Genetic disorders of renal electrolyte transport

Renal antiporter ClC-5 regulates collagen I/IV through the β-catenin pathway and lysosomal degradation

Mutations in Cl-/H+ antiporter ClC-5 cause Dent's disease type 1 (DD1), a rare tubulopathy that progresses to renal fibrosis and kidney failure. Here, we have used DD1 human cellular models and renal tissue from DD1 mice to unravel the role of ClC-5 in renal fibrosis. Our results in cell systems have shown that ClC-5 deletion causes an increase in collagen I (Col I) and IV (Col IV) intracellular levels by promoting their transcription through the β-catenin pathway and impairing their lysosomal-mediated degradation. Increased production of Col I/IV in ClC-5-depleted cells ends up in higher release to the extracellular medium, which may lead to renal fibrosis. Furthermore, our data have revealed that 3-mo-old mice lacking ClC-5 (Clcn5 +/- and Clcn5 -/- ) present higher renal collagen deposition and fibrosis than WT mice. Altogether, we describe a new regulatory mechanism for collagens' production and release by ClC-5, which is altered in DD1 and provides a better understanding of disease progression to renal fibrosis.

[Hydrosodium balance in aging]

One of the kidney's major functions is to adjust the water and sodium balance in order to maintain a state of equilibrium. In the course of aging, even in the absence of renal pathology, changes are observed not only in renal macrostructure (reduction in kidney size, increase in the number of cysts), but also in microstructure (arteriosclerosis, glomerulosclerosis, fibrosis and tubular atrophy). All these changes can disrupt the homeostasis of water and sodium balances. The aim of this article is to review the physiology of water and sodium stores, and to assess the impact of aging on the regulatory loops of these different systems.

Clinical and genetic characteristics of the patients with hypertension and hypokalemia carrying a novel SCNN1A mutation

The objective of this study was to clinically and genetically characterize a pedigree with Liddle syndrome (LS). A LS pedigree comprising with one proband and seven family members was enrolled. The subjects' symptoms, laboratory results and genotypes were analyzed. Peripheral venous samples were collected from the subjects, and genomic DNA was extracted. DNA library construction and exome capture were performed on an Illumina HiSeq 4000 platform. The selected variant sites were validated using Sanger sequencing. The mutation effects were investigated using prediction tools. The proband and her paternal male family members had mild hypertension, hypokalemia and muscle weakness, including the absence of low renin and low aldosterone. Genetic analysis revealed that the proband carried a compound heterozygous mutation in SCNN1A, a novel heterozygous mutation, c.1130T > G (p.Ile377Ser) and a previously characterized polymorphism, c.1987A > G (p.Thr633Ala). The novel mutation site was inherited in an autosomal dominant manner and was predicted by in silico tools to exert a damaging effect. Alterations in the SCNN1A domain were also predicted by protein structure modeling. After six months of follow-up, treatment had significantly improved the patient's limb weakness and electrolyte levels. The novel mutation c.1130T > G of the SCNN1A gene was detected in the pedigree with LS. The clinical manifestations of the pedigree were described, which expand the phenotypic spectrum of LS. This result of this study also emphasizes the value of genetic testing for diagnosing LS.

SCP2 variant is associated with alterations in lipid metabolism, brainstem neurodegeneration, and testicular defects

BACKGROUND

The detoxification of very long-chain and branched-chain fatty acids and the metabolism of cholesterol to form bile acids occur largely through a process called peroxisomal β-oxidation. Mutations in several peroxisomal proteins involved in β-oxidation have been reported, resulting in diseases characterized by neurological defects. The final step of the peroxisomal β-oxidation pathway is catalyzed by sterol carrier protein-x (SCPx), which is encoded by the SCP2 gene. Previously, there have been two reports of SCPx deficiency, which resulted from a homozygous or compound heterozygous SCP2 mutation. We report herein the first patient with a heterozygous SCP2 mutation leading to SCPx deficiency.

RESULTS

Clinical presentations of the patient included progressive brainstem neurodegeneration, cardiac dysrhythmia, muscle wasting, and azoospermia. Plasma fatty acid analysis revealed abnormal values of medium-, long-, and very long-chain fatty acids. Protein expression of SCPx and other enzymes involved in β-oxidation were altered between patient and normal fibroblasts. RNA sequencing and lipidomic analyses identified metabolic pathways that were altered between patient and normal fibroblasts including PPAR signaling, serotonergic signaling, steroid biosynthesis, and fatty acid degradation. Treatment with fenofibrate or 4-hydroxytamoxifen increased SCPx levels, and certain fatty acid levels in patient fibroblasts.

CONCLUSIONS

These findings suggest that the patient's SCP2 mutation resulted in decreased protein levels of SCPx, which may be associated with many metabolic pathways. Increasing SCPx levels through pharmacological interventions may reverse some effects of SCPx deficiency. Collectively, this work provides insight into many of the clinical consequences of SCPx deficiency and provides evidence for potential treatment strategies.

Novel Dent disease 1 cellular models reveal biological processes underlying ClC-5 loss-of-function

Dent disease 1 (DD1) is a rare X-linked renal proximal tubulopathy characterized by low molecular weight proteinuria and variable degree of hypercalciuria, nephrocalcinosis and/or nephrolithiasis, progressing to chronic kidney disease. Although mutations in the electrogenic Cl-/H+ antiporter ClC-5, which impair endocytic uptake in proximal tubule cells, cause the disease, there is poor genotype-phenotype correlation and their contribution to proximal tubule dysfunction remains unclear. To further discover the mechanisms linking ClC-5 loss-of-function to proximal tubule dysfunction, we have generated novel DD1 cellular models depleted of ClC-5 and carrying ClC-5 mutants p.(Val523del), p.(Glu527Asp) and p.(Ile524Lys) using the human proximal tubule-derived RPTEC/TERT1 cell line. Our DD1 cellular models exhibit impaired albumin endocytosis, increased substrate adhesion and decreased collective migration, correlating with a less differentiated epithelial phenotype. Despite sharing functional features, these DD1 cell models exhibit different gene expression profiles, being p.(Val523del) ClC-5 the mutation showing the largest differences. Gene set enrichment analysis pointed to kidney development, anion homeostasis, organic acid transport, extracellular matrix organization and cell-migration biological processes as the most likely involved in DD1 pathophysiology. In conclusion, our results revealed the pathways linking ClC-5 mutations with tubular dysfunction and, importantly, provide new cellular models to further study DD1 pathophysiology.

Association of cystic fibrosis transmembrane conductance regulator with epithelial sodium channel subunits carrying Liddle's syndrome mutations

The association of the cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial sodium channel (ENaC) in the pathophysiology of cystic fibrosis (CF) is controversial. Previously, we demonstrated a close physical association between wild-type (WT) CFTR and WT ENaC. We have also shown that the F508del CFTR fails to associate with ENaC unless the mutant protein is rescued pharmacologically or by low temperature. In this study, we present the evidence for a direct physical association between WT CFTR and ENaC subunits carrying Liddle's syndrome mutations. We show that all three ENaC subunits bearing Liddle's syndrome mutations (both point mutations and the complete truncation of the carboxy terminus), could be coimmunoprecipitated with WT CFTR. The biochemical studies were complemented by fluorescence lifetime imaging microscopy (FLIM), a distance-dependent approach that monitors protein-protein interactions between fluorescently labeled molecules. Our measurements revealed significantly increased fluorescence resonance energy transfer between CFTR and all tested ENaC combinations as compared with controls (ECFP and EYFP cotransfected cells). Our findings are consistent with the notion that CFTR and ENaC are within reach of each other even in the setting of Liddle's syndrome mutations, suggestive of a direct intermolecular interaction between these two proteins.

