Renal Tubulopathy Research Articles

Research Article A novel homozygous stop gain mutation in SLC12A3 gene cause Gitelman syndrome in Saudi consanguineous family

Gitelman syndrome (GS) is a genetic disorder that affects kidney and causes an imbalance of charged atoms (ions) in the body, including ions of potassium, magnesium, and calcium. GS is characterized by hypokalemia and metabolic alkalosis. GS is a rare autosomal recessive renal tubulopathy disease caused by loss-of-function mutations in the SLC12A3 gene. Objective of the present study is to find the genetic causes involved in a consanguineous Saudi family. Whole exome sequencing was done to find out the genetic mutation in the affected members of the family and the putative mutation was further validated by subsequent Sanger sequencing in other member of the family. We identified a novel homozygous mutation c.2686C>T as a result in p.Arg896* stop gained in exon 23 of SLC12A3 gene. The mutation was ruled out in 100 unrelated healthy controls. A novel homozygous stop gain mutation detected in this study has not yet been reported as pathogenic in literature or variant databases. Functional prediction of this mutation was performed using various online in silico prediction tools and all predicted it be disease causing. In conclusion, the here detected homozygous SLC12A3 mutation in the SLC12A3 gene as a result a truncated protein produced with a premature stop gain would expected to lead to functional loss to cause GS in Saudi family. This study will add more knowledge about GS in Arab populations’ database of genetic disorders and will help in the genetic counselling of the families in Saudi Arabia.

Phenotypic and Genotypic Heterogeneity of RRM2B Variants.

Genotype and phenotype of RRM2B mutation have become increasingly heterogeneous. This review aims at summarizing recent advances concerning the genotypic and phenotypic variability of RRM2B mutations. The review evaluated clinical and instrumental data of 82 patients carrying a mutation in the RRM2B gene reported in 18 publications with regard to onset, frequency, and type of clinical manifestations and genetic findings. The review showed marked variety of clinical manifestations and marked variety of age at onset. Organs predominantly affected in RRM2B mutation carriers are the skeletal muscle, the brain, and the kidneys. Additionally affected may be the eyes, ears, endocrine organs, heart, gastro-intestinal tract, bone marrow, or the peripheral nerves. So far 43 mutations in 81 patients have been reported. Diagnosing RRM2B-associated disease requires demonstration of an appropriate phenotype and a RRM2B mutation. Various clinical manifestations are accessible to various invasive or noninvasive therapeutic measures. The outcome of RRM2B-associated mitochondrial disorders is highly variable ranging from early death to survival into adulthood. Phenotype and genotype in RRM2B mutation carriers are more widespread than anticipated. Particularly in patients with chronic progressive external ophthalmoplegia, ptosis, limb muscle weakness, muscle hypotonia, renal tubulopathy, ataxia, deafness, and lactic acidosis, a RRM2B mutation should be considered.

Salt-Losing Tubulopathies in Children: What's New, What's Controversial?

Renal tubulopathies provide insights into the inner workings of the kidney, yet also pose therapeutic challenges. Because of the central nature of sodium in tubular transport physiology, disorders of sodium handling may affect virtually all aspects of the homeostatic functions of the kidney. Yet, owing to the rarity of these disorders, little clinical evidence regarding treatment exists. Consequently, treatment can vary widely between individual physicians and centers and is based mainly on understanding of renal physiology, reported clinical observations, and individual experiences. Salt-losing tubulopathies can affect all tubular segments, from the proximal tubule to the collecting duct. But the more frequently observed disorders are Bartter and Gitelman syndrome, which affect salt transport in the thick ascending limb of Henle's loop and/or the distal convoluted tubule, and these disorders generate the greatest controversies regarding management. Here, we review clinical and molecular aspects of salt-losing tubulopathies and discuss novel insights provided mainly by genetic investigations and retrospective clinical reviews. Additionally, we discuss controversial topics in the management of these disorders to highlight areas of importance for future clinical trials. International collaboration will be required to perform clinical studies to inform the treatment of these rare disorders.

Phase 3 Randomized, Controlled Trial of Switching to Fixed-dose Bictegravir/Emtricitabine/Tenofovir Alafenamide (B/F/TAF) from Boosted Protease Inhibitor-based Regimens in Virologically Suppressed Adults: Week 48 Results

