Pre-pubertal growth in the hyperprostaglandin E syndrome

Diagnosis and management of Bartter syndrome: executive summary of the consensus and recommendations from the European Rare Kidney Disease Reference Network Working Group for Tubular Disorders

Bartter syndrome is a rare inherited salt-losing renal tubular disorder characterized by secondary hyperaldosteronism with hypokalemic and hypochloremic metabolic alkalosis and low to normal blood pressure. The primary pathogenic mechanism is defective salt reabsorption predominantly in the thick ascending limb of the loop of Henle. There is significant variability in the clinical expression of the disease, which is genetically heterogenous with 5 different genes described to date. Despite considerable phenotypic overlap, correlations of specific clinical characteristics with the underlying molecular defects have been demonstrated, generating gene-specific phenotypes. As with many other rare disease conditions, there is a paucity of clinical studies that could guide diagnosis and therapeutic interventions. In this expert consensus document, the authors have summarized the currently available knowledge and propose clinical indicators to assess and improve quality of care.

Bartter- and Gitelman-like syndromes: salt-losing tubulopathies with loop or DCT defects

Salt-losing tubulopathies with secondary hyperaldosteronism (SLT) comprise a set of well-defined inherited tubular disorders. Two segments along the distal nephron are primarily involved in the pathogenesis of SLTs: the thick ascending limb of Henle's loop, and the distal convoluted tubule (DCT). The functions of these pre- and postmacula densa segments are quite distinct, and this has a major impact on the clinical presentation of loop and DCT disorders - the Bartter- and Gitelman-like syndromes. Defects in the water-impermeable thick ascending limb, with its greater salt reabsorption capacity, lead to major salt and water losses similar to the effect of loop diuretics. In contrast, defects in the DCT, with its minor capacity of salt reabsorption and its crucial role in fine-tuning of urinary calcium and magnesium excretion, provoke more chronic solute imbalances similar to the effects of chronic treatment with thiazides. The most severe disorder is a combination of a loop and DCT disorder similar to the enhanced diuretic effect of a co-medication of loop diuretics with thiazides. Besides salt and water supplementation, prostaglandin E2-synthase inhibition is the most effective therapeutic option in polyuric loop disorders (e.g., pure furosemide and mixed furosemide-amiloride type), especially in preterm infants with severe volume depletion. In DCT disorders (e.g., pure thiazide and mixed thiazide-furosemide type), renin-angiotensin-aldosterone system (RAAS) blockers might be indicated after salt, potassium, and magnesium supplementation are deemed insufficient. It appears that in most patients with SLT, a combination of solute supplementation with some drug treatment (e.g., indomethacin) is needed for a lifetime.

Longitudinal growth in chronic hypokalemic disorders

Growth retardation remains a major complication in children with primary tubular disorders, despite adequate supplemental treatment with electrolytes, water and bicarbonate. Chronic hypokalemia, characteristic of some tubulopathies, impairs growth by mechanisms that are not well known. Association with growth hormone deficiency has been reported in patients with Bartter's or Gitelman's syndrome. Tissue-specific alterations of growth hormone and insulin-like growth factor I axis have been described in experimental models of potassium depletion. Hypokalemic rats gain less body length and weight than pair-fed normokalemic animals and, by contrast, develop renal hypertrophy. These rats have low circulating concentrations of insulin-like growth factor I, depressed messenger ribonucleic acid (mRNA) levels of this peptide in the tibial growth plate, and they are resistant to the longitudinal growth-promoting effects of exogenous growth hormone. The reason for this resistance remains to be defined. No alterations in the intracellular signaling for growth hormone have been found in the liver of hypokalemic rats. However, treatment with high doses of growth hormone is unable to normalize hypertrophy of the epiphyseal cartilage chondrocytes, which are severely disturbed in potassium depletion and likely play an important role in the pathogenia of growth impairment in this condition.

Chronic renal failure in a boy with classic Bartter's syndrome due to a novel mutation in CLCNKB coding for the chloride channel

BACKGROUND

Progressive renal failure in patients with classic Bartter's syndrome (cBS) due to inactivating mutations in CLCNKB gene is extraordinarily rare.