The contested meanings of race and ethnicity in medical research: A case study of the DynaMed Point of Care tool

Although the use of race and ethnicity for diagnostic purposes remains a controversial practice given the socially contingent meaning of the terms (Bowker and Star, 1999), health researchers continue to report possible relationships between health outcomes and race/ethnicity in the literature. As summaries of these types of studies are incorporated into commercial databases designed to provide medical practitioners with actionable information, there is a risk that the algorithms that drive the databases may unintentionally incorporate racist biases (O'Neil, 2016) in search reports that use race and ethnicity as query terms to identify findings to help in the diagnosis and treatment of particular patients. As a first step to unpacking this risk, we conducted a content analysis of the records and related citation trails in DynaMed's Point of Care (PoC) tool that refer to racial and ethnic research findings. Our analysis demonstrates that DynaMed does not control for how meanings of race and ethnicity are constructed in its entries, does not always accurately represent the nuanced and contingent nature of the findings about race/ethnicity that it cites, and relies on sources that are not always consistent with the 'evidence-based' criterion that the company self-promotes as a feature of its PoC tool. We conclude that, by failing to acknowledge the complex and contradictory ways that race and ethnicity may, or may not, correlate with the risk of a medical ailment, algorithmically-driven tools that use these concepts to establish group risks for medical ailments may unintentionally work to 'resuscitat[e] biological theories of race by modernizing old racial typologies that were based on observations of physical differences with cutting-edge genomic research' (Roberts, 2011: 567).

Gitelman's syndrome with hyperphosphatemia, effectively responding to single oral magnesium oxide administration: A case report

RATIONALE

The Gitelman's syndrome (GS) is characterized by metabolic alkalosis, hypokalemia, hypomagnesemia, and hypocalciuria. However, the involvement of this deranged electrolyte balance in patients with GS in parathyroid hormone action has not been known.

PATIENT CONCERNS

We report a 34-year-old woman with muscle weakness and tetany/seizures caused by electrolyte imbalance. She had hyperphosphatemia and hypocalciuric hypocalcemia in addition to severe hypomagnesemia with low potassium in the absence of metabolic alkalosis. We identified 2 heterozygous mutations in the solute carrier family 12 member 3 gene in this case (c.1732G>A, p.Val578Met and c.2537_38delTT, p.846fs) by targeted sequence for all causative genes of salt-losing tubulopathies.

DIAGNOSES

A diagnosis of GS. Hypocalcemia and hyperphosphatemia were suggested to relate with the secondary obstruction of appropriate parathyroid hormone release following severe hypomagnesemia in GS.

INTERVENTIONS

She was treated with single oral magnesium oxide administration.

OUTCOMES

The electrolyte imbalance including hypocalcemia and hyperphosphatemia were resolved with a remission of clinical manifestations.

LESSONS

These observations, in this case, suggest that even severe hypomagnesemia caused by GS was associated with resistance to appropriate parathyroid hormone secretion. Through this case, we recognize that secondary hypoparathyroidism would be triggered by severe hypomagnesemia in GS.

Gitelman syndrome and primary hyperparathyroidism: a rare association

Gitelman syndrome(GS) is a rare autosomal recessive salt-losing tubulopathy of young adults, characterised by hypokalaemia, hypomagnesaemia, hypocalciuria and secondary hyperaldosteronism. Hypercalcaemia due to hypocalciuria in these patients is extremely rare.A 25-year-old healthy woman was referred to the Endocrinology clinic for evaluation of persistent hypokalaemia. She presented with fatigue, myalgias, cramps and paraesthesia. Her physical examination was normal. Laboratory workup revealed: K⁺ 2.7 mEq/L (r.v.3.5-5.1), 24 hours urinary K⁺ 84.7 mEq/24 hours (r.v.25-125), Mg²⁺ 0.71 mg/dL (r.v.1.6-2.6), 24 hours urinary Mg²⁺ 143.1 mg/24 hours (r.v.73-122), Ca²⁺ 12 mg/dL (r.v.8.4-10.2), aldosterone 47.1 ng/mL (r.v. 4-31) and active renin 374.7 uUI/mL (r.v.4.4-46.1). She was diagnosed with GS and was treated with spironolactone, oral K⁺ and Mg²⁺ supplementation. Further investigation confirmed hypercalcaemia due to primary hyperparathyroidism owing to a single parathyroid adenoma. Following parathyroidectomy serum calcium normalised.Current knowledge favours that hypomagnesaemia in patients with GS protects them from hypercalcaemia. In this context of multiple electrolyte imbalances, correction of hypomagnesaemia is a challenge and should be done carefully. Like in our patient, aetiology of hypercalcaemia should be promptly diagnosed and reversed.

Spectrum of Hypokalemic Paralysis from a Tertiary Care Center in India

Hypokalemic paralysis is an important and reversible cause of acute flaccid paralysis. The treating physician faces unique diagnostic and therapeutic challenges. We did a prospective study and included all patients with acute flaccid weakness and documented serum potassium of <3.5 mEq/L during the period between January 2009 and August 2015. We studied the incidence, etiology, clinical profile, and acid-base disturbances in patients presenting with hypokalemic paralysis and analyzed the significance of periodic and non-periodic forms of hypokalemic paralysis on patient's outcome. Two hundred and six patients were studied with a mean follow-up of 3.6 ± 1.2 years. Mean age was 37.61 ± 2.2 years (range 18-50 years). Males were predominant (M:F ratio 2.1:1). The nonperiodic form of hypokalemic paralysis was the most common (61%). Eighty-one (39%) patients had metabolic acidosis, 78 (38%) had normal acid-base status, and 47 (23%) patients had metabolic alkalosis. The most common secondary cause was distal renal tubular acidosis (RTA) (n = 75, 36%), followed by Gitelman syndrome (n = 39, 18%), thyrotoxic paralysis (n = 8, 4%), hyperaldosteronism (n = 7, 3%), and proximal RTA (n = 6, 4%). Patients with non-periodic paralysis had more urinary loss (40.1 vs. 12.2 mmol, P = 0.04), more requirement of potassium replacement (120 vs. 48 mmol, P = 0.05), and longer recovery time of weakness (48.1 vs. 16.5 h, P = 0.05) than patients with periodic paralysis. Non-periodic form of hypokalemic paralysis was the most common variant in our study. Patients with periodic paralysis had significant incidence of rebound hyperkalemia.