BackgroundBoosted protease inhibitor regimens (bPIs) are effective and often used in HIV-infected individuals with difficulties with adherence, but they can have drug–drug interactions and GI adverse effects. Bictegravir (B), a novel, potent integrase strand transfer inhibitor with a high barrier to resistance and low potential for drug–drug interactions, was coformulated with the recommended nucleoside reverse transcriptase inhibitor backbone emtricitabine (FTC)/tenofovir alafenamide (F/TAF) and demonstrated high efficacy and tolerability in randomized studies in treatment-naïve adults. This randomized Phase 3 study assesses efficacy and safety of switching to B/F/TAF from a multi-tablet regimen containing a bPI.MethodsHIV-infected adults suppressed on regimens of boosted atazanavir (ATV) or darunavir (DRV) + abacavir/lamivudine (ABC/3TC) or FTC/tenofovir disoproxil fumarate (TDF) were randomized 1:1 to continue their current bPI regimen or switch to open-label coformulated B/F/TAF (50/200/25 mg) once daily. Primary endpoint was proportion with HIV-1 RNA ≥50 copies/mL (c/mL) at W48 (FDA snapshot). Noninferiority was assessed through 95.002% confidence intervals (CI) using a margin of 4%. Secondary endpoints included proportion with HIV-1 RNA <50 c/mL and safety measures at W48.ResultsA total of 577 participants were randomized and treated with B/F/TAF (n = 290) or current bPI regimens (n = 287): 17% women, 26% Black, median age 48 years. Most were receiving a bPI with FTC/TDF (85%) at screening. At W48, switching to B/F/TAF was noninferior to continuing bPI with 1.7% in each group having HIV-1 RNA ≥50 c/mL (difference −0.0%; 95.002% CI −2.5% to 2.5%, P = 1.00); the proportion with HIV-1 RNA <50 c/mL was 92.1% in B/F/TAF vs. 88.9% in bPI. No participant on B/F/TAF developed resistance to study drugs. One participant on DRV/ritonavir + ABC/3TC developed a treatment-emergent L74V mutation. Incidence of grade 3 or 4 AEs was similar (B/F/TAF 4%, bPI regimens 6%). No renal discontinuations or tubulopathy cases occurred with B/F/TAF.ConclusionAdults switching to B/F/TAF from a boosted PI maintained high rates of virologic suppression without resistance. B/F/TAF was safe and well tolerated.Disclosures E. Daar, Bristol-Myers Squibb: Consultant, Consulting fee. Gilead Sciences, Inc.: Consultant, Grant Investigator and Scientific Advisor, Consulting fee and Research support. Janssen: Consultant, Grant Investigator and Scientific Advisor, Consulting fee and Research support. Merck: Consultant, Grant Investigator and Scientific Advisor, Consulting fee and Research support. Teva Pharmaceuticals: Consultant and Scientific Advisor, Consulting fee. ViiV: Consultant, Grant Investigator and Scientific Advisor, Consulting fee and Research support. E. DeJesus, Abbott Laboratories; Achillion Pharmaceuticals, Avexa, Boehringer Ingelheim, Bristol-Myers Squibb, Gilead Sciences, GlaxoSmithKline, Hoffmann LaRoche, Idenix, Janssen, Merck, Pfizer, Sangamo, Taimed, Tobira, and Vertex: Grant Investigator, Research grant. Bristol-Myers Squibb, Gilead Sciences, Janssen, Merck, and Vertex: Scientific Advisor, Consulting fee. P. Ruane, Gilead: Investigator, Scientific Advisor and Shareholder, Consulting fee and Research support. Merck: Speaker’s Bureau, Speaker honorarium. Boehringer: Investigator, Scientific Advisor and Speaker’s Bureau, Consulting fee, Research support and Speaker honorarium. Janssen: Investigator, Scientific Advisor and Speaker’s Bureau, Consulting fee, Research support and Speaker honorarium. Abbott: Investigator, Scientific Advisor and Speaker’s Bureau, Research support and Speaker honorarium. Idenix: Investigator, Research support. ViiV: Scientific Advisor and Speaker’s Bureau, Consulting fee and Speaker honorarium. BMS: Consultant, Investigator and Speaker’s Bureau, Consulting fee, Research support and Speaker honorarium. G. Crofoot, Gilead: Investigator and Scientific Advisor, Advisory honorarium and Research grant. ViiV: Investigator and Scientific Advisor, Advisory honorarium, Research grant and Research support. C. Creticos, Thera Technologies and ViiV Healthcare: Scientific Advisor, Consulting fee. Gilead sciences, Merck, and ViiV Healthcare: Investigator, Research support. Pfizer: Speaker’s Bureau, Speaker honorarium. J. K. Rockstroh, Abbvie: Consultant and Investigator, Consulting fee and Speaker honorarium. Gilead: Consultant, Investigator and Scientific Advisor, Consulting fee and Speaker honorarium. ViiV: Scientific Advisor, Consulting fee. Janssen: Investigator and Speaker at educational event, Speaker honorarium. J. M. Molina, Gilead, ViiV, Merck, Janssen, BMS and TEVA: Scientific Advisor, Speaker honorarium. Y. P. Liu, Gilead: Employee and Shareholder, Salary and Shareholder. K. Andreatta, Gilead: Employee and Shareholder, Salary and Shareholder. H. Graham, Gilead Sciences: Employee and Shareholder, Salary. A. Cheng, Gilead: Employee and Shareholder, Salary. H. Martin, Gilead Sciences: Employee, Salary. E. Quirk, Gilead: Employee and Shareholder, Salary