DISCUSSION

We describe a 17-year-old Chinese boy who presented with progressive muscle weakness and renal failure. He was diagnosed as BS of unknown type at the age of 9 months and treated with indomethacin (2 mg/kg/day) and potassium chloride (KCl) supplementation (1.5 mEq/kg/day) for hypokalemia (2.5 mmol/l). At the age of 12 years, serum K+ was 3.0 mmol/l and creatinine reached 2.0 mg/dl. On admission, his blood pressure was normal but volume status was depleted. Urinalysis was essentially normal. Biochemical studies showed hypokalemia (K+ 2.4 mmol/l) with a high transtubular K+ gradient (TTKG) 9.6, metabolic alkalosis (HCO3- 28.4 mmol/l), normomagnesemia (2.0 mg/dl), severe renal failure (BUN 94 mg/dl, Cr 6.3 mg/dl), and hypocalciuria (urine calcium/creatinine ratio 0.02 mg/mg). Abdominal sonography revealed bilateral small size kidneys without nephrocalcinosis or renal stones. After the withdrawal of indomethacin with regular KCl and adequate fluid supplementation for 1 year, serum creatinine and K+ levels have been maintained at 4.0 mg/dl and 3.3 mmol/l, respectively. Direct sequencing of NKCC2, ROMK, ClC-Kb, and NCCT in this patient disclosed a novel homozygous missense mutation (GGG to GAG, G470E) in CLCNKB. This G470E mutation was not identified in 100 healthy Chinese subjects. Long-term therapy of non-steroidal anti-inflammatory drugs (NSAIDs), prolonged hypokalemia, chronic volume depletion, and underlying genetic variety may contribute to the deterioration of his renal function. The cautious use of NSAIDs, aggressive correction of hypokalemia, and avoidance of severe volume depletion may prevent the irreversible renal damage in patients with BS due to a Cl- channel defect.

The role of cyclooxygenases and prostanoid receptorsin furosemide-like salt losing tubulopathy: the hyperprostaglandin E syndrome

Hyperprostaglandin E syndrome/antenatal Bartter syndrome is characterized by NaCl wasting and volume depletion, juxtaglomerula hypertrophy, hyperreninism and secondary hyperaldosteronism. Primary causes are mutations in the gene for Na-K-2Cl-cotransporter, NKCC2, or for potassium channel, ROMK, responsible for medullary NaCl malabsorption. Most intriguing aspect of the syndrome is the association with a massively increased renal prostaglandin production which contributes substantially to the clinical picture of the patients. Therefore the term hyperprostaglandin E syndrome has been introduced. It is unclear how prostaglandins aggravate the NaCl transport deficiency. Aspects to prostaglandin synthesis and receptor-mediated function within the kidney in patients suffering from hyperprostaglandin E syndrome/antenatal Bartter syndrome will be discussed.

Pharmacotyping of hypokalaemic salt-losing tubular disorders

Long standing confusion exists in the terminology of hypokalaemic salt-losing tubulopathies (SLTs). SLTs are autosomal recessively transmitted and characterized by normotensive secondary hyperreninism/hyperaldosteronism with hypokalaemic metabolic alkalosis. Historically, four phenotypical variants have been described: (1) the (classic) Bartter syndrome (cBS), (2) the hypomagnesaemic hypocalciuric Gitelman syndrome (GS), (3) the hypercalciuric hyperprostaglandin-E-syndrome (HPS) or antenatal Bartter syndrome (aBS) and (4) the hyperprostaglandin-E-syndrome with sensorineural deafness (HPS + SND). The latter two syndromes are the most severe variants with antenatal manifestation with polyhydramnios and life-threatening course of salt- and water-loss. Defects in five renal membrane proteins involved in electrolyte reabsorption have been identified: In HPS-patients mutations in (1) either the furosemide-sensitive sodium-potassium-chloride cotransporter NKCC2, or (2) in the potassium channel ROMK have been identified, and (3) HPS + SND is caused by mutations in the beta-subunit of the chloride channels ClC-Kb and -Ka (named barttin), all mimicking the major pharmacological effects of furosemide with minor potassium-wasting in ROMK-patients as seen in patients treated with simultaneous furosemide and amiloride, and minor calcium-wasting in Barttin-patients resembling the combination of furosemide and thiazides. (4) cBS is caused by mutations in the chloride channel ClC-Kb with similar clinical characteristics as seen under combination of thiazides and furosemide, (5) GS is caused by mutations in the thiazide-sensitive sodium-chloride cotransporter NCCT resembling the effect of long-term thiazide administration.

CONCLUSION

The combination of pharmacology and genetics suggests a new terminology for the above described SLTs: Furosemide-like-SLT for HPS caused by NKCC2-mutations, furosemide/amiloride-like-SLT for HPS caused by ROMK-mutations, furosemide/thiazide-like-SLT for HPS + SND, thiazide/furosemide-like-SLT for cBS, and thiazide-like-SLT for GS.