Hypercalcemic Disorders in Children

Hypercalcemia is defined as a serum calcium concentration that is greater than two standard deviations above the normal mean, which in children may vary with age and sex, reflecting changes in the normal physiology at each developmental stage. Hypercalcemic disorders in children may present with hypotonia, poor feeding, vomiting, constipation, abdominal pain, lethargy, polyuria, dehydration, failure to thrive, and seizures. In severe cases renal failure, pancreatitis and reduced consciousness may also occur and older children and adolescents may present with psychiatric symptoms. The causes of hypercalcemia in children can be classified as parathyroid hormone (PTH)-dependent or PTH-independent, and may be congenital or acquired. PTH-independent hypercalcemia, ie, hypercalcemia associated with a suppressed PTH, is commoner in children than PTH-dependent hypercalcemia. Acquired causes of PTH-independent hypercalcemia in children include hypervitaminosis; granulomatous disorders, and endocrinopathies. Congenital syndromes associated with PTH-independent hypercalcemia include idiopathic infantile hypercalcemia (IIH), William's syndrome, and inborn errors of metabolism. PTH-dependent hypercalcemia is usually caused by parathyroid tumors, which may give rise to primary hyperparathyroidism (PHPT) or tertiary hyperparathyroidism, which usually arises in association with chronic renal failure and in the treatment of hypophosphatemic rickets. Acquired causes of PTH-dependent hypercalcemia in neonates include maternal hypocalcemia and extracorporeal membrane oxygenation. PHPT usually occurs as an isolated nonsyndromic and nonhereditary endocrinopathy, but may also occur as a hereditary hypercalcemic disorder such as familial hypocalciuric hypercalcemia, neonatal severe primary hyperparathyroidism, and familial isolated primary hyperparathyroidism, and less commonly, as part of inherited complex syndromic disorders such as multiple endocrine neoplasia (MEN). Advances in identifying the genetic causes have resulted in increased understanding of the underlying biological pathways and improvements in diagnosis. The management of symptomatic hypercalcemia includes interventions such as fluids, antiresorptive medications, and parathyroid surgery. This article presents a clinical, biochemical, and genetic approach to investigating the causes of pediatric hypercalcemia. © 2017 American Society for Bone and Mineral Research.

A Missense Mutation in the Extracellular Domain of αENaC Causes Liddle Syndrome

Liddle syndrome is an autosomal dominant form of hypokalemic hypertension due to mutations in the β- or γ-subunit of the epithelial sodium channel (ENaC). Here, we describe a family with Liddle syndrome due to a mutation in αENaC. The proband was referred because of resistant hypokalemic hypertension, suppressed renin and aldosterone, and no mutations in the genes encoding β- or γENaC. Exome sequencing revealed a heterozygous, nonconservative T>C single-nucleotide mutation in αENaC that substituted Cys479 with Arg (C479R). C479 is a highly conserved residue in the extracellular domain of ENaC and likely involved in a disulfide bridge with the partner cysteine C394. In oocytes, the C479R and C394S mutations resulted in similar twofold increases in amiloride-sensitive ENaC current. Quantification of mature cleaved αENaC in membrane fractions showed that the number of channels did not increase with these mutations. Trypsin, which increases open probability of the channel by proteolytic cleavage, resulted in significantly higher currents in the wild type than in C479R or C394S mutants. In summary, a mutation in the extracellular domain of αENaC causes Liddle syndrome by increasing intrinsic channel activity. This mechanism differs from that of the β- and γ-mutations, which result in an increase in channel density at the cell surface. This mutation may explain other cases of patients with resistant hypertension and also provides novel insight into ENaC activation, which is relevant for kidney sodium reabsorption and salt-sensitive hypertension.

Disease modeling in genetic kidney diseases: mice

The mouse still represents arguably the most important mammal organism in research for modeling human genetic kidney diseases in vivo. Compared with many other mammal species, the breeding and maintenance of mice in the laboratory is relatively simple and cheap and reproduction cycles are short. In addition to classic gene knockout mouse lines, new molecular biological technologies have led to the development of a plethora of other, more sophisticated, mouse models, allowing the targeting of genes or gene function in a cell-specific, tissue-specific and time-dependent fashion. With the refinement of more recently developed genome-editing technologies, including the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system and other engineered nucleases such as zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), our "tool set" of mouse models is expected to rapidly expand. These technological advances hold great promise and should enable us to study and hence understand the biology of inherited kidney diseases in greater detail. By analogy, we may be able to answer questions regarding the impact of individual proteins on the development of human kidney disorders, the underlying mechanisms governing the evolution of the disease and the predicted responsiveness to therapeutic interventions. Moreover, knockout and transgenic mouse models can be highly informative with respect to the effects of genetic variations on renal phenotypes. This review focuses on mouse models that have been devised primarily to study monogenic human kidney diseases, which are typically caused by a single abnormal gene and passed on in a Mendelian pattern. Despite the large number of human hereditary kidney disorders and the multitude of mouse models described in the literature, we attempt to give a balanced overview of several well-known renal pathologies, a few of which are addressed in some detail.

EAST syndrome: Clinical, pathophysiological, and genetic aspects of mutations in KCNJ10

EAST syndrome is a recently described autosomal recessive disorder secondary to mutations in KCNJ10 (Kir4.1), a gene encoding a potassium channel expressed in the brain, eye, ear and kidney. This condition is characterized by 4 cardinal features; Epilepsy, Ataxia, Sensorineural deafness, and (a renal salt-wasting) Tubulopathy, hence the acronym EAST syndrome. Here we review reported clinical manifestations, in particular the neurological signs and symptoms which typically have the most impact on the quality of life of patients. In addition we review the pathophysiology and genetic aspects of the disease. So far 14 different KCNJ10 mutations have been published which either directly affect channel function or may lead to mislocalisation. Investigations of the pathophysiology may provide clues to potential treatments.

Relative roles of principal and intercalated cells in the regulation of sodium balance and blood pressure

The kidney continuously adapts daily renal excretion of NaCl to match dietary intakes in order to maintain the NaCl content of the body, and keep vascular volume constant. Any situation that leads to NaCl retention favors a rise in blood pressure. The aldosterone-sensitive distal nephron, which contains two main types of cells, principal (PC) and intercalated (IC) cells, is an important site for the final regulation of urinary Na(+) excretion. Research over the past 20 years established a paradigm in which PCs are the exclusive site of Na(+) absorption while ICs are solely dedicated to acid-base transport. Recent studies have revealed the unexpected importance of ICs for NaCl reabsorption. Here, we review the mechanisms of Na(+) and Cl(-) transport in the aldosterone-sensitive distal nephron, with emphasis on the role of ICs in maintaining NaCl balance and normal blood pressure.

Clinical and biochemical spectrum of hypokalemic paralysis in North: East India

Background:

Acute hypokalemic paralysis, characterized by acute flaccid paralysis is primarily a calcium channelopathy, but secondary causes like renal tubular acidosis (RTA), thyrotoxic periodic paralysis (TPP), primary hyperaldosteronism, Gitelman’s syndrome are also frequent.

Objective:

To study the etiology, varied presentations, and outcome after therapy of patients with hypokalemic paralysis.

Materials And Methods:

All patients who presented with acute flaccid paralysis with hypokalemia from October 2009 to September 2011 were included in the study. A detailed physical examination and laboratory tests including serum electrolytes, serum creatine phosphokinase (CPK), urine analysis, arterial blood gas analysis, thyroid hormones estimation, and electrocardiogram were carried out. Patients were further investigated for any secondary causes and treated with potassium supplementation.

