BSND Research Articles

Clinical Features and Unusual Heterozygous Mutations in Patients with Renal Hypokalemia.

Renal hypokalemia is associated with mutation. This study aimed to investigate the clinical features and pathogenic mutations in patients with renal hypokalemia. The patients with hypokalemia were enrolled, and the renal function, thyroid function, renin-aldosterone system, urinary potassium excretion, and exome sequencing were performed. The correlation between the clinical phenotypes and causative genes was assessed. Five patients with hypokalemia were enrolled and diagnosed as tubular hypokalemia. The patients with common clinical manifestations were difficult to differentiate based on atypical laboratory findings. The results of the genetic analysis were as follows: both patient 1 and patient 2 were heterozygous for the c.C625T mutation of the KCNJ1 gene, which is responsible for Bartter syndrome. Patient 3 was heterozygous for the c.G298A mutation of the ATP6V1B1 gene, which is responsible for renal tubular acidosis. Patient 4 had a compound heterozygous mutation of c.G893A of the BSND gene, responsible for Bartter syndrome, and c.1029+5G>A, the ATP6V0A4 gene responsible for distal renal tubular acidosis. Patient 5 had Gitelman syndrome and carried the compound heterozygous mutations c.C1963T and c.G2029A of the SLC12A3 gene. All the above loci were known heterozygous mutations. The unusual heterozygous mutations were identified in five renal hypokalemia patients. Molecular diagnosis of tubular hypokalemia was conducive to accurate diagnosis and treatment.

Clinical Findings and Genetic Analysis of Nine Mexican Families with Bartter Syndrome

Bartter's syndrome (BS) is a group of salt-wasting tubulopathies characterized by hypokalemia, metabolic alkalosis, hypercalciuria, secondary hyperaldosteronism, and low or normal blood pressure. Loss-of-function variants in genes encoding for five proteins expressed in the thick ascending limb of Henle in the nephron, produced different genetic types of BS. Clinical and genetic analysis of families with Antenatal Bartter syndrome (ABS) and with Classic Bartter syndrome (CBS). Nine patients from unrelated non-consanguineous Mexican families were studied. Massive parallel sequencing of a gene panel or whole-exome sequencing was used to identify the causative gene. Proband 1 was homozygous for the pathogenic variant p.Arg302Gln in the SLC12A1 gene encoding for the sodium-potassium-chloride NKCC2 cotransporter. Proband 3 was homozygous for the nonsense variant p.Cys308* in the KCNJ1 gene encoding for the ROMK potassium channel. Probands 7, 8, and 9 showed variants in the CLCKNB gene encoding the chloride channel ClC-Kb: proband 7 was compound heterozygous for the deletion of the entire gene and the missense change p.Arg438Cys; proband 8 presented a homozygous deletion of the whole gene and proband 9 was homozygous for the nonsense mutation p.Arg595*. A heterozygous variant of unknown significance was detected in the SLC12A1 gene in proband 2, and no variants were found in SLC12A1, KCNJ1, BSND, CLCNKA, CLCNKB, and MAGED2 genes in probands 4, 5, and 6. Genetic analysis identified loss-of-function variants in the SLC12A1, KCNJ1, and CLCNKB genes in four patients with ABS and in the CLCNKB gene in two patients with CBS.

An Unusual Case of BSND Gene–Related (Type IV) Bartter Syndrome Presenting as Antenatal Bartter Syndrome: A Case Report and Review of Literature

Abstract Bartter syndrome is a group of autosomal recessive renal tubular disorders; it has two types of presentation: antenatal and classic. The antenatal type presents as severe unexplained polyhydramnios in the second trimester. This is due to fetal urinary losses of sodium, chloride, and potassium, leading to fetal polyuria. The classic type presents in the late neonatal or infancy stage, with dehydration, dyselectrolytemia, failure to thrive, and nephrocalcinosis. Antenatal scans are normal in such cases. Type I and II Bartter syndrome presents in the antenatal period, whereas type IV has a classic presentation. We describe an unusual case of type IVa Bartter syndrome presenting in the antenatal period, with severe polyhydramnios. The initial diagnosis was made based on amniotic fluid chloride levels and later confirmed by performing a genetic test. Genetic testing is important for confirming diagnosis and prognostication regarding the condition.