The neonatal variant of Bartter syndrome and deafness: preservation of renal function

BACKGROUND

A subtype of antenatal Bartter syndrome and sensorineural deafness (BSND) was originally described among families from southern Israel, and its gene (Barttin, OMIM #606412) has recently been identified. A report has suggested that these children develop chronic renal insufficiency during childhood attributable to chronic tubulointerstitial fibrosis and atrophy.

METHODS

Data from 13 infants with BSND, who were born during a 20-year period in our institution, were retrospectively analyzed.

RESULTS

All pregnancies were complicated by polyhydramnion and premature birth. All patients have sensorineural deafness, as well as hypokalemic metabolic alkalosis. Persistent hypercalciuria or nephrocalcinosis were absent in most children. All children have been treated with indomethacin (2 mg/kg/d) and potassium supplementation. The current average serum creatinine and calculated creatinine clearance from the older group (n = 8; mean age: 8.8 +/- 1.4 years) is 60.8 +/- 16.5 micro mol/L and 95 +/- 20 mL/min/1.73m(2), respectively. Kidney biopsies from two 7-year-old patients revealed mild focal tubulointerstitial fibrosis and minimal mesangial proliferation but no glomerulosclerosis.

CONCLUSIONS

Early renal function deterioration is not a uniform finding among children with BSND mutations.

Inherited primary renal tubular hypokalemic alkalosis: a review of Gitelman and Bartter syndromes

Inherited hypokalemic metabolic alkalosis, or Bartter syndrome, comprises several closely related disorders of renal tubular electrolyte transport. Recent advances in the field of molecular genetics have demonstrated that there are four genetically distinct abnormalities, which result from mutations in renal electrolyte transporters and channels. Neonatal Bartter syndrome affects neonates and is characterized by polyhydramnios, premature delivery, severe electrolyte derangements, growth retardation, and hypercalciuria leading to nephrocalcinosis. It may be caused by a mutation in the gene encoding the Na-K-2Cl cotransporter (NKCC2) or the outwardly rectifying potassium channel (ROMK), a regulator of NKCC2. Classic Bartter syndrome is due to a mutation in the gene encoding the chloride channel (CLCNKB), also a regulator of NKCC2, and typically presents in infancy or early childhood with failure to thrive. Nephrocalcinosis is typically absent despite hypercalciuria. The hypocalciuric, hypomagnesemic variant of Bartter syndrome (Gitelman syndrome), presents in early adulthood with predominantly musculoskeletal symptoms and is due to mutations in the gene encoding the Na-Cl cotransporter (NCCT). Even though our understanding of these disorders has been greatly advanced by these discoveries, the pathophysiology remains to be completely defined. Genotype-phenotype correlations among the four disorders are quite variable and continue to be studied. A comprehensive review of Bartter and Gitelman syndromes will be provided here.

Diagnosis and clinical biochemistry of inherited tubulopathies

Epithelial ion channels and transporter proteins have physiologically important roles throughout the length of the nephron. Discovering the molecular identities of tubular epithelial cell proteins and their functional roles has increased understanding of both renal physiology and tubular diseases. Defects in tubular handling of solutes may present with nephrocalcinosis or nephrolithiasis, rickets, acid base, electrolyte or blood pressure disturbances. Biochemical analysis of both serum and urine, together with clinical history and examination, remain fundamental for their diagnosis, whilst understanding of underlying molecular mechanisms allows appropriate management.

Evaluation of long-term treatment with indomethacin in hereditary hypokalemic salt-losing tubulopathies

OBJECTIVE

Evaluation of the benefit/risk ratio of long-term treatment with indomethacin in salt-losing tubulopathies with special attention to renal function.

STUDY DESIGN

Twelve patients (median age, 14.9 years) had received indomethacin for a median of 13 years (median cumulative dose, 10.7 g/kg). Creatinine clearance, serum electrolyte levels, endocrine status, and excretion of prostaglandins and electrolytes were examined during indomethacin therapy and after its withdrawal. All patients underwent ultrasound-guided renal biopsy. For statistical evaluation, the Wilcoxon test and Pearson correlation coefficient were used.

RESULTS

After indomethacin withdrawal, the biochemical features of the tubulopathy reappeared. The median creatinine clearance rose from 67.4 to 96.5 mL/min/1.73 m(2) (P <.05) but remained subnormal in 4 patients. Ultrasonography elucidated medullary nephrocalcinosis in 8 patients. Renal tissue showed slight/moderate focal tubular atrophy and interstitial fibrosis in 8 patients. Comparison with biopsy specimens, obtained 11 to 14 years before study participation from 5 patients, revealed no progression. A correlation between fractional sodium and magnesium excretion and percentage of altered tubulointerstitial compartment was found (P <.001). The 4 patients with mutations in the gene of the inwardly rectifying adenosine triphosphate-regulated potassium channel (ROMK) had almost normal renal histologic findings and normal renal function.