Efficacy and Safety of Tenofovir Alafenamide vs. Tenofovir Disoproxil Fumarate in HIV-infected, Virologically Suppressed Black and Non-Blacks Adults Through Week 96: Subgroup Analysis of a Randomized Switch Study

BackgroundBlack adults are disproportionately affected by HIV.MethodsWe conducted a 96-week subgroup analysis by race (Black vs. non-Black) for efficacy (pre-specified) and safety (post-hoc) from a randomized, double blind, active-controlled study in virologically suppressed HIV-infected individuals who switched to emtricitabine/tenofovir alafenamide (FTC/TAF) from FTC/tenofovir disoproxil fumarate (FTC/TDF) vs. continuing FTC/TDF while remaining on the same third agent.ResultsOf 663 treated patients, 136 (20.5%) self-identified as Black (FTC /TAF n = 69, FTC /TDF n = 67). Baseline viral load, CD4 counts, renal laboratory parameters, and bone mineral density (BMD) were similar between the two arms within Blacks and non-Blacks. For Blacks, virologic success by FDA snapshot algorithm at week 96: FTC /TAF 87.0% vs. FTC /TDF 88.1%; for non-Blacks 89.0% vs. 89.7%. Few participants discontinued study drug due to adverse events in either subgroups (FTC/TAF vs. FTC/TDF: Black 0 vs.. 1.5%; non-Black, 3.0% vs. 1.1%). In assessment of renal and bone safety using estimated glomerular filtration rate (eGFR), renal biomarkers, and BMD, there were differences between two arms that generally favored FTC/TAF over FTC/TDF (Table). In the overall population, no cases of Fanconi syndrome or proximal renal tubulopathy occurred with FTC/TAF; one FTC/TDF participant discontinued study drug due to proximal tubulopathy.ConclusionIn virologically suppressed Black adults, FTC/TAF demonstrated improvements in renal and bone safety over FTC/TDF with similar sustained efficacy at week 96. These results support switching to FTC/TAF from FTC/TDF for the treatment of HIV-1 infection in Black adults.Disclosures J. A. Flamm, Gilead: Investigator, Research support; T. Vanig, Gilead: Consultant, Investigator and Speaker’s Bureau, Consulting fee, Research support and Speaker honorarium; J. Gathe, Gilead: Investigator, Research support; C. Kinder, Gilead: Investigator, Research support; M. Para, Gilead: Investigator, Research grant and Research support; B. Rashbaum, Gilead: Investigator and Shareholder, Research support and Speaker honorarium; S. Segal-Maurer, Gilead Sciences: Consultant, Investigator, Scientific Advisor and Speaker’s Bureau, Consulting fee, Research support and Speaker honorarium; Janssen Therapeutics: Speaker’s Bureau, Speaker honorarium; D. Shamblaw, Gilead: Investigator, Research support; M. Wohlfeiler, Gilead: Investigator, Research support; B. Young, Gilead Sciences: Independent Contractor, Investigator, Research Contractor and Scientific Advisor, Consulting fee, Research support and Speaker honorarium; Merck & Co: Scientific Advisor and Speaker’s Bureau, Consulting fee, Research support and Speaker honorarium; ViiV Healthcare: Scientific Advisor, Research grant; C. Zurawski, Gilead: Investigator, Research grant; M. S. Rhee, Gilead: Employee and Shareholder, Salary

Expert consensus for the diagnosis and treatment of patients with Gitelman syndrome