ClC-K Kidney Chloride Channels: From Structure to Pathology.

The molecular basis of chloride transport varies all along the nephron depending on the tubular segments especially in the apical entry of the cell. The major chloride exit pathway during reabsorption is provided by two kidney-specific ClC chloride channels ClC-Ka and ClC-Kb (encoded by CLCNKA and CLCNKB gene, respectively) corresponding to rodent ClC-K1 and ClC-K2 (encoded by Clcnk1 and Clcnk2). These channels function as dimers and their trafficking to the plasma membrane requires the ancillary protein Barttin (encoded by BSND gene). Genetic inactivating variants of the aforementioned genes lead to renal salt-losing nephropathies with or without deafness highlighting the crucial role of ClC-Ka, ClC-Kb, and Barttin in the renal and inner ear chloride handling. The purpose of this chapter is to summarize the latest knowledge on renal chloride structure peculiarity and to provide some insight on the functional expression on the segments of the nephrons and on the related pathological effects.

Twelve exonic variants in the SLC12A1 and CLCNKB genes alter RNA splicing in a minigene assay.

Background: Bartter syndrome (BS) is a rare renal tubular disease caused by gene variants in SLC12A1, KCNJ1, CLCNKA, CLCNKB, BSND or MAGED2 genes. There is growing evidence that many exonic mutations can affect the pre-mRNA normal splicing and induce exon skipping by altering various splicing regulatory signals. Therefore, the aim of this study was to gain new insights into the consequences of exonic mutations associated with BS on pre-mRNA splicing. Methods: We analyzed all the missense, nonsense and synonymous variants described in six pathogenic genes by bioinformatics programs and identified candidate mutations that may promote exon skipping through a minigene system. Results: Results of the study showed that 12 of 14 candidate variants distributed in SLC12A1 (c.728G>A, C.735C>G, c.904C>T, c.905G>A, c.1304C>T, c.1493C>T, c.2221A>T) and CLCNKB (c.226C>T, c.228A>C, c.229G>A, c.229G>C, c.1979C>A) were identified to induce splicing alterations. These variants may not only disrupt exonic splicing enhancers (ESEs) but also generate new exonic splicing silencers (ESSs), or disturb the classic splicing sites. Conclusion: To our knowledge, this is a comprehensive study regarding alterations in pre-mRNA of exonic variants in BS pathogenic genes. Our results reinforce the necessity of assessing the consequences of exonic variants at the mRNA level.

Phenotypic and genotypic characteristics of children with Bartter syndrome.

Bartter syndrome (BS) is a group of autosomal-recessive tubular disorders and it is classified into five genetic subtypes. BS can also be classified by phenotype (antenatal, classic). Patients with mutations in the same gene can present different phenotypes. In the present study, target gene sequencing was performed to evaluate the genotype-phenotype relationship. Biochemical, clinical and renal ultrasonography results were collected at presentation and the last clinic visit. Genetic analyses were performed. The findings of patients with classical BS (cBS) and antenatal BS (aBS) at presentation and the last visit were compared. Our study included 21 patients (12 female, 57.1%) from 20 families with BS. The median age at diagnosis was 8 months and the median follow-up period was 39 months. The most frequent complaint was growth failure. We have found 18 different types of mutations in four genes, including nine in the CLCNKB gene, seven in the SLCA12A1 gene, one in the KCNJ1 gene and one in the BSND gene. In ten patients, nine different types of CLCNKB gene mutations were detected, five of them were novel. Seven different mutations in the SLC12A1 gene were detected in eight patients, five of them were novel. Compared to patients with aBS and cBS, prematurity was significantly higher in the group with aBS. Nephrocalcinosis was present in only one patient with cBS, all the ten hypercalciuric patients with aBS had nephrocalcinosis at the time of diagnosis and the last visit. The mean height standard deviation score (SDS) of patients with aBS were significantly lower than the cBS group at the time of presentation. The mean weight SDS at the time of presentation was worse in patients with aBS than in patients with cBS. The mean plasma potassium and chloride concentrations were significantly lower in the patients with cBS at the time of diagnosis. This investigation revealed the mutation characteristics and phenotype-genotype relationship of our patients and provided valuable data for genetic counseling.