CONCLUSION

Renal function and histology are unaffected by long-term indomethacin treatment.

Hypokalemic salt-losing tubulopathy with chronic renal failure and sensorineural deafness

OBJECTIVE

To characterize a rare inherited hypokalemic salt-losing tubulopathy with linkage to chromosome 1p31.

METHODS

We conducted a retrospective analysis of the clinical data for 7 patients in whom cosegregation of the disease with chromosome 1p31 had been demonstrated. In addition, in 1 kindred, prenatal diagnosis in the second child was established, allowing a prospective clinical evaluation.

RESULTS

Clinical presentation of the patients was homogeneous and included premature birth attributable to polyhydramnios, severe renal salt loss, normotensive hyperreninemia, hypokalemic alkalosis, and excessive hyperprostaglandin E-uria, which suggested the diagnosis of hyperprostaglandin E syndrome/antenatal Bartter syndrome. However, the response to indomethacin was only poor, accounting for a more severe variant of the disease. The patients invariably developed chronic renal failure. The majority had extreme growth retardation, and motor development was markedly delayed. In addition, all patients turned out to be deaf.

CONCLUSION

The hypokalemic salt-losing tubulopathy with chronic renal failure and sensorineural deafness represents not only genetically but also clinically a disease entity distinct from hyperprostaglandin E syndrome/antenatal Bartter syndrome. A pleiotropic effect of a single gene defect is most likely causative for syndromic hearing loss.

Dose related growth response to indometacin in Gitelman syndrome

Growth failure is a recognised feature of Gitelman syndrome, although it is not as frequent as in Bartter syndrome. Indometacin is reported to improve growth in Bartter syndrome, but not in Gitelman syndrome, where magnesium supplements are recommended. This paper presents 3 sisters with Gitelman syndrome who could not tolerate magnesium supplements, and whose hypotension and polyuria were eliminated by taking 2 mg/kg/day indometacin, but who grew poorly. However, increasing the indometacin dose to 4 mg/kg/day improved their growth significantly, without changing their symptoms or biochemistry. Gastrointestinal haemorrhage necessitated the use of misoprostol.

Treatment of childhood hypophosphatasia with nonsteroidal antiinflammatory drugs

Hypophosphatasia (HP) is an inborn error of metabolism that is characterized by reduced bone mineralization. The aim of this investigation was to evaluate treatment of incapacitating lower limb pain in patients with childhood HP using nonsteroidal antiinflammatory drugs (NSAID). All patients (seven boys; age 32 months to 16 years) presented with delayed walking, the typical waddling gait, muscular weakness of the lower limbs, and a limited walking distance. Six patients had severe diffuse lower limb pain following physical activity and were therefore treated with NSAID. The benefit of this treatment was evaluated clinically and by measurement of renally (PGE2) and systemically (PGE-M) derived prostaglandins (PG) in urine before and during therapy. After treatment with NSAID all six patients showed marked clinical improvement with reduced pain, increased muscle strength, and a normalized walking distance. Levels of PGE-M, which had been elevated in four patients prior to therapy, returned to normal. The use of NSAID in childhood HP should be considered as a possible therapeutic approach because the quality of life in these patients is markedly impaired by pain of the limbs. Elevated PG might play a role in the bone metabolism of HP patients.

Recombinant human growth hormone and Gitelman's syndrome

Gitelman's syndrome is a primary renal tubular disorder with hypokalemic metabolic alkalosis, hypocalciuria, and magnesium deficiency. Short stature is one of clinical manifestations in children. The pathogenesis of short stature in Gitelman's syndrome is not known. To evaluate whether growth hormone (GH) is deficient and whether recombinant human GH (rhGH) improves growth rate, rhGH therapy was tried in a child with Gitelman's syndrome. Both height and body weight were less than the third percentile. Laboratory and radiologic findings suggested GH deficiency. During the first 6 months, rhGH therapy with potassium supplement markedly elevated growth rate from 3.8 cm/yr to 12.0 cm/yr. After cessation of rhGH, height increment markedly decreased to the pretreatment level of 3.6 cm/yr during the second 6 months. Additionally, hypomagnesemia was corrected after rhGH therapy. Accordingly, GH deficiency may contribute to short stature in children with Gitelman's syndrome, and rhGH therapy would be