Gitelman syndrome (GS) is an autosomal recessive, salt-losing tubulopathy caused by inactivating mutations in the SLC12A3 gene that encodes the thiazide-sensitive sodium-chloride cotransporter (NCC). GS is characterized by hypokalemic metabolic alkalosis, hypomagnesemia and hypocalciuria. GS is one of the most common inherited renal tubulopathy with a prevalence estimated at about one to ten per 40 000 people. The prevalence of GS is even higher in Asia than other countries. The majority of GS patients present mild and nonspecific symptoms during adolescence or adulthood. Common clinical manifestations are associated with electrolyte abnormalities, such as muscle weakness, salt craving and tetany. However, the phenotype of GS is highly variable and links to the quality of life. Diagnosis of GS is based on the clinical symptoms, biochemical abnormalities (normal/low blood pressure, metabolic alkalosis, hypomagnesemia, hypocalciuria and increased activity of renin-angiotensin- aldosterone system) and genetic test. Genetic diagnosis of GS is recommended for all patients and the diagnosis is confirmed when biallelic inactivating SLC12A3 mutations are identified. The differential diagnosis includes renal tubular acidosis, primary hyperaldosteronism, Bartter syndrome, Liddle syndrome and other diseases that cause hypokalemia. Among them Bartter syndrome (especially type Ⅲ) is the most important genetic disorder to consider due to its similar manifestations with GS. All GS patients are encouraged to keep high-sodium diet. Magnesium and potassium supplements (oral or intravenous) are usually given to GS patients to improve clinical symptoms. Other medicines such as aldosterone receptor antagonists, angiotensin-converting-enzyme inhibitors (ACEIs), angiotensin Ⅱ receptor blockers (ARBs) and prostaglandin synthetase inhibitors (PGSIs) are alternative choices of treating hypokalemia, but the side-effects of these medication should be well considered. Management of GS includes health education, complication evaluation and regular follow-up. Annual evaluation by a nephrologist is recommended. Extra evaluation and treatment depend on special conditions, such as pregnancy, perioperative or growth period. Antenatal diagnosis for GS is technically feasible but not recommend due to the benign prognosis in the majority of patients. In general, this expert consensus statement aims to establish an initial framework for the better diagnosis, treatment and management of Chinese patients with GS.

Inherited, not acquired, Gitelman syndrome in a patient with Sj\xf6gren\u2019s syndrome: importance of genetic testing to distinguish the two forms

Gitelman syndrome (GS) is an autosomal recessive, salt-losing renal tubulopathy caused by mutations in the SLC12A3 gene; however, it can also be acquired in patients with autoimmune disease, especially in those with Sjögren’s syndrome. Differentiating between the inherited and acquired forms of GS is clinically difficult. We report a case of inherited, not acquired, GS in a patient with Sjögren’s syndrome. A 41-year-old woman, who had been diagnosed with Sjögren’s syndrome at 27-years-old, had shown chronic hypokalemia (2.5–3.5 mmol/L). Laboratory tests showed hypokalemic alkalosis, hypomagnesemia, and hypocalciuria, corresponding to GS. Although acquired GS associated with Sjögren’s syndrome was initially suspected, a genetic test identified a novel homozygous mutation of c.1336-2A > T in the SLC12A3 gene, which resulted in aberrant splicing in the SLC12A3 transcript with the exclusion of exons 11 and 12. Thus, the GS was diagnosed as not the acquired but the inherited form. In the diagnosis of GS in patients with autoimmune disease, genetic testing of SLC12A3 is essential for differentiating the two forms.

Increased urinary prostaglandin E2 metabolite: A potential therapeutic target of Gitelman syndrome.

BackgroundGitelman syndrome (GS), an inherited autosomal recessive salt-losing renal tubulopathy caused by mutations in SLC12A3 gene, has been associated with normal prostaglandin E2 (PGE2) levels since 1995 by a study involving 11 clinically diagnosed patients. However, it is difficult to explain why cyclooxygenase-2 (COX2) inhibitors, which pharmacologically reduce PGE2 synthesis, are helpful to patients with GS, and few studies performed in the last 20 years have measured PGE2 levels. The relationships between the clinical manifestations and PGE2 levels were never thoroughly analyzed.MethodsThis study involved 39 GS patients diagnosed by SLC12A3 gene sequencing. Plasma and 24-h urine samples as well as the clinical data were collected at admission. PGE2 and PGEM levels were detected in plasma and urine samples by enzyme immunoassays. The in vivo function of the sodium-chloride co-transporter (NCC) in GS patients was evaluated using a modified thiazide test. The association among PGE2 levels, clinical manifestations and the function of NCC in GS patients were analyzed.ResultsSignificantly higher levels of urinary and plasma PGEM were observed in GS patients than in the healthy volunteers. Higher urinary PGEM levels indicated more severe clinical manifestations and NCC dysfunction estimated by the increase of Cl- clearance. A higher PGEM level was found in male GS patients, who showed earlier onset age and more severe hypokalemia, hypochloremia and metabolic alkalosis than female GS patients. No relationship between renin angiotensin aldosterone system activation and PGEM level was observed.ConclusionsHigher urinary PGEM levels indicated more severe clinical manifestations and NCC dysfunction in GS patients. COX2 inhibition might be a potential therapeutic target in GS patients with elevated PGEM levels.