Severe polyhydramnios as neonatal presentation of Bartter’s syndrome type IV

Abstract Introduction: Bartter’s syndrome comprises a heterogeneous group of inherited salt-losing tubulopathies. There are two forms of clinical presentation: classical and neonatal, the most severe type. Types I and II account for most of the neonatal cases. Types III and V are usually less severe. Characteristically Bartter’s syndrome type IV is a saltlosing nephropathy with mild to severe neonatal symptoms, with a specific feature - sensorineural deafness. Bartter’s syndrome type IV is the least common of all recessive types of the disease. Description: the first reported case of a Portuguese child with neurosensorial deafness, polyuria, polydipsia and failure to thrive, born prematurely due to severe polyhydramnios, with the G47R mutation in the BSND gene that causes Bartter’s syndrome type IV. Discussion: there are few published cases of BS type IV due to this mutation and those reported mostly have moderate clinical manifestations which begin later in life. The poor phenotype-genotype relationship combined with the rarity of this syndrome usually precludes an antenatal diagnosis. In the presence of a severe polyhydramnios case, with no fetal malformation detected, normal karyotype and after maternal disease exclusion, autosomal recessive diseases, including tubulopathies, should always be suspected.

POS-097 BARTTER'S SYNDROM AND DEAFNESS: A CASE REPORT

Bartter's syndrome exhibits genetic heterogeneity. The neonatal form with deafness is due to mutations in the BSND gene encoding a subunit of the chlorine channels ClC-Ka and ClC-Kb (Bartter type IV). We report the case of a patient with Bartter syndrome associated with bilateral deafness 18-year-old patient with a family history of a niece with bartter syndrome, 2 sisters who died in the neonatal period and 4 late abortions in the mother’s medical history. Personal history of inbreeding. Resulting from a complicated hydramnios pregnancy with low birth weight. Followed since the age of 10 months for failure to thrive and facial dysmorphism with an episode of meningoencephalitis at the age of 1 year. The diagnosis of bartter syndrome was made at the age of 3 years due to hypokalaemia with high kaliuresis, metabolic alkalosis with polyuropolydipsia treated with potassium supplementation and NSAIDs. In view of hydramnios, dysmorphia and deafness, type IV bartter was suspected, confirmed by a genetic study showing the mutation of the BSND gene. After 15 years of follow-up after the positive diagnosis, polyuria was moderate at 3l / d with hypokalaemia at 2.2 mmol / l and moderate renal failure. This observation is distinguished by the association of bartter syndrome with deafness and a facial dysmorphism, as well as a progressive evolution despite the severity of the initial presentation. Bartter's syndrome is a rare condition whose prognosis is dominated by the severity of the hydroelectrolyte disturbances and the risk of chronic kidney disease. Type IV is a rare neonatal form associated with neurogenic deafness that progresses early to chronic renal failure. The immediate severity of this disease requires careful monitoring of pregnancy and birth

Functional Study of Novel Bartter's Syndrome Mutations in ClC-Kb and Rescue by the Accessory Subunit Barttin Toward Personalized Medicine.