Result:

The study included 56 patients aged 15-92 years (mean 36.76 ± 13.72), including 15 female patients. Twenty-four patients had hypokalemic paralysis due to secondary cause, which included 4 with distal RTA, 4 with Gitelman syndrome, 3 with TPP, 2 each with hypothyroidism, gastroenteritis, and Liddle’s syndrome, 1 primary hyperaldosteronism, 3 with alcoholism, and 1 with dengue fever. Two female patients were antinuclear antibody-positive. Eleven patient had atypical presentation (neck muscle weakness in 4, bladder involvement in 3, 1 each with finger drop and foot drop, tetany in 1, and calf hypertrophy in 1), and 2 patient had respiratory paralysis. Five patients had positive family history of similar illness. All patients improved dramatically with potassium supplementation.

Conclusion:

A high percentage (42.9%) of secondary cause for hypokalemic paralysis warrants that the underlying cause must be adequately addressed to prevent the persistence or recurrence of paralysis.

The European renal genome project: an integrated approach towards understanding the genetics of kidney development and disease

Rapid progress in genome research creates a wealth of information on the functional annotation of mammalian genome sequences. However, as we accumulate large amounts of scientific information we are facing problems of how to integrate and relate the data produced by various genomic approaches. Here, we propose the novel concept of an organ atlas where diverse data from expression maps to histological findings to mutant phenotypes can be queried, compared and visualized in the context of a three-dimensional reconstruction of the organ. We will seek proof of concept for the organ atlas by elucidating genetic pathways involved in development and pathophysiology of the kidney. Such a kidney atlas may provide a paradigm for a new systems-biology approach in functional genome research aimed at understanding the genetic bases of organ development, physiology and disease.

Licorice abuse: time to send a warning message

Licorice extract has always been recognized as a sweetener and a thirst quencher. Its nutritive value is overrated by many who consume significant amounts and are prone to complications. Glycyrrhetic acid, the active metabolite in licorice, inhibits the enzyme 11-ß-hydroxysteroid dehydrogenase enzyme type 2 with a resultant cortisol-induced mineralocorticoid effect and the tendency towards the elevation of sodium and reduction of potassium levels. This aldosterone-like action is the fundamental basis for understanding its health benefits and the wide spectrum of adverse effects. Herein, we present a comprehensive review of licorice along with the reported complications related to excess intake. Despite its apparent use in a few clinical scenarios, the daily consumption of licorice is never justified because its benefits are minor compared to the adverse outcomes of chronic consumption. The review highlights the importance of investigating the dietary habits and herbal remedies which are being used worldwide on cultural and habitual bases rather than reliable scientific evidence. Licorice is a US Food and Drug Administration (FDA) approved food supplement used in many products without precise regulations to prevent toxicity. Increased awareness among the public is required through TV commercials, newspapers, internet sites, magazines and product labels regarding the upper limit of ingestion and health hazards associated with excess intake. We hope that this review will serve as a warning message that should be transmitted from physicians to patients to avoid excessive licorice intake as well as a message to the FDA to start regulating the use of this substance.

A female adult with Sandifer's syndrome and hiatal hernia misdiagnosed as epilepsy with focal seizures

Sandifer's syndrome is a rare, probably underdiagnosed, and usually pediatric movement disorder associated with gastroesophageal reflux disease. Often, it is misdiagnosed as epilepsy or paroxysmal dyskinesia. We report the case of an adult female with Sandifer's syndrome initially diagnosed as focal epilepsy and treated inefficiently with anticonvulsants for two years.

Pseudohypoparathyroidism presenting with ventricular arrhythmia: a case report

Pseudohypoparathyroidism (PHP) is a rare disorder characterized by varying degrees of unresponsiveness to parathyroid hormone. Patients usually present with hypocalcemia-induced seizures or tetany, whereas no case of hypocalcemia-induced cardiac arrhythmia in PHP has been described to date. In this paper, we report the case of a male adolescent with PHP type 1a who presented with hypocalcemia-induced ventricular extrasystoles (bigeminy, trigeminy) and mild corrected QT interval prolongation. The patient had brachydactyly and his second fingers and toes were longer than the others, a finding consistent with PHP. Laboratory tests detected hypomagnesemia, as well as elevated levels of creatine kinase and lactate dehydrogenase. Ventricular arrhythmia and abnormal laboratory tests improved with calcium supplementation and vitamin D treatment. The findings in this patient suggest that hypomagnesemia may make patients with PHP more susceptible to hypocalcemia and may thus prompt a state of hypocalcemia-induced arrhythmia or other cardiac complications.

Dysfunction of the thick loop of Henle and senescence: from molecular biology to clinical geriatrics

The sodium-potassium-2 chloride bumetanide-sensitive transporter (NKCC2), a protein coded by gene SLC12A1, allows salt reabsorption in the thick ascending loop of Henle (TALH). The functional and clinical exploration of the TALH can be carried out using the Chaimowitz's test, which is based on the exploration of the tubular response to an acute overload of a hypotonic sodium chloride solution. Since this segment is normally responsible for the generation of free water clearance, its function can be assessed via the calculation of such clearance from the parameters obtained during this test. By applying the Chaimowitz's test, the presence of incompetence for sodium reabsorption in TALH in healthy old people was documented. Additionally, it was documented that in water-restricted old rats, a situation that normally induces an increase in the number of NKCC2 in young rats is absent in old ones. In the clinical setting, the increased urinary sodium loss usually found in healthy old people predisposes them to dehydration, hypotension and or hyponatremia when they are on low-sodium diet or under treatment with diuretics. These are commonly found in elderly people with geriatric syndromes such as delirium, gait disorders and incontinence.

CONCLUSION

The NKCC2 transporter decrease in the thick ascending loop of Henle secondary to the ageing could explain the reduced sodium reabsorption of this segment in the healthy elderly and its potential clinical consequences of dehydration and serum sodium abnormalities.

Gitelman syndrome: pathophysiological and clinical aspects

Giltelman syndrome (GS) is a recessive salt-losing tubulopathy of children or young adults caused by a mutation of genes encoding the human sodium chloride cotransporters and magnesium channels in the thiazide-sensitive segments of the distal convoluted tubule. The plasma biochemical picture is characterized by hypokalemia, hypomagnesemia, hypocalciuria, metabolic alkalosis and hypereninemic hyperaldosteronism. However, patients with GS present some clinical and biochemical alterations resembling that observed in thiazide diuretics abuse. On the pathophysiological point of view, GS represents a useful and interesting human model to better understand the clinical consequences of plasma hydro-electrolytes and acid-base derangements, associated with multiple hormonal alterations. The impact of this complex disorder involves cardiovascular, muscle-skeletal and some other physiological functions, adversely affecting the patient's quality of life. This review tries to summarize and better explain the linkage between the electrolytes, neurohormonal derangements and clinical picture. Moreover, the differential diagnosis between other similar electrolyte-induced clinical disorders and GS is also discussed.

