CLC anion transporters are found in all phyla and form a gene family of eight members in mammals. Two CLC proteins, each of which completely contains an ion translocation parthway, assemble to homo...

https://www.physiology.org/doi/pdf/10.1152/physrev.00047.2017

CLC Chloride Channels and Transporters: Structure, Function, Physiology, and Disease.

https://www.amjmed.com/article/S0002-9343(01)01086-5/pdf

Clinical presentation of genetically defined patients with hypokalemic salt-losing tubulopathies.

Mutations in genes encoding chloride transporters cause Bartter's syndrome. An antenatal form associated with salt wasting and deafness has been observed in persons with mutations in BSND, the gene...

https://www.nejm.org/doi/pdf/10.1056/NEJMoa032843

Salt wasting and deafness resulting from mutations in two chloride channels.

It is now evident that the term Bartter syndrome does not represent a unique entity but encompasses a variety of disorders of renal electrolyte transport. Application of molecular biology techniques has permitted a better understanding of these “Bartter-like syndromes,” which at present can be divided into three different genetic and clinical entities. Neonatal Bartter syndrome is observed in newborn infants and characterized by polyhydramnios, premature delivery, life-threatening episodes of fever and dehydration during the early weeks of life, growth retardation, hypercalciuria, and early-onset nephrocalcinosis. Two molecular defects have been identified: either at the gene encoding the renal bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2) or the gene encoding an ATP-sensitive inwardly rectifying K channel (ROMK). “Classic” Bartter syndrome is mostly observed during infancy and childhood and is characterized clinically by polyuria and growth retardation. Nephrocalcinosis is not present. Very recently, either deletions or mutations at the gene encoding a renal chloride channel (ClC-Kb) have been identified. Gitelman syndrome is observed in older children and adults presenting with intermittent episodes of muscle weakness and tetany, hypokalemia, and hypomagnesemia. Mutations at the gene encoding the thiazide-sensitive Na-Cl cotransporter have been identified in the majority of patients studied. Obviously the validity of this classification must be confirmed in the near future when all mutations have been described and genotypic-phenotypic correlations are better defined.

Bartter and related syndromes : the puzzle is almost solved

The genetic basis and cellular defects of a number of primary magnesium wasting diseases have been elucidated over the past decade. This review correlates the clinical pathophysiology with the primary defect and secondary changes in cellular electrolyte transport. The described disorders include (1) hypomagnesemia with secondary hypocalcemia, an earlyonset, autosomal-recessive disease segregating with chromosome 9q12-22.2; (2) autosomal-dominant hypomagnesemia caused by isolated renal magnesium wasting, mapped to chromosome 11q23; (3) hypomagnesemia with hypercalciuria and nephrocalcinosis, a recessive condition caused by a mutation of the claudin 16 gene (3q27) coding for a tight junctional protein that regulates paracellular Mg(2+) transport in the loop of Henle; (4) autosomal-dominant hypoparathyroidism, a variably hypomagnesemic disorder caused by inactivating mutations of the extracellular Ca(2+)/Mg(2+)-sensing receptor, CASR: gene, at 3q13.3-21 (a significant association between common polymorphisms of the CASR: and extracellular Mg(2+) concentration has been demonstrated in a healthy adult population); and (5) Gitelman syndrome, a recessive form of hypomagnesemia caused by mutations in the distal tubular NaCl cotransporter gene, SLC12A3, at 16q13. The basis for renal magnesium wasting in this disease is not known. These inherited conditions affect different nephron segments and different cell types and lead to variable but increasingly distinguishable phenotypic presentations. No doubt, there are in the general population other disorders that have not yet been identified or characterized. The continued use of molecular techniques to probe the constitutive and congenital disturbances of magnesium metabolism will increase the understanding of cellular magnesium transport and provide new insights into the way these diseases are diagnosed and managed.

/pdf/inherited-disorders-of-renal-magnesium-handling-2dcpvlbgc6.pdf

Inherited Disorders of Renal Magnesium Handling

The infantile variant of Bartter syndrome (IBS) is usually associated with maternal polyhydramnios, premature birth, postnatal polyuria and hypokalemic hypochloremic metabolic alkalosis and a typical appearance. IBS is thought to be an autosomal recessive trait. Several congenital tubular defects are associated with sensorineural deafness (SND). However, an association between the IBS and SND has not been reported so far. Here we describe 5 children of an extended consanguineous Bedouin family with IBS and SND. In 3 of the cases, the typical electrolyte imbalance and facial appearance were detected neonatally. SND was detected as early as age 1 month, suggesting either coincidental homozygotization of 2 recessive genes or a pleiotropic effect of one autosomal recessive gene. This association suggests that evaluation of SND is warranted in every case of IBS.

Meli Ohaly

Papers

Infantile variant of Bartter syndrome and sensorineural deafness: a new autosomal recessive disorder.