Type III and IV Bartter syndromes (BS) are rare kidney tubulopathies caused by loss-of-function mutations in the CLCNKB and BSND genes coding respectively for the ClC-Kb chloride channels and accessory subunit barttin. ClC-K channels are expressed in the Henle’s loop, distal convoluted tubule, and cortical collecting ducts of the kidney and contribute to chloride absorption and urine concentration. In our Italian cohort, we identified two new mutations in CLCNKB, G167V and G289R, in children affected by BS and previously reported genetic variants, A242E, a chimeric gene and the deletion of the whole CLCNKB. All the patients had hypokalemia and metabolic alkalosis, increased serum renin and aldosterone levels and were treated with a symptomatic therapy. In order to define the molecular mechanisms responsible for BS, we co-expressed ClC-Kb wild type and channels with point mutations with barttin in HEK 293 cells and characterized chloride currents through the patch-clamp technique. In addition, we attempted to revert the functional defect caused by BS mutations through barttin overexpression. G167V and A242E channels showed a drastic current reduction compared to wild type, likely suggesting compromised expression of mutant channels at the plasma membrane. Conversely, G289R channel was similar to wild type raising the doubt that an additional mutation in another gene or other mechanisms could account for the clinical phenotype. Interestingly, increasing ClC-K/barttin ratio augmented G167V and A242E mutants’ chloride current amplitudes towards wild type levels. These results confirm a genotype-phenotype correlation in BS and represent a preliminary proof of concept that molecules functioning as molecular chaperones can restore channel function in expression-defective ClC-Kb mutants.

Hypokalemia and hearing loss in a 3-year-old boy: Questions.

Bartter syndrome with sensorineural deafness (Bartter syndrome type 4) is an autosomal recessive disorder characterized with polyhydramniosis, premature birth, massive polyuria, renal salt-wasting, hypokalemic metabolic alkalosis, normotensive hyperreninemic hyperaldosteronism, and hearing loss. Homozygous mutations in BSND, CLCNKA, and CLCNKB mutations cause the disorder. Here we report a 3-year-old boy who had not been evaluated and investigated before cochlear implantation. Hypokalemia was detected during the routine laboratory workup before surgery. Further analyses revealed metabolic alkalosis with high renin and aldosterone levels. Hypokalemia improved with oral potassium chloride supplementation. Genetic tests revealed a homozygous c.139G>A (pG47R) mutation in BSND gene, and both parents were heterozygous for the same mutation. We want to emphasize the importance of evaluating hearing loss in children, since some of the genetic syndromes may cause life threatening abnormalities.

Two novel homozygous missense mutations identified in the BSND gene in Moroccan patients with Bartter's syndrome

ObjectivesHearing loss (HL) is one of the most common sensorineural disorders. In the present study, we identified two novel missense mutations in BSND gene causing Bartter syndrome type IV which is a genetic disease with an autosomal recessive transmission, characterized by hypokalaemia, metabolic alkalosis, an elevation in plasma renin activity and hyperaldosteronism as well as sensorineural deafness. MethodsWhole-exome sequencing was performed to study the genetic causes of Hearing loss in two unrelated patients from two Moroccan families. ResultsThe two novel homozygous mutations p.Arg8Gly (c.22C > G), p.Thr36Asn (c.107C > A) in exon 1 of BSND gene which encodes barttin were identified in 7 patients belonging to two unrelated families originated from central region of Morocco. ConclusionWe identified two novel missense mutations p.Arg8Gly and p.Thr36Asn in exon 1 of BSND gene; both mutations were described for the first time in Moroccan patients with Bartter syndrome type IV.

Ultrasound findings provide clues to investigate founder mutations expressed as runs of homozygosity in chromosomal microarray studies.