A practical approach to genetic hypokalemia

Mutations in genes encoding ion channels, transporters, exchangers, and pumps in human tissues have been increasingly reported to cause hypokalemia. Assessment of history and blood pressure as well as the K⁺ excretion rate and blood acid-base status can help differentiate between acquired and inherited causes of hypokalemia. Familial periodic paralysis, Andersen's syndrome, congenital chloride-losing diarrhea, and cystic fibrosis are genetic causes of hypokalemia with low urine K⁺ excretion. With respect to a high rate of K⁺ excretion associated with faster Na⁺ disorders (mineralocorticoid excess states), glucoricoid-remediable aldosteronism and congenital adrenal hyperplasia due to either 11β-hydroxylase and 17α-hydroxylase deficiencies in the adrenal gland, and Liddle's syndrome and apparent mineralocorticoid excess in the kidney form the genetic causes. Among slow Cl^- disorders (normal blood pressure, low extracellular fluid volume), Bartter's and Gitelman's syndrome are most common with hypochloremic metabolic alkalosis. Renal tubular acidosis caused by mutations in the basolateral Na⁺/HCO₃^- cotransporter (NBC1) in the proximal tubules, apical H⁺-ATPase pump, and basolateral Cl^-/HCO₃^- exchanger (anion exchanger 1, AE1) in the distal tubules and carbonic anhydroase II in both are genetic causes with hyperchloremic metabolic acidosis. Further work on genetic causes of hypokalemia will not only provide a much better understanding of the underlying mechanisms, but also set the stage for development of novel therapies in the future.

Functional modules, mutational load and human genetic disease

The ability to generate a massive amount of sequencing and genotyping data is transforming the study of human genetic disorders. Driven by such innovation, it is likely that whole exome and whole-genome resequencing will replace regionally focused approaches for gene discovery and clinical testing in the next few years. However, this opportunity brings a significant interpretative challenge to assigning function and phenotypic variance to common and rare alleles. Understanding the effect of individual mutations in the context of the remaining genomic variation represents a major challenge to our interpretation of disease. Here, we discuss the challenges of assigning mutation functionality and, drawing from the examples of ciliopathies as well as cohesinopathies and channelopathies, discuss possibilities for the functional modularization of the human genome. Functional modularization in addition to the development of physiologically relevant assays to test allele functionality will accelerate our understanding of disease architecture and enable the use of genome-wide sequence data for disease diagnosis and phenotypic prediction in individuals.

Hereditary renal tubular disorders

The multiple and complex functions of the renal tubule in regulating water, electrolyte, and mineral homeostasis make it prone to numerous genetic abnormalities resulting in malfunction. The phenotypic expression depends on the mode of interference with the normal physiology of the segment affected, and whether the abnormality is caused by loss of function or, less commonly, gain of function. In this review we address the current knowledge about the association between the genetics and clinical manifestations and treatment of representative disorders affecting the length of the nephron.

Effects of thiazide on the expression of TRPV5, calbindin-D28K, and sodium transporters in hypercalciuric rats

TRPV5 is believed to play an important role in the regulation of urinary calcium excretion. We assessed the effects of hydrochlorothiazide (HCTZ) on the expression of TRPV5, calbindin-D(28K), and several sodium transporters in hypercalciuric rats. Sprague-Dawley rats were divided into 4 groups; control, HCTZ, high salt, and high salt with HCTZ group in experiment 1; control, HCTZ, high calcium (Ca), and high Ca with HCTZ group in experiment 2. To quantitate the expression of TRPV5, calbindin-D(28K), and sodium transporters, western blotting was performed. In both experiments, HCTZ significantly decreased urinary calcium excretion. TRPV5 protein abundance decreased in all hypercalciuric rats, and restored by HCTZ in both high salt with HCTZ and high Ca with HCTZ group. Calbindin-D(28K) protein abundance increased in the high salt and high salt with HCTZ groups, but did not differ among groups in experiment 2. Protein abundance of NHE3 and NKCC2 decreased in all hypercalciuric rats, and were restored by HCTZ in only high Ca-induced hypercalciuric rats. In summary, protein abundance of TRPV5, NHE3, and NKCC2 decreased in all hypercalciuric rats. The hypocalciuric effect of HCTZ is associated with increased protein abundance of TRPV5 in high salt or calcium diet-induced hypercalciuric rats.

Phenotype-genotype correlation in antenatal and neonatal variants of Bartter syndrome

BACKGROUND

Ante/neonatal Bartter syndrome (BS) is a hereditary salt-losing tubulopathy due to mutations in genes encoding proteins involved in NaCl reabsorption in the thick ascending limb of Henle's loop. Our aim was to study the frequency, clinical characteristics and outcome of each genetic subtype.

METHODS

Charts of 42 children with mutations in KCNJ1 (n = 19), SLC12A1 (n = 13) CLCNKB (n = 6) or BSND (n = 4) were retrospectively analysed. The median follow-up was 8.3 [0.4-18.0] years.

RESULTS

We describe 24 new mutations: 10 in KCNJ1, 11 in SLC12A1 and 3 in CLCNKB. The onset of polyhydramnios, birth term, height and weight were similar for all groups; three patients had no history of polyhydramnios or premature birth and had CLCNKB mutations according to a less severe renal sodium wasting. Contrasting with these data, patients with CLCNKB had the lowest potassium (P = 0.006 versus KCNJ1 and P = 0.034 versus SLC12A1) and chloride plasma concentrations (P = 0.039 versus KCNJ1 and P = 0.024 versus SLC12A1) and the highest bicarbonataemia (P = 0.026 versus KCNJ1 and P = 0.014 versus SLC12A1). Deafness at diagnosis was constant in patients with BSND mutations; transient neonatal hyperkalaemia was present in two-thirds of the children with KCNJ1 mutations. Nephrocalcinosis was constant in KCNJ1 and SLC12A1 but not in BSND and CLCNKB patients. In most cases, water/electrolyte supplementation + indomethacin led to catch-up growth. Three patients developed chronic renal failure: one with KCNJ1 mutations during the second decade of age and two with CLCNKB and BSND mutations and without nephrocalcinosis during the first year of life.

CONCLUSIONS

We confirmed in a large cohort of ante/ neonatal BS that deafness, transient hyperkalaemia and severe hypokalaemic hypochloraemic alkalosis orientate molecular investigations to BSND, KCNJ1 and CLCNKB genes, respectively. Chronic renal failure is a rare event, associated in this cohort with three genotypes and not always associated with nephrocalcinosis.

Loss of vitamin D receptor produces polyuria by increasing thirst

Vitamin D receptor (VDR)-null mice develop polyuria, but the underlying mechanism remains unknown. In this study, we investigated the relationship between vitamin D and homeostasis of water and electrolytes. VDR-null mice had polyuria, but the urine osmolarity was normal as a result of high salt excretion. The urinary responses to water restriction and to vasopressin were similar between wild-type and VDR-null mice, suggesting intact fluid-handling capacity in VDR-null mice. Compared with wild-type mice, however, renin and angiotensin II were dramatically upregulated in the kidney and brain of VDR-null mice, leading to a marked increase in water intake and salt appetite. Angiotensin II-mediated upregulation of intestinal NHE3 expression partially explained the increased salt absorption and excretion in VDR-null mice. In the brain of VDR-null mice, expression of c-Fos, which is known to associate with increased water intake, was increased in the hypothalamic paraventricular nucleus and the subfornical organ. Treatment with an angiotensin II type 1 receptor antagonist normalized water intake, urinary volume, and c-Fos expression in VDR-null mice. Furthermore, despite a salt-deficient diet to reduce intestinal salt absorption, VDR-null mice still maintained the increased water intake and urinary output. Together, these data indicate that the polyuria observed in VDR-null mice is not caused by impaired renal fluid handling or increased intestinal salt absorption but rather is the result of increased water intake induced by the increase in systemic and brain angiotensin II.

