nephronophthisis (NPH) and medullary cystic disease (MCD) are hereditary forms of early-onset chronic renal failure caused by the bilateral formation of cysts at the corticomedullary junction of the kidney. Polyuria, polydipsia, anemia, and growth retardation precede end-stage renal failure. The absence of edema and hypertension frequently leads to a delay in the diagnosis and commencement of therapy. The condition is a major cause of end-stage renal disease (ESRD) in children, accounting for 10%-25% of these patients. About 300 cases of NPH or MCD have been described. Although they are almost indistinguishable clinically and pathologically, the two conditions are separated by a characteristic age of onset (11.5 years in NPH vs. 28.5 years in MCD) and by the mode of inheritance (autosomal recessive in NPH vs. autosomal dominant in MCD). An association of NPH with retinitis pigmentosa is known as the Senior-Løken syndrome (SLS). Hepatic fibrosis, skeletal defects, and central nervous system abnormalities have been described in association with NPH but are typically absent in MCD. Since the pathology of NPH and MCD is similar, the term "nephronophthisis complex" has been introduced to summarize the related diseases. At present, there are no means of identifying heterozygotes, conducting prenatal diagnosis, or screening children in affected families. The histologic changes of NPH are characteristic but not specific for the disease. Cysts of 1-15 mm in diameter, located primarily at the corticomedullary junction, are seen in 70% of the patients. Light microscopy reveals a chronic sclerosing tubulo-interstitial nephropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

The Uromodulin C744G mutation causes MCKD2 and FJHN in children and adults and may be due to a possible founder effect

Autosomal dominant medullary cystic kidney disease type 2 (MCKD2) is a tubulo-in terstitial nephropathy that causes renal salt wasting, hyperuricemia, gout, and end-stage renal failure in the fifth decade of life. This disorder was described to have an age of onset between the age of 20-30 years or even later. Mutations in the Uromodulin (UMOD) gene were published in patients with familial juvenile hyperuricemic nephropathy (FJHN) and MCKD2. Clinical data and blood samples of 16 affected individuals from 11 different kindreds were collected. Mutational analysis of the UMOD gene was performed by exon polymerase chain reaction (PCR) and direct sequencing. We found the heterozygous C744G (Cys248Trp) mutation, which was originally published by our group, in an additional four kindreds from Europe and Turkey. Age of onset ranged from 3 years to 39 years. The phenotype showed a variety of symptoms such as urinary concentration defect, vesicoureteral reflux, urinary tract infections, hyperuricemia, hypertension, proteinuria, and renal hypoplasia. Haplotype analysis showed cosegragation with the phenotype in all eight affected individuals indicating that the C744G mutation may be due to a founder effect. Moreover, we describe a novel T229G (Cys77Gly) mutation in two affecteds of one kindred. Three of the affected individuals were younger than 10 years at the onset of MCKD2/FJHN. Symptoms include recurrent urinary tract infections compatible with the published phenotype of the Umod knockout mouse model. This emphasizes that MCKD2 is not just a disease of the young adult but is also relevant for children.

Hereditary isolated renal magnesium loss maps to chromosome 11q23

Hypomagnesemia due to isolated renal magnesium loss has previously been demonstrated in two presumably unrelated Dutch families with autosomal dominant mode of inheritance. Patients with magnesium deficiency may suffer from tetany and convulsions, but the patients with hereditary renal magnesium wasting can also be clinically nonsymptomatic. In a genomewide linkage study, we first excluded a possible candidate region, on chromosome 9q, that encompasses the gene for intestinal hypomagnesemia with secondary hypocalcemia and, subsequently, found linkage to markers on chromosome 11q23. Detailed haplotype analyses identified a common haplotype segregating in both families, suggesting both their relationship through a common ancestor and the existence of a single, hypomagnesemia-causing mutation within them. The maximum two-point LOD score (Zmax) was found for marker D11S4127 (Zmax=6.41 at a recombination fraction of. 00), whereas a multipoint analysis gave a Zmax of 8.24 between markers D11S4142 and D11S4171. Key recombination events define a 5. 6-cM region between these two markers on chromosome 11q23. We conclude that this region encompasses a gene, involved in renal magnesium handling, that is mutated in our patients and is different from the gene involved in intestinal magnesium handling.

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.

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.

Multiple trauma induces serum production of host defence peptides

Today multiple trauma still is associated with a high mortality. Although severe open fractures and wounds can give rise to local infections and sepsis, the overall infection rate of multiply injured patients is surprisingly low. We have investigated serum of multiply injured patients with respect to antibacterial properties and screened for host defence peptides (HDP) that constitute a class of fast acting and rapidly available molecules preventing bacterial infection. Serum specimens were obtained from multiply injured patients. Radial diffusion assays were performed to investigate antimicrobial properties. Ultrafiltration and heat-inactivation were used to rule out antimicrobial activity of large proteins i.e. complement factors. ELISA was performed to analyse serum concentrations of the human beta-defensins 2 and 3 (hBD-2 and hBD-3), LL-37 and the proinflammatory cytokines interferon-gamma (IFN-γ) and interleukin-6 (IL-6). Serum of multiply injured patients showed greater zones of inhibition in antimicrobial testing against Gram negative und positive bacteria. This effect was mediated by proteins smaller than 10 kDa, inactivation of the complement system does not significantly reduce antibacterial action. hBD-2, hBD-3 and LL-37 concentrations were significantly elevated after trauma and followed different characteristic concentration curves. Similar patterns of concentration profiles were recorded for hBD-2/IL-6 and hBD-3/IFN-γ suggesting a stimulatory influence within their induction process. With this study we provide evidence, that serum of multiply injured patients has by far higher antibacterial capacity than that of healthy donors. As possible mediators we have detected the HDP hBD-2, hBD-3 and LL-37 and their inducers in serum of multiply injured patients.

Appearance of autosomal recessive polycystic kidney disease in magnetic resonance imaging and RARE-MR-urography

PURPOSE

To describe the appearance of autosomal recessive polycystic kidney disease (ARPKD) on MRI and RARE-MR urography.

MATERIALS AND METHODS

Seven boys and one girl (aged 3 months to 14 years, median 2.5 years) were evaluated. Images were obtained with 0.23-T and 1.5-T MR systems using T1-weighted (T1-W) spin-echo, T2-weighted (T2-W) turbo-spin-echo and RARE-MR-urography sequences. Signal intensities, morphological appearance of the affected kidneys and, specifically, the picture of the urinary tract on RARE-MR-urography were evaluated.

RESULTS

All children showed kidney enlargement, reniform but humpy kidney shape, homogeneously grainy renal parenchyma, normal renal pelvis and normal calyces. Signal intensity was hyperintense in T2-W images in all cases. In six cases (n = 7), T1-W images were hypointense. On RARE-MR urography a hyperintense, linear radial pattern was seen in the cortex and medulla which represents the characteristic microcystic dilatation of collecting ducts in ARPKD. Three boys and the girl presented with a few circumscribed small subcapsular cysts.

CONCLUSIONS

In order to confirm the diagnosis of ARPKD, RARE-MR urography seems to be a non-invasive imaging tool that shows directly the microcystic dilated water-filled collecting ducts.