Chromosomal microarray analysis is effectively applied prenatally to detect copy number changes. Single nucleotide polymorphism (SNP) probes included in the microarray platform can detect regions of excessive homozygosity and identical-by-descent genomic stretches. The utility of the latter as part of prenatal diagnosis is not well established. Recessive founder mutations are well recognized within distinct ethnic groups. Combining these data with prenatal sonography provides accurate focused molecular diagnoses quickly. We aimed to evaluate the application of this approach in expectant families presenting to our unit. Three unrelated gravidae presenting with specific fetal sonographic findings: (1) ventriculomegaly with encephalocele; (2) severe polyhydramnion; and (3) enlarged echogenic kidneys, underwent amniocentesis for chromosomal microarray analysis, and genome-wide human SNP array was used to analyze DNA from amniocytes. The Genomic Oligoarray and SNP array evaluation tool v3.0© was used to detect recessive loci associated with the reported clinical findings. Candidate genes were further interrogated using the Israeli National Genetic Database (INGD) and specifically searching and identifying a corresponding founder mutation within the defined ethnic group. Three fetuses from 3 distinct nuclear families in which the parents shared a similar ethnicity (either Ashkenazi or Bukharan Jews) albeit no reported consanguinity were assessed. We found no copy number changes; however, by evaluating regions of homozygosity, we were able to reveal relevant candidate gene for the specific phenotype for each fetus. Using the INGD led to targeted testing of a specific homozygous fetal mutation for which parents were found to be carriers. In the fetus with ventriculomegaly with encephalocele c.1167dupA mutation in the FKTN gene, in the fetus with severe polyhydramnion c.167ins6[TTTCCC] mutation in the BSND gene, and in the fetus with enlarged echogenic kidneys, c.3761_3762delCCinsG in the PKHD1 gene were identified. A tripartite approach integrating sonographic pathology with regions of excessive homozygosity data and INGD-based founder mutation repository yields a comprehensive streamlined approach to provide accurate genetic diagnosis and counselling within the time constraints of an ongoing pregnancy.

French cohort of transient antenatal Bartter syndrome with MAGED2 mutations

Background MAGED2 was recently identified in an X-linked severe and transient form of antenatal Bartter's syndrome associated with polyhydramnios and prematurity but also in idiopathic polyhydramnios in the male offspring. An inappropriate expression of the sodium-chloride transporters NKCC2 and NCC is disclosed. Methods MAGED2 was screened by Sanger Sequencing in a series of 35 cases with transient or antenatal Bartter's syndrome and no pathogenic variant in SLC12A1, KCNJ1, CLCNKB and BSND genes. Results We found 15 cases from 14 families harboring MAGED2 variants including four nonsense, three miss sense, two frame shift and two splice-site variants; two small in frame deletions and one complete deletion of MAGED2 gene. Only one variant was previously reported, p.Arg446Cys. Severe polyhydramnios occurred in all pregnancies, at 18 to 25 weeks of gestation requiring serial amniocentesis (one to ten, when data available). In four cases, polyhydramnios was present in previous or later pregnancies. One pregnancy resulted in medical termination of pregnancy. All the infants (14) were born pre-term with gestational age at delivery between 26 and 36 weeks. All presented a Bartter's syndrome with severe polyuria (median diuresis was 13 mL/kg/h). Surprisingly, two cases were females. The severity of their phenotype and the course of the disease were comparable to those for male. The medical follow-up of 12 patients revealed that the salt and water losses resolved between 2 and 18 months with the end of indomethacin treatment or water and salts supplements. Two cases, with associated neurological disorders died at 1 and 12 months. Conclusion We confirmed with our French series of 15 MAGED2 cases the phenotypic presentation of this transient antenatal Bartter's syndrome. This new syndrome has to be considered in the differential diagnosis of Bartter's syndrome with the screening of MAGED2 as part of the molecular diagnosis.

Mutation spectrum of Chinese patients with Bartter syndrome.