[Inherited monogenic kidney stone diseases: recent diagnostic and therapeutic advances]

Hereditary monogenic kidney stone diseases are rare diseases, since they account for nearly 2% of nephrolithiasis cases in adults and 10% in children. Most of them are severe, because they frequently are associated with nephrocalcinosis and lead to progressive impairment of renal function unless an early and appropriate etiologic treatment is instituted. Unfortunately, treatment is often lacking or started too late since they are often misdiagnosed or overlooked. The present review reports the genotypic and phenotypic characteristics of monogenic nephrolithiases, with special emphasis on the recent advances in the field of diagnosis and therapeutics. Monogenic stone diseases will be classified into three groups according to their mechanism: (1) inborn errors of the metabolism of oxalate (primary hyperoxalurias), uric acid (hereditary hyperuricemias) or other purines (2,8-dihydroxyadeninuria), which, in addition to stone formation, result in crystal deposition in the renal parenchyma; (2) congenital tubulopathies affecting the convoluted proximal tubule (such as Dent's disease, Lowe syndrome or hypophosphatemic rickets), the thick ascending limb of Henlé's loop (such as familial hypomagnesemia and Bartter's syndromes) or the distal past of the nephron (congenital distal tubular acidosis with or without hearing loss), which are frequently associated with nephrocalcinosis, phosphatic stones and extensive tubulointerstitial fibrosis; (3) cystinuria, an isolated defect in tubular reabsorption of cystine and dibasic aminoacids, which results only in the formation of stones but requires a cumbersome treatment. Analysis of stones appears of crucial value for the early diagnosis of these diseases, as in several of them the morphology and composition of stones is specific. In other cases, especially if nephrocalcinosis, phosphatic stones or proteinuria are present, the evaluation of blood and urine chemistry, especially with regard to calcium, phosphate and magnesium, is the key of diagnosis. Search for mutations is now increasingly performed in as much as genetic counselling is important for the detection of heterozygotes in autosomic recessive diseases and of carrier women in X-linked diseases. In conclusion, better awareness to the rare monogenic forms of nephrolithiasis and/or nephrocalcinosis should allow early diagnosis and treatment which are needed to prevent or substantially delay progression of end-stage renal disease. Analysis of every first stone both in children and in adults should never be neglected, in order to early detect unusual forms of nephrolithiasis requiring laboratory evaluation and deep etiologic treatment.

Upregulation of apical sodium-chloride cotransporter and basolateral chloride channels is responsible for the maintenance of salt-sensitive hypertension

We investigated which of the NaCl transporters are involved in the maintenance of salt-sensitive hypertension. Milan hypertensive (MHS) rats were studied 3 mo after birth. In MHS, compared with normotensive strain (MNS), mRNA abundance, quantified by competitive PCR on isolated tubules, was unchanged, both for Na+/H+ isoform 3 (NHE3) and Na+-K+-2Cl- (NKCC2), but higher (119%, n = 5, P < 0.005) for Na+-Cl- (NCC) in distal convoluted tubules (DCT). These results were confirmed by Western blots, which revealed: 1) unchanged NHE3 in the cortex and NKCC2 in the outer medulla; 2) a significant increase (52%, n = 6, P < 0.001) of NCC in the cortex; 3) alpha- and beta-sodium channels [epithelial Na+ channel (ENaC)] unaffected in renal cortex and slightly reduced in the outer medulla, while gamma-ENaC remained unchanged. Pendrin protein expression was unaffected. The role of NCC was reinforced by immunocytochemical studies showing increased NCC on the apical membrane of DCT cells of MHS animals, and by clearance experiments demonstrating a larger sensitivity (P < 0.001) to bendroflumethiazide in MHS rats. Kidney-specific chloride channels (ClC-K) were studied by Western blot experiments on renal cortex and by patch-clamp studies on primary culture of DCT dissected from MNS and MHS animals. Electrophysiological characteristics of ClC-K channels were unchanged in MHS rats, but the number of active channels in a patch was 0.60 +/- 0.21 (n = 35) in MNS rats and 2.17 +/- 0.59 (n = 23) in MHS rats (P < 0.05). The data indicate that, in salt-sensitive hypertension, there is a strong upregulation, both of NCC and ClC-K along the DCT, which explains the persistence of hypertension.

Molecular variants of the thiazide-sensitive Na+-Cl- cotransporter in hypertensive families

BACKGROUND

The thiazide-sensitive Na-Cl cotransporter (TSC) is involved in the fine regulation of sodium excretion by the kidney, and an increase in its activity causes salt-sensitive hypertension and hypercalciuria.

METHODS

To explore the possibility that activating mutations in the TSC gene may be involved in the pathogenesis of primary hypertension, we screened genomic DNA of 68 individuals from hypertensive families of patients with hypercalciuria for variations using single-strand conformation polymorphism and investigated the functional properties using the Xenopus laevis oocyte expression system.

RESULTS

We identified 18 variants in the TSC and, of those, four were nonsynonymous. The A728T, R904Q and R919C variants were introduced into the human TSC cDNA and expressed in Xenopus oocytes to study their effect on Na transport. Although T728 and Q904 did not show any difference in Na uptake, the R919C mutant showed a 60% increase compared to wild-type human TSC and an exaggerated inhibitory action of hydrochlorothiazide. Immunocytochemical analysis revealed no difference in cell surface expression of R919C mutants compared to wild-type hTSC. There was no significant difference in the inhibitory effect of the carboxyl terminus of the serine-threonine kinase WNK4 on the R919C mutant and wild-type hTSC.

CONCLUSIONS

Our results show that the substitution of arginine for cysteine at position 919 of TSC increases Na transport function, and provide support for the hypothesis that mutations in renal tubular sodium transporters may contribute to the development of primary hypertension, a polygenic disorder, by increasing renal sodium reabsorption.

Mechanisms of Disease: what can mouse models tell us about the molecular processes underlying Dent disease?

Two knockout mouse models of Dent disease are similar with regard to the characteristics of Fanconi syndrome, but differ markedly with respect to vitamin D and renal calcium handling. One model exhibits hypercalciuria, renal calcifications and renal failure; the other does not. Data from such experimental models have greatly advanced our understanding of the molecular mechanisms underlying Dent disease. This Review summarizes some of the important phenotypic characteristics shared by mouse models and people with Dent disease. Experimental data are used to predict the molecular mechanisms underlying this disease. Receptor-mediated endocytosis and the mistargeting of megalin, cubilin, the sodium/proton exchanger Nhe3 and the sodium/phosphate transporter Napi-2a will be reviewed, and the causes of mistargeting will be discussed. Kidney stones and renal failure are prominent features of Dent disease. Investigations using a mouse model with nephrocalcinosis and renal failure indicate that citrate therapy delays the onset of these processes in Dent disease. Throughout this Review, questions that might underpin new areas of investigation are proposed.

Function and regulation of epithelial sodium transporters in the kidney of a salt-sensitive hypertensive rat model

OBJECTIVE

To determine the function and regulation of thiazide-sensitive NaCl co-transporters (NCC), NaK2Cl co-transporters (NKCC2), and epithelial sodium channels (ENaC) in the kidneys of a salt-sensitive hypertensive model.

