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BACKGROUND: Hyperkalemia is a frequent electrolyte alteration whose prevalence varies widely, depending on the adopted cutoff, the setting (inpatients versus outpatients), and the characteristics of the study population. Familial hyperkalemic hypertension (FHH) is a rare cause of hypertension, hyperkalemia, and hyperchloremic metabolic acidosis. METHODS: In this retrospective observational study, we investigated the prevalence of hyperkalemia (serum K+ >5.2 mmol/L on 2 repeated measurements) in 5100 referred patients affected by arterial hypertension, the potential causes, and the associated cardiovascular risk profile. RESULTS: Overall, 374 (7.3%) patients had hyperkalemia. This was associated with drugs known to increase K+ levels (74.6%), chronic kidney disease (33.7%), or both (24.3%). Among the 60 patients with unexplained hyperkalemia, 3 displayed a clinical and biochemical phenotype suggestive of FHH that was genetically confirmed in 2 of them (0.04% in the entire cohort). FHH prevalence rose to 3.3% in patients with unexplained hyperkalemia and up to 29% (2/7) if they had serum K+ >5.8 mmol/L. The genetic cause of FHH was a missense variant affecting the acidic motif of WNK1 in 1 family and a rare CUL3 splicing variant, whose functional significance was confirmed by a minigene assay, in another. Finally, we observed a significant association between hyperkalemia and the occurrence of cardiovascular events, metabolic syndrome, and organ damage, independent of potential confounding factors. CONCLUSIONS: The identification of hyperkalemia in patients with hypertension has prognostic implications. A timely diagnosis of FHH is important for effective management of hypertension, electrolyte imbalance correction with tailored treatment, and genetic counseling. [ABSTRACT FROM AUTHOR]

Gain-of-function mutations in with no lysine (K)1 (WNK1) and WNK4genes are responsible for familial hyperkalemic hypertension (FHHt), a rare, inherited disorder characterized by arterial hypertension and hyperkalemia with metabolic acidosis. More recently, FHHt-causing mutations in the Kelch-like 3-Cullin 3 (KLHL3-CUL3) E3 ubiquitin ligase complex have shed light on the importance of WNK's cellular degradation on renal ion transport. Using full exome sequencing for a 4-generation family and then targeted sequencing in other suspected cases, we have identified new missense variants in the WNK1 gene clustering in the short conserved acidic motif known to interact with the KLHL3-CUL3 ubiquitin complex. Affected subjects had an early onset of a hyperkalemic hyperchloremic phenotype, but normal blood pressure values' Functional experiments in Xenopus laevis oocytes and HEK293T cells demonstrated that these mutations strongly decrease the ubiquitination of the kidney-specific isoform KS-WNK1 by the KLHL3-CUL3 complex rather than the long ubiquitous catalytically active L-WNK1 isoform. A corresponding CRISPR/Cas9 engineered mouse model recapitulated both the clinical and biological phenotypes. Renal investigations showed increased activation of the Ste20 proline alanine-rich kinase-[Na.sup.+]-[Cl.sup.-] cotransporter (SPAK-NCC) phosphorylation cascade, associated with impaired ROMK apical expression in the distal part of the renal tubule. Together, these new WNK1 genetic variants highlight the importance of the KS-WNK1 isoform abundance on potassium homeostasis., Introduction Familial hyperkalemic hypertension (FHHt), also known as Gordon syndrome and pseudohypoaldosteronism type 2, is a rare disease associated with net positive [Na.sup.+] balance and renal [K.sup.+] retention resulting in [...]

Background Prenatal diagnosis of hyperechogenic kidneys is associated with a wide range of etiologies and prognoses. The recent advances in fetal ultrasound associated with the development of next-generation sequencing for molecular analysis have enlarged the spectrum of etiologies, making antenatal diagnosis a very challenging discipline. Of the various known causes of hyperechogenic fetal kidneys, calcium and phosphate metabolism disorders represent a rare cause. An accurate diagnosis is crucial for providing appropriate genetic counseling and medical follow-up after birth. Methods We report on three cases of fetal hyperechogenic kidneys corresponding to postnatal diagnosis of nephrocalcinosis. In all cases, antenatal ultrasound showed hyperechogenic kidneys of normal to large size from 22 gestational weeks, with a normal amount of amniotic fluid. Postnatal ultrasound follow-up showed nephrocalcinosis associated with hypercalcemia, hypercalciuria, elevated 1,25(OH).sub.2-vitamin D, and suppressed parathyroid hormone levels. Results Molecular genetic analysis by next-generation sequencing performed after birth in the three newborns revealed biallelic pathogenic variants in the SLC34A1 gene, encoding the sodium/phosphate cotransporter type 2 (Npt2a), confirming the diagnosis of infantile hypercalcemia. Conclusions Nephrocalcinosis due to infantile hypercalcemia can be a cause of fetal hyperechogenic kidneys, which suggests early antenatal anomaly of calcium and phosphate metabolism. This entity should be considered in differential diagnosis. Postnatal follow-up of infants with hyperechogenic kidneys should include evaluation of calcium and phosphate metabolism., Author(s): Marguerite Hureaux [sup.1] [sup.2] [sup.3] , Arnaud Molin [sup.4] [sup.5] [sup.6] , Nadine Jay [sup.7] , Anne Hélène Saliou [sup.8] , Emmanuel Spaggiari [sup.9] , Rémi Salomon [sup.2] [sup.3] [...]