Renal Injury and Dysfunction among HIV Positive Patients Receiving Tenofovir Based Anti-Retroviral Therapy

The rate of renal disease among patients with HIV has decreased significantly since the introduction of highly active antiretroviral therapy (HAART). Patients receiving tenofovir, disoproxil, fumarate (TDF) had an increased prevalence of proximal renal tubular dysfunction and injury but its clinical significance remain controversial. To difine the renal tubulopathy injury among patients with HIV with and without TDF. A cross-sectional study was conducted among HIV positive patients receiving TDF (N= 176) and non TDF regimen (N= 146) at outpatient clinic. All patients were evaluated regarding serum creatinine, electrolytes, phosphate and differing urinary parameters (proteinuria, glycosuria and pyuria). Estimated glomerular filtration rate (GFR) was calculated using CKD-EPI equation. Of 322 participants with mean age of 41.6+-11.4 years and HIV duration of 7.2+-4.3 years, the TDF and non TDF groups were similar on most clinical and demographic factors. GFR was 100.6+- 17.8 mL/min/1.73 m2 in TDF group and 97.5+- 19.6 mL/min/1.73 m2 in non-TDF group (p= 0.143). During evaluation, 3.4% of TDF patients vs. none of the non TDF-patients had hypophosphataemia (&lt; 2.5 mg/dL), 3.9% of TDF-patients vs. 1.3% of non TDF had hypokalemia (&lt; 3.5 mg/dL), and 0.68% of TDF-patients vs. none of non TDF patients had acidosis (&lt; 18 mEq/L) with no statistically significant difference between groups. The proportion of patients with evidence of urine abnormalities was also similar in the two groups (Dipstick proteinuria &gt; 1+, TDF: 17.6% vs. non-TDF 20.5%, p= 0.568, and pyuria; TDF: 27.3% vs. non TDF 20.5%, p= 0.192). Renal impairment, electrolyte disturbances and renal tubulopathy were uncommon among HIV positive patients receiving TDF-based antiretroviral therapy and did not significantly differ between TDF and non TDF regimens

P075 Efficacy and safety of switching to EVG/COBI/FTC/TAF in virologically suppressed women

IntroductionElvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate(E/C/F/TDF) demonstrated superior efficacy when compared with atazanavir boosted by ritonavir(ATV/r+F/TDF) in 575 treatment naïve women at Week(W) 48. We now report the safety and efficacy of subsequent switching to E/C/F/tenofovir alafenamide(TAF) versus remaining on ATV/r+F/TDF.MethodsAfter completing the initial randomised, blinded 48-week trial,women on ATV/r+F/TDF were randomised 3:1 to receive open label E/C/F/TAF versus remaining on their current regimen. Viral suppression by FDA snapshot analysis, pre-defined bone and renal safety and tolerability endpoints 48 weeks after switch are reported. Women who become pregnant while on study are given the option to continue study drug.Results212 HIV-infected, virologically suppressed women were randomised(E/C/F/TAF n=159, ATV/r+F/TDF n=53). Virologic suppression(&lt;50c/mL) was maintained in 94.3% on E/C/F/TAF vs 86.8% on ATV/r+F/TDF with virologic failure in 1.9%, 3.8%, respectively. More women on E/C/F/TAF achieved &lt;20c/mL at W48 compared with ATV/r+F/TDF (84.9% versus 71.7%p=0.041). No treatment emergent resistance was detected in either group. Mean% increase in BMD was higher in the TAF group for both lumbar spine and total hip. Multiple markers of renal safety were improved for participants randomised to TAF. No cases of proximal renal tubulopathy were reported. Nineteen women became pregnant during the switch study 13 E/C/F/TAF, 6 ATV/r+F/TDF,3 normal infants have been delivered in each group to date.DiscussionThese data demonstrate that women who switch to an integrase inhibitor+TAF-based regimen maintain high levels of virologic suppression with improvement in BMD and renal function biomarkers compared with those remaining on their ATV/r+TDF-based regimen.

P074 Significant efficacy and long term safety difference with taf-based str in naïve adults

IntroductionAt Week(W) 48, elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide (E/C/F/TAF) was statistically noninferior to E/C/F/tenofovir disoproxil fumarate(TDF) for the proportion of subjects with HIV-1 RNA &lt;50 copies (c)/mL and had significant improvements in renal and bone safety endpoints. We report W144 data.MethodsARV-naïve participants randomised 1:1 to receive E/C/F/TAF or E/C/F/TDF. W144 viral suppression (HIV-1-RNA &lt;50 and &lt;20 c/mL) by FDA snapshot analysis, pre-defined bone and renal safety, and tolerability endpoints are reported.Results1,733 HIV-infected adults were randomised and treated: 15% women, 43% non-white, 23% viral load (VL) &gt;100,000 c/mL. Median baseline characteristics: age 34 years, CD4 count 405 cells/µL, and VL 4.58 log10c/mL. At W144, E/C/F/TAF met pre-specified criteria for both non-inferiority and superiority to E/C/F/TDF by FDA snapshot algorithm (HIV-1-RNA &lt;50 and &lt;20 c/mL) (Table 1). Mean decrease in BMD was significantly less in the E/C/F/group for lumbar spine and hip (Table1). Multiple measures of renal safety were significantly better for participants on E/C/F/TAF (Table). No cases of renal tubulopathy in the E/C/F/TAF group vs 2 on E/C/F/TDF. No participants on E/C/F/TAF had renal-related discontinuations vs 12 on E/C/F/TDF (p&lt;0.001). Participants on E/C/F/TAF had greater increases in lipids.DiscussionE/C/F/TAF was significantly superior than E/C/F/TDF, driven by fewer participants on E/C/F/TAF with no W144 data. E/C/F/TAF continued to have a statistically superior bone and renal safety profile compared with E/C/F/TDF, demonstrating significant safety advantages over E/C/F/TDF through 3 years of treatment. Individuals on E/C/F/TAF had greater plasma lipid changes, but proportions starting lipid-lowering therapy were comparable.