DESIGN AND METHODS

Neonatal Wistar rats were treated with capsaicin or vehicle. Seven-week-old male rats were treated for 2 weeks with: vehicle plus a normal (Con-NS) or high (Con-HS) sodium diet, and capsaicin pretreatment plus a normal (Cap-NS) or high (Cap-HS) sodium diet. Mean arterial pressure (MAP), renal excretory function, and protein expression determined by western blot were performed.

RESULTS

MAP was increased in Cap-HS compared with other groups. Trichlormethiazide increased urine sodium excretion (UNaV) and urine flow rate (UFR) and decreased MAP in Cap-HS rats only. Furosemide increased UNaV and UFR in Cap-NS, Con-HS and Cap-HS, and decreased MAP in Cap-HS rats only. Amiloride had no effect on UNaV, UFR and MAP in any group. Renal NCC contents were increased in Cap-HS compared with Con-NS, Con-HS and Cap-NS rats, and NKCC2 expression was increased in Cap-NS, Con-HS and Cap-HS compared with Con-NS rats. No change was found in ENaC alpha subunit expression. The capsaicin-induced release of calcitonin gene-related peptide from renal tissues was decreased in Cap-HS and Cap-NS compared with Con-HS and Con-NS rats.

CONCLUSION

NCC and possibly NKCC2, but not ENaC, were functionally upregulated in the kidneys of rats subjected to sensory nerve degeneration plus high salt intake, suggesting that sensory neurotransmitters may regulate the expression of the former but not the latter, which may underlie the development of salt-sensitive hypertension in this model.

Cellular magnesium acquisition: an anomaly in embryonic cation homeostasis

The intracellular dominance of magnesium ion makes clinical assessment difficult despite the critical role of Mg(++) in many key functions of cells and enzymes. There is general consensus that serum Mg(++) levels are not representative of the growing number of conditions for which magnesium is known to be important. There is no consensus method or sample source for testing for clinical purposes. High intracellular Mg(++) in vertebrate embryos results in part from interactions of cations which influence cell membrane transport systems. These are functionally competent from the earliest stages, at least transiently held over from the unfertilized ovum. Kinetic studies with radiotracer cations, osmolar variations, media lacking one or more of the four biological cations, Na(+), Mg(++), K(+), and Ca(++), and metabolic poison 0.05 mEq/L NaF, demonstrated that: (1) all four cations influence the behavior of the others, and (2) energy is required for uptake and efflux on different time scales, some against gradient. Na(+) uptake is energy dependent against an efflux gradient. The rate of K(+) loss is equal with or without fluoride, suggesting a lack of an energy requirement at these stages. Ca(++) efflux took twice as long in the presence of fluoride, likely due in part to intracellular binding. Mg(++) is anomalous in that early teleost vertebrate embryos have an intracellular content exceeding the surrounding sea water, an isolated unaffected yolk compartment, and a clear requirement for energy for both uptake and efflux. The physiological, pathological, and therapeutic roles of magnesium are poorly understood. This will change: (1) when (28)Mg is once again generally available at a reasonable cost for both basic research and clinical assessment, and (2) when serum or plasma levels are determined simultaneously with intracellular values, preferably as part of complete four cation profiles. Atomic absorption spectrophotometry, energy-dispersive x-ray analysis, and inductively coupled plasma emission spectroscopy on sublingual mucosal and peripheral blood samples are potential methods of value for coordinated assessments.

Cotransporters, WNKs and hypertension: important leads from the study of monogenetic disorders of blood pressure regulation

Major advances are being made in identifying the structure and behaviour of regulatory cascades that control the activity of cation-Cl(-) cotransporters and certain Na(+), K(+) and Cl(-) channels. These transporters play key roles in regulating arterial blood pressure as they are not only responsible for NaCl reabsorption in the thick ascending limb and distal tubule of the kidney, but are also involved in regulating smooth muscle Ca(2+) levels. It is now apparent that defects in these transporters, and particularly in the regulatory cascades, cause some monogenetic forms of hypertension and may contribute to essential hypertension and problems with K(+) homoeostasis. Two families of kinases are prominent in these processes: the Ste-20-related kinases [OSR1 (oxidative stress-responsive kinase 1) and SPAK (Ste20/SPS1-related proline/alanine-rich kinase)] and the WNKs [with no lysine kinases]. These kinases affect the behaviour of their targets through both phosphorylation and by acting as scaffolding proteins, bringing together regulatory complexes. This review analyses how these kinases affect transport by activating or inhibiting individual transporters at the cell surface, or by changing the surface density of transporters by altering the rate of insertion or removal of transporters from the cell surface, and perhaps through controlling the rate of transporter degradation. This new knowledge should not only help us target antihypertensive therapy more appropriately, but could also provide the basis for developing new therapeutic approaches to essential hypertension.

Sodium transporters in the distal nephron and disease implications

The post-macula densa segments of the renal tubule--that is, the distal convoluted tubule, connecting tubule, and collecting duct--play a central role in determining final urine sodium excretion. The major regulated sodium transporters and channels in these cell types include the thiazide-sensitive (Na-Cl) cotransporter (NCC), the epithelial sodium channel (ENaC), and Na-K-ATPase. Furthermore, although not involved in sodium reabsorption, the anion exchanger, pendrin, and the basolateral bumetanide-sensitive Na-K-2Cl cotransporter (NKCC1 or BSC2) have roles in blood-volume maintenance. Mutations in several of these major sodium transporters, channel subunits, and their regulatory proteins have been linked to human diseases such as Liddle's syndrome, Gitelman's syndrome, and Gordon's syndrome, emphasizing the need for appropriate regulation of sodium at these sites for maintenance of sodium balance and normotension.

Cytochrome P450 enzymes: Central players in cardiovascular health and disease

Cardiovascular disease (CVD) is a human health crisis that remains the leading cause of death worldwide. The cytochrome P450 (CYP) class of enzymes are key metabolizers of both xenobiotics and endobiotics. Many CYP enzyme families have been identified in the heart, endothelium and smooth muscle of blood vessels. Furthermore, mounting evidence points to the role of endogenous CYP metabolites, such as epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraenoic acids (HETEs), prostacyclin (PGI(2)), aldosterone, and sex hormones, in the maintenance of cardiovascular health. Emerging science and the development of genetic screening have provided us with information on the differences in CYP expression among populations and groups of individuals. With this information, a link between CYP expression and activity and CVD, such as hypertension, coronary artery disease (CAD), myocardial infarction, heart failure, stroke, and cardiomyopathy and arrhythmias, has been established. In fact many currently used therapeutic modalities in CVD owe their therapeutic efficacy to their effect on CYP metabolites. Thus, the evidence for the involvement of CYP in CVD is numerous. Concentrating on treatment modalities that target the CYP pathway makes ethical sense for the affected individuals and decreases the socioeconomic burden of this disease. However, more research is needed to allow the integration of this information into a clinical setting.