ObjectiveBartter syndrome (BS) has been rarely reported in Chinese population except for a few case reports. This investigation was aimed to analyze the mutations of the causal genes in sixteen Chinese patients with BS, and review their followup and treatment.MethodsIdentify mutations by the next generation sequencing and the multiplex ligation-dependent probe amplification (MLPA). Clinical characteristics and biochemical findings at the first presentation as well as follow-up were reviewed.Results15 different CLCNKB gene mutations were identified in fourteen patients with BS, including 11 novel ones. A novel missense mutation and a novel small deletion were found from SLC12A1 gene. A novel gross deletion was found in CLCNKA gene. A recurrent missense mutation was identified from BSND gene. We found that the whole gene deletion mutation of CLCNKB gene was the most frequent mutation (32%), and the rate of gross deletion was up to 50 percent in this group of Chinese patients.ConclusionThe present study has found 19 mutations, including 14 novel ones, which would enrich the human gene mutation database (HGMD) and provide valuable references to the genetic counseling and diagnosis of the Chinese population.

OP22.08: Integrating ultrasound findings with chromosomal microarray stretches of homozygosity and principles in founder populations

Chromosomal microarray (CMA) analysis is effectively applied prenatally to detect copy number changes. SNP probes included on the microarray platform can detect regions of excessive homozygosity (ROH) and identical-by-descent genomic stretches. The utility of the latter in prenatal diagnosis is not well established. Recessive founder mutations have been identified within distinct ethnic groups. Combining these data with prenatal sonography provides accurate molecular diagnoses quickly. Three gravidae presenting with specific fetal sonographic findings: 1) ventriculomegaly with encephalocele; 2) severe polyhydramnion, and 3) enlarged echogenic kidneys, underwent amniocentesis for CMA, and Genome-Wide Human SNP array was used to analyse DNA from amniocytes. The Genomic Oligoarray and SNP array evaluation tool v3.0 was used to detect recessive loci associated with the reported clinical findings. Candidate regions were further interrogated using the National Genetic Database. Three fetuses from three distinct nuclear families in which the parents shared a similar ethnicity (either Ashkenazi or Bukharan Jews) but no reported consanguinity, were assessed. No copy number changes were observed, however evaluation of regions of homozygosity revealed a relevant candidate gene for the specific phenotype for each fetus. Using the National Genetic Database a specific mutation was examined in both parents (c.1167dupA mutation in the FKTN gene, c.167ins6[TTTCCC] mutation in the BSND gene and c.3761_3762delCCinsG in the PKHD1 gene, respectively). Both parents were found to be carriers and the fetuses homozygotes to the mutation. For the first time, specific sonographic pathology, data from ROH extracted from CMA results, and information regarding common founder mutations in distinct ethnic subgroups were combined to create a comprehensive streamlined approach to provide effective genetic diagnosis and counselling within the time constraints of ongoing pregnancy.

A unique finding of normal aldosterone level in Bartter’s syndrome

Background: Bartter’s syndrome is a rare autosomal recessive renal tubular disorder characterized by hypokalemia, hypochloremia, metabolic alkalosis, hyperreninemia and hyperaldosteronemia with normotension. Bartter syndrome has five types; type 1 (mutation in sodium/potassium chloride transporter), type 2 (mutation in voltage gated potassium channel), type 3 (mutation on chromosome 1 that encodes Barttin and makes only kidney-specific chloride channel B non-functional), type 4 ( mutation in BSND gene encoding Barttin and makes both kidney-specific chloride channels A & B non-functional) and type 5 (L125P gain in function mutation in calcium-sensing receptor). Case Presentation: A 28-year-old male was hospitalized for evaluation of nausea, vomiting, generalized weakness and persistent chronic hypokalemia. Bartter’s syndrome was suspected based on clinical and laboratory evidence, however serum aldosterone level was normal. Further genetic testing confirmed the diagnosis of Bartter’s syndrome type 3. Conclusions: We report a case of Bartter’s syndrome type 3 with a unique finding of normal aldosterone level.

Pharmacovigilance database search discloses ClC-K channels as a novel target of the AT1 receptor blockers valsartan and olmesartan.