SP022MOLECULAR CHARACTERIZATION OF A NOVEL MUTATION IN THE RENAL NACL COTRANSPORTER CAUSING GITELMAN'S SYNDROME BY IMPAIRING TRANSPORTER TRAFFICKING

Mutations affecting the sodium-chloride cotransporter (NCC) in the distal convoluted tubule of the nephron are causative of Gitelman'€™s syndrome (GS), a rare autosomal recessive disease characterized by electrolytic alterations similar to those induced by high dose thiazide treatment. Notably, the co-existence of hypomagnesemia and hypocalciuria is a feature of GS which is a distinguish hallmark from another hypokalemic renal tubulopathy, the Bartter'€™s syndrome (BS). Commonly GS is heterozygous compound with an estimated prevalence of 1:40000 and can be silent for years before the revealing in the early adulthood. Recognizing the genetic background is fundamental for the screening and the diagnosis of the disease, as recently studies showed that mutation affecting regulators of renal salt handling are underestimated in the general population. In a registry of BS/GS based at our University we discovered a novel point mutation (c.1204G>A which codify for an amino acid exchange G394D) in the sodium-chloride cotransporter NCC (SLC12A3) in a young woman with hypokalemia, hypomagnesemia and hypocalciuria associated to muscle pain and cramps. The present study aimed to investigate how this mutation affects NCC function by using a molecular biology approach and providing functional evidences. After a prior screening with bioinformatics tools predicting the possible pathogenicity of the mutation, were created different expression vectors with either the wild-type (wt-NCC) or the mutated G394D-NCC sequences. DNA and in-vitro transcribed RNA were afterwards transfected in a human embryonic kidney cells line (HEK293) and injected into oocytes deriving from Xenopus Laevis frog respectively. In transfected HEK 293 cells, wildtype NCC was detected by immunoblotting as two bands at approximately 130 kDa and 115 kDa corresponding to fully and core-glycosylated NCC, respectively. In contrast, G394D-NCC was seen as a single band at about 115 kDa only, suggesting an impaired maturation of the mutated protein. Similar findings were made in the oocyte expression system. Confocal microscopy on the oocytes, did also show a strong cell surface localization of wildtype NCC while mutated NCC was retained at intracellular compartments. Consistently, a decent thiazide-sensitive 22Na+ uptake into injected oocytes was only found for wildtype but not mutated NCC. Taken together all the findings in this study, a novel GS point mutation has been characterized to diminish NCC function by impairing trafficking of the protein to the cell surface. The absence of any mature glycosylation form of G394D-NCC suggests that the mutation impairs protein folding leading to a retention of NCC in the endoplasmic reticulum.

Tenofovir and adefovir down-regulate mitochondrial chaperone TRAP1 and succinate dehydrogenase subunit B to metabolically reprogram glucose metabolism and induce nephrotoxicity

Despite the therapeutic success of tenofovir (TFV) for treatment of HIV-1 infection, numerous cases of nephrotoxicity have been reported. Mitochondrial toxicity has been purported as the major target of TFV-associated renal tubulopathy but the underlying molecular mechanism remains unclear. In this report, we use metabolomics and proteomics with HK-2 cells and animal models to dissect the molecular pathways underlying nephropathy caused by TFV and its more toxic analog, adefovir (ADV). Proteomic analysis shows that mitochondrial chaperone TRAP1 and mtDNA replicating protein SSBP1 were significantly down-regulated in TFV and ADV treated HK-2 cells compared with controls. Transmission electron microscopy (TEM) revealed that TFV and ADV-treated HK-2 cells had accumulated glycogen, a phenotype that was also observed in mice treated with TFV and ADV. Analysis of the proteins in TCA cycle showed succinate dehydrogenase subunit B (SDHB) was nearly depleted in glucose oxidative phosphorylation pathway however certain enzymes in the glycolysis and glycogen synthesis pathway had elevated expression in TFV and ADV-treated HK-2 cells. These results suggest that TFV and ADV may cause mitochondrial dysfunction in renal tubular cells and reprogramming of glucose metabolism. The resulting glycogen accumulation may partially contribute to TFV and ADV induced renal dysfunction.

Hyperinsulinaemic hypoglycaemia, renal Fanconi syndrome and liver disease due to a mutation in the HNF4A gene.

SummaryHNF4A gene mutations have been reported in cases of transient and persistent hyperinsulinaemic hypoglycaemia of infancy (HHI), particularly in families with adulthood diabetes. The case of a patient with HHI, liver impairment and renal tubulopathy due to a mutation in HNF4A is reported.Learning points:Urine specimen study in cases of HHI with diazoxide response is necessary to rule out specific metabolic conditions (l-3-hydroxyacyl-coenzyme A dehydrogenase deficiency) or tubular renal involvement.Hyperinsulinaemic hypoglycaemia due to the heterozygous mutation (p.Arg63Trp, c. 187C > T) in the HNF4A gene is associated with renal tubulopathy and liver involvement.Follow-up of patients diagnosed of HHI is mandatory to detect associated conditions.

TRNA N6-adenosine threonylcarbamoyltransferase defect due to KAE1/TCS3 (OSGEP) mutation manifest by neurodegeneration and renal tubulopathy

Post-transcriptional tRNA modifications are numerous and require a large set of highly conserved enzymes in humans and other organisms. In yeast, the loss of many modifications is tolerated under unstressed conditions; one exception is the N6-threonyl-carbamoyl-adenosine (t6A) modification, loss of which causes a severe growth phenotype. Here we aimed at a molecular diagnosis in a brother and sister from a consanguineous family who presented with global developmental delay, failure to thrive and a renal defect manifesting in proteinuria and hypomagnesemia. Using exome sequencing, the patients were found to be homozygous for the c.974G>A (p.(Arg325Gln)) variant of the KAE1 gene. KAE1 is a constituent of the KEOPS complex, a five-subunit complex that catalyzes the second biosynthetic step of t6A in the cytosol. The yeast KAE1 allele carrying the equivalent mutation did not rescue the t6A deficiency of the kae1Δ yeast strain as efficiently as the WT allele; furthermore, t6A levels quantified by LC-MS/MS were lower in the kae1Δ strain which was complemented by the mutation than in the kae1Δ strain, which was complemented by the WT allele. We conclude that homozygosity for c.974G>A (p.(Arg325Gln)) in KAE1 likely exerts its pathogenic effect by perturbing t6A synthesis, thereby interfering with global protein production. This is the first report of t6A biosynthesis defect in human. KAE1 joins the growing list of cytoplasmic tRNA modification enzymes, all associated with severe neurological disorders.

Decline in eGFR identifies risk of TDF-induced renal tubulopathy

Decline in eGFR identifies risk of TDF-induced renal tubulopathy

The renal tubular damage marker urinary N-acetyl-\u03b2-d-glucosaminidase may be more closely associated with early detection of atherosclerosis than the glomerular damage marker albuminuria in patients with type 2 diabetes

BackgroundTo determine the association between urinary N-acetyl-β-d-glucosaminidase (NAG), a marker of renal tubulopathy, and carotid intima-media thickness (IMT) and plaques in patients with type 2 diabetes mellitus (T2D) and to compare the predictive value of NAG versus albuminuria, a marker of renal glomerulopathy.MethodsA total of 343 participants were enrolled in this retrospective cross-sectional study. We recruited participants with T2D who were tested for blood glucose parameters, urinary NAG, and urinary albumin-to-creatinine ratio (ACR) and had been checked for carotid ultrasonography.ResultsWe classified participants into a below-median urinary NAG group (Group I; n = 172) or an above-median group (Group II; n = 171). Mean, maximum, and mean of maximum carotid IMT and the proportion of patients with carotid plaques were significantly higher in Group II compared with Group I. In multiple linear regression analyses, high urinary NAG (Group II) was significantly associated with carotid IMT, independently of urinary ACR and other confounding factors. In terms of carotid plaques, both urinary NAG and ACR were significantly higher in participants with carotid plaques than in those without carotid plaques. After adjustment for confounding factors, both urinary NAG and ACR were significantly associated with the presence of carotid plaques.ConclusionsElevated urinary NAG, a marker of renal tubular damage, was related to increased carotid IMT and the presence of carotid plaques in patients with T2D. Urinary NAG may be a more sensitive biomarker than urinary albumin for early detection of atherosclerosis.