Background Hypomagnesaemia with secondary hypocal-caemia (HSH) is a rare autosomal recessive disorder caused by pathogenic variants in TRPM6 , encoding the channel-kinase transient receptor potential melastatin type 6. Patients have very low serum magnesium (Mg2+) levels and suffer from muscle cramps and seizures. Despite genetic testing, a subgroup of HSH patients remains without a diagnosis. Methods In this study, two families with an HSH phenotype but negative for TRPM6 pathogenic variants were subjected to whole exome sequencing. Using a complementary combination of biochemical and functional analyses in overexpression systems and patient-derived fibroblasts, the effect of the TRPM7 -identified variants on Mg2+ transport was examined. Results For the first time, variants in TRPM7 were identified in two families as a potential cause for hereditary HSH. Patients suffer from seizures and muscle cramps due to magnesium deficiency and episodes of hypocalcaemia. In the first family, a splice site variant caused the incorporation of intron 1 sequences into the TRPM7 messenger RNA and generated a premature stop codon. As a consequence, patient-derived fibroblasts exhibit decreased cell growth. In the second family, a heterozygous missense variant in the pore domain resulted in decreased TRPM7 channel activity. Conclusions We establish TRPM7 as a prime candidate gene for autosomal dominant hypomagnesaemia and secondary hypocalcaemia. Screening of unresolved patients with hypocalcaemia and secondary hypocalcaemia may further establish TRPM7 pathogenic variants as a novel Mendelian disorder. [ABSTRACT FROM AUTHOR]

Objective: Familial hypocalciuric hypercalcaemia type 1 (FHH1), related to heterozygous loss‐of‐function mutations of the calcium‐sensing receptor gene, is the main differential diagnosis for primary hyperparathyroidism. The aim of our study was to describe clinical characteristics of adult patients living in France with a genetically confirmed FHH1. Design and patients: This observational, retrospective, multicentre study included 77 adults, followed up in 32 clinical departments in France, with a genetic FHH1 diagnosis between 2001 and 2012. Results: Hypercalcaemia was diagnosed at a median age of 53 years [IQR: 38‐61]. The diagnosis was made after clinical manifestations, routine analysis or familial screening in 56, 34 and 10% of cases, respectively, (n = 58; data not available for 19 patients). Chondrocalcinosis was present in 11/51 patients (22%), bone fractures in 8/56 (14%) and renal colic in 6/55 (11%). The median serum calcium was 2.74 mmol/L [IQR: 2.63‐2.86 mmol/L], the median plasma parathyroid hormone level was 4.9 pmol/L [3.1‐7.1], and the median 24‐hour urinary calcium excretion was 2.8 mmol/24 hours [IQR: 1.9‐4.0]. Osteoporosis (dual X‐ray absorptiometry) or kidney stones (renal ultrasonography) were found in 6/38 patients (16%) and 9/32 patients (28%), respectively. Fourteen patients (18%) underwent parathyroid surgery; parathyroid adenoma was found in three patients (21%) and parathyroid hyperplasia in nine patients (64%). No correlation between genotype and phenotype was established. Conclusion: This large cohort study demonstrates that FHH1 clinical characteristics can be atypical in 33 patients (43%). Clinicians should be aware of this rare differential diagnosis in order to adopt an appropriate treatment strategy. [ABSTRACT FROM AUTHOR]

The rise of genetics in the last decades has allowed major advances in the understanding of the mechanisms leading to inherited kidney diseases. From the first positional cloning studies to the advent of high-throughput sequencing (NGS), genome analysis technologies have become increasingly efficient, with an extraordinary level of resolution. Moreover, sequencing prices have decreased from one million dollars for the sequencing of James Watson's genome in 2008, to a few hundred dollars for the sequencing of a genome today. Thus, molecular diagnosis has a central place in the diagnosis of these patients and influences the therapeutic management in many situations. However, although NGS is a powerful tool for the identification of variants involved in diseases, it also exposes to the risk of over-interpretation of certain variants, leading to erroneous diagnoses, requiring the use of specialists. In this review, we first propose a brief retrospective of the essential steps that led to the current knowledge and the development of NGS for the study of hereditary nephropathies in children. This review is then an opportunity to present the main hereditary nephropathies and the underlying molecular mechanisms. Among them, we emphasize ciliopathies, congenital anomalies of the kidney and urinary tract, podocytopathies and tubulopathies., (© 2023 médecine/sciences – Inserm.)