Inherited Renal Tubulopathies Associated With Metabolic Alkalosis: Effects on Blood Pressure

Inherited tubular disorders associated with metabolic alkalosis are caused by several gene mutations encoding different tubular transporters responsible for NaCl renal handling. Body volume and renin-angiotensin-aldosterone system status are determined by NaCl reabsorption in the distal nephron. Two common hallmarks in affected individuals: hypokalemia and normal / high blood pressure, support the differential diagnosis. Bartter's syndrome, characterized by hypokalemia and normal blood pressure, is a heterogenic disease caused by the loss of function of SLC12A1 (type 1), KCNJ1 (type 2), CLCNKB (type 3), or BSND genes (type 4). As a result, patients present with renal salt wasting and hypercalciuria. Gitelman's syndrome is caused by the loss of funcion of the SLC12A3 gene and may resemble Bartter's syndrome, though is associated with the very low urinary calcium. Liddle's syndrome, also with similar phenotype but with hypertension, is produced by the gain of function of the SNCC1B or SNCC1G genes, and must be distinguished from other entities of inherited hypertension such as Apparently Mineralocorticoid Excess, of glucocorticoid remediable hypertension.

The loss of the chloride channel, ClC-5, delays apical iodide efflux and induces a euthyroid goiter in the mouse thyroid gland

Genetic inactivation of ClC-5, a voltage-gated chloride channel prominently expressed in the kidney, leads to proteinuria because of defective apical endocytosis in proximal tubular cells. Because thyroid hormone secretion depends on apical endocytosis of thyroglobulin (Tg), we investigated whether ClC-5 is expressed in the thyroid and affects its function, using Clcn5-deficient knockout (KO) mice. We found that ClC-5 is highly expressed in wild-type mouse thyroid ( approximately 40% of mRNA kidney level). The protein was immunolocalized at the apical pole of thyrocytes. In Percoll gradients, ClC-5 overlapped with plasma membrane and early endosome markers, but best codistributed with the late endosomal marker, Rab7. ClC-5 KO mice were euthyroid (normal T4 and TSH serum levels) but developed a goiter with parallel iodine and Tg accumulation (i.e. normal Tg iodination level). When comparing ClC-5 KO with wild-type mice, thyroid 125I uptake after 1 h was doubled, incorporation into Tg was decreased by approximately 2-fold, so that trichloroacetic acid-soluble 125I increased approximately 4-fold. Enhanced 125I- efflux upon perchlorate and presence of 125I-Tg as autoradiographic rings at follicle periphery demonstrated delayed iodide organification. Endocytic trafficking of 125I-Tg toward lysosomes was not inhibited. Expression of pendrin, an I-/Cl- exchanger involved in apical iodide efflux, was selectively decreased by 60% in KO mice at mRNA and protein levels. Thus, ClC-5 is well expressed in the thyroid but is not critical for apical endocytosis, contrary to the kidney. Instead, the goiter associated with ClC-5 KO results from impaired rate of apical iodide efflux by down-regulation of pendrin expression.

Channels, carriers, and pumps in the pathogenesis of sodium-sensitive hypertension

Sodium-sensitive hypertension is thought to be dependent on primary alterations in renal tubular sodium reabsorption. The major apical plasma membrane Na(+) transporters include the proximal tubular Na(+)-H(+) exchanger, the thick ascending limb Na(+)-K(+)-2Cl(-) cotransport system, the distal tubular Na(+)-Cl(-) cotransporter, and the collecting duct epithelial sodium channel (ENaC). This article explores the role of each transporter in the pathogenesis of hypertension. Although the contribution of the proximal tubule Na(+)-H(+) exchanger is not yet defined completely, more convincing data have been generated about the importance of the Na(+)-K(+)-2Cl(-). Indeed at least 2 forms of hypertension appear to be related to the up-regulation of the transporter: the so-called programmed hypertension induced by low-protein diet during pregnancy and the early phase of hypertension in the Milan strain of rats. With respect to the Na(+)-Cl(-) cotransporter this may be overactive caused by inactivating mutation of WNK4 as in the Gordon syndrome, although it is the main actor for the maintenance phase of the hypertension found in the Milan strain of rats. Finally, the contribution of the ENaC has been established clearly; indeed, in the Liddle syndrome the mutation of the ENaC gene leads to a longer retention of the channel on the cell surface of collecting duct principal cells, thus inducing stronger sodium reabsorption along this segment. All these examples clearly indicate that renal sodium transporters may be responsible for various types of sodium-sensitive hypertension.

Genetic Analysis of Gitelman Syndrome Patients from the Czech Republic and Slovakia – Three Novel Mutations Found

<i>Background:</i> To investigate the genetic cause of inherited hypokalemic metabolic alkalosis associated with Gitelman’s syndrome, we searched for mutations in the SLC12A3 gene (thiazide-sensitive NaCl cotransporter) among a set of patients from the Czech Republic and Slovakia. <i>Methods:</i> We collected blood samples of patients from 16 families with characteristic clinical features. DNA was analyzed for mutation detection with SSCP and subsequent sequencing. Several mutations might be missed when only the SSCP method is applied, therefore direct sequencing of all the 26 exons became an essential tool. <i>Results:</i> Genetic analysis revealed mainly missense mutations. Two novel mutations, c.480dupC (p.Pro160fsX97) and c.238dupCC (p. Pro79fsX35), caused a frameshift and preliminary stop codon appearance. Missense mutation c.790 G → C (p.Gly264Arg) has never been reported before. Mutation c.1315G → A (p.Gly439Ser) was frequent among our collection of unrelated patients (5 out of 16). Homozygous Gly439Ser was observed in a patient with chondrocalcinosis. <i>Conclusion:</i> We identified 13 different causative mutations in a cohort of Gitelman syndrome patients. Three of those mutations are novel. The occurrence of two mutation detections per individual corresponding to a recessive trait of inheritance was 62.5%. Gly439Ser is the most frequent type of mutation among our patients. Statistic evaluation of genotype/phenotype correlation could not be carried out.

Metabolic Bone Disease in Children

Metabolic bone disease in children includes many hereditary and acquired conditions of diverse etiology that lead to disturbed metabolism of the bone tissue. Some of these processes primarily affect bone; others are secondary to nutritional deficiencies, a variety of chronic disorders, and/or treatment with some drugs. Some of these disorders are rare, but some present public health concerns (for instance, rickets) that have been well known for many years but still persist. The most important clinical consequences of bone metabolic diseases in the pediatric population include reduced linear growth, bone deformations, and non-traumatic fractures leading to bone pain, deterioration of motor development and disability. In this article, we analyze primary and secondary osteoporosis, rickets, osteomalacia (nutritional and hereditary vitamin D-dependent, hypophosphatemic and that due to renal tubular abnormalities), renal osteodystrophy, sclerosing bony disorders, and some genetic bone diseases (hypophosphatasia, fibrous dysplasia, skeletal dysplasia, juvenile Paget disease, familial expansile osteolysis, and osteoporosis pseudoglioma syndrome). Early identification and treatment of potential risk factors is essential for skeletal health in adulthood. In most conditions it is necessary to ensure an appropriate diet, with calcium and vitamin D, and an adequate amount of physical activity as a means of prevention. In secondary bone diseases, treatment of the primary disorder is crucial. Most genetic disorders await prospective gene therapies, while bone marrow transplantation has been attempted in other disorders. At present, affected patients are treated symptomatically, frequently by interdisciplinary teams. The role of exercise and pharmacologic therapy with calcium, vitamin D, phosphate, bisphosphonates, calcitonin, sex hormones, growth hormone, and thiazides is discussed. The perspectives on future therapy with insulin-like growth factor-1, new analogs of vitamin D, strontium, osteoprotegerin, and calcimimetics are presented.