Treatment-limiting renal tubulopathy in patients treated with tenofovir disoproxil fumarate

Tenofovir disoproxil fumarate (TDF) is widely used in the treatment or prevention of HIV and hepatitis B infection. TDF may cause renal tubulopathy in a small proportion of recipients. We aimed to study the risk factors for developing severe renal tubulopathy. We conducted an observational cohort study with retrospective identification of cases of treatment-limiting tubulopathy during TDF exposure. We used multivariate Poisson regression analysis to identify risk factors for tubulopathy, and mixed effects models to analyse adjusted estimated glomerular filtration rate (eGFR) slopes. Between October 2002 and June 2013, 60 (0.4%) of 15,983 patients who had received TDF developed tubulopathy after a median exposure of 44.1 (IQR 20.4, 64.4) months. Tubulopathy cases were predominantly male (92%), of white ethnicity (93%), and exposed to antiretroviral regimens that contained boosted protease inhibitors (PI, 90%). In multivariate analysis, age, ethnicity, CD4 cell count and use of didanosine or PI were significantly associated with tubulopathy. Tubulopathy cases experienced significantly greater eGFR decline while receiving TDF than the comparator group (-6.60 [-7.70, -5.50] vs. -0.34 [-0.43, -0.26] mL/min/1.73m2/year, p<0.0001). Older age, white ethnicity, immunodeficiency and co-administration of ddI and PI were risk factors for tubulopathy in patients who received TDF-containing antiretroviral therapy. The presence of rapid eGFR decline identified TDF recipients at increased risk of tubulopathy.

Liver Cancer in Tyrosinemia Type 1.

Hereditary Tyrosinemia type I (HT1) is clinically mainly characterised by severe liver disease. Most patients present in their first months of life with liver failure, but others can present later with issues of compensated cirrhosis, renal tubulopathy or acute intermittent porphyria. If patients survive the acute phase with liver failure or if they present later with compensated cirrhosis, they often develop hepatocellular carcinoma early but also later in life. The course of the disease changed after the introduction of 2-(2 nitro-4-3 trifluoro-methylbenzoyl)-1, 3-cyclohexanedione (NTBC), which blocks the tyrosine degradation pathway at an earlier step. Therefore, the toxic products did not accumulate anymore and all clinical problems resolved. However, the risk (although clearly decreased) for developing liver cancer remained, especially if NTBC treatment is initiated late, a slow decrease of the tumor marker α-fetoprotein is seen or if the α-fetoprotein concentrations remain just above the normal range. A rise of α-fetoprotein in these HT1 patients is more or less pathognomonic for liver cancer. Although hepatoblastoma development occurs in HT1 patients, most HT1 patients develop hepatocellular carcinoma (HCC) or a mixed type of carcinoma consisting of HCC and hepatoblastoma. Due to the small risk of liver cancer development, screening for liver cancer (especially HCC) is still recommended in HT1 patients using regular measures of α-fetoprotein and imaging. Ultrasound is mostly the modality of choice for surveillance, because it is widely available, it does not use radiation and is noninvasive. When a suspicious lesion is present, the higher sensitivity of MRI could be used for characterization and staging of lesions. At this moment, no HCC development in pre-symptomatically treated patients is reported. These different situations could possibly indicate that NTBC can prevent the start of the development of HCC when initiated early, but can't stop the development of HCC if it is prescribed at a later stage, stressing the importance of early diagnosis.

Etiology of Renal Tubulopathy in Iranian Children-A Nationwide Survey

Introduction: Inherited and acquired renal tubular disorders including cystic Kidney disease, cystinosis, Bartter’s syndrome, Liddle syndrome, Gordon syndrome, nephrogenic diabetes insipidus, and drug-induced tubular injury are the frequent causes of end stage renal disease (ESRD) in children manifesting with chronic kidney disease (CKD). This is a report of the etiology and incidence of tubulopathies in a cohort of Iranian children across the country. Materials and Methods : This descriptive observational study was conducted from March 2013 to October 2013. A list of tubulopathy disorders was emailed to 70 members of the Iranian Society of Pediatric Nephrology in different provinces of Iran practicing in both university affiliated and non-affiliated hospitals. They were requested to report the number of patients with specific International Classification of Disease (ICD-10) codes admitted to their hospitals between 2006 and 2013. Data are presented as numbers and percentages. Results: Of 31 participating centers, 23 completed and returned the spreadsheets. Of the 2940 reported cases,the three most frequent tubulopathies were renal tubular acidosis (RTA) (33%), calcium disorders (27%), and cystic diseases (17%). Considering Tehran and Shiraz as referral centers, RTA and cystinosis were mostly reported from Kermanand Urmia, respectively. Furthermore, idiopathic hypercalciuria, cystinuria, and hyperoxaluria were the most common causes of hereditary kidney stone in 281 children reported from Bandarabas, Tabriz, and Shiraz, respectively Conclusions : Our findings regarding the high incidence and different etiologies of inherited tubulopathies may provide a basis for designing targeted therapeutic interventions in the future and strategies for gene therapy of these complex disorders. Keywords : Kidney Tubules; Disease; Acidosis; Renal Tubule; Kidney disease; Cyst; Diabetes Insipidus; Urolithiasis; Bartter syndrome.