Human ClC-K chloride channels are highly attractive targets for drug discovery as they have a variety of important physiological functions and are associated with genetic disorders. These channels are crucial in the kidney as they control chloride reabsorption and water diuresis. In addition, loss-of-function mutations of CLCNKB and BSND genes cause Bartter's syndrome (BS), whereas CLCNKA and CLCNKB gain-of-function polymorphisms predispose to a rare form of salt sensitive hypertension. Both disorders lack a personalized therapy that is in most cases only symptomatic. The aim of this study was to identify novel ClC-K ligands from drugs already on the market, by exploiting the pharmacological side activity of drug molecules available from the FDA Adverse Effects Reporting System database. We searched for drugs having a Bartter-like syndrome as a reported side effect, with the assumption that BS could be causatively related to the block of ClC-K channels. The ability of the selected BS-causing drugs to bind and block ClC-K channels was then validated through an integrated experimental and computational approach based on patch clamp electrophysiology in HEK293 cells and molecular docking simulations. Valsartan and olmesartan were able to block ClC-Ka channels and the molecular requirements for effective inhibition of these channels have been identified. These results suggest additional mechanisms of action for these sartans further to their primary AT1 receptor antagonism and propose these compounds as leads for designing new potent ClC-K ligands.

Severe manifestation of Bartter syndrome Type IV caused by a novel insertion mutation in the BSND gene

Bartter syndrome Type IV is a rare subtype of the Bartter syndromes that leads to both severe renal salt wasting and sensorineural deafness. This autosomal recessive disease is caused by mutations in the gene encoding barttin, BSND, an essential subunit of the ClC-K chloride channels expressed in renal and inner ear epithelia. Patients differ in the severity of renal symptoms, which appears to depend on the modification of channel function by the mutant barttin. To date, only a few BSND mutations have been reported, most of which are missense or nonsense mutations. In this study, we report the identification of the first insertion mutation, p.W102Vfs*7, in the BSND gene of a newborn girl with acute clinical symptoms including early-onset chronic renal failure. The results support previous data indicating that mutations that are predicted to abolish barttin expression are associated with a severe phenotype and early onset renal failure.

Identification of Missense Mutation (I12T) in the BSND Gene and Bioinformatics Analysis

Nonsyndromic hearing loss is a paradigm of genetic heterogeneity with 85 loci and 39 nuclear disease genes reported so far. Mutations of BSND have been shown to cause Bartter syndrome type IV, characterized by significant renal abnormalities and deafness and nonsyndromic nearing loss. We studied a Pakistani consanguineous family. Clinical examinations of affected individuals did not reveal the presence of any associated signs, which are hallmarks of the Bartter syndrome type IV. Linkage analysis identified an area of 18.36 Mb shared by all affected individuals between markers D1S2706 and D1S1596. A maximum two-point LOD score of 2.55 with markers D1S2700 and multipoint LOD score of 3.42 with marker D1S1661 were obtained. BSND mutation, that is, p.I12T, cosegregated in all extant members of our pedigree. BSND mutations can cause nonsyndromic hearing loss, and it is a second report for this mutation. The respected protein, that is, BSND, was first modeled, and then, the identified mutation was further analyzed by using different bioinformatics tools; finally, this protein and its mutant was docked with CLCNKB and REN, interactions of BSND, respectively.

Deletion of exons 2–4 in the BSND gene causes severe antenatal Bartter syndrome

BSND gene mutations usually cause severe forms of antenatal Bartter syndrome and sensorineural deafness (SND). Chronic renal failure and transient hypercalciuria are reported as controversial symptoms of this syndrome. All twelve reported BSND mutations cause SND, whereas only two of the mutations give rise to normal glomerular filtration rate (GFR) and two other mutations cause hypercalciuria. The case we report here, where the patient presented with severe clinical symptoms and deletion on exons 2-4 of the BSND gene, has not been reported previously. Decreased GFR, along with hypercalciuria and difficulties in managing fluid and electrolyte requirements, are the reasons why this patient was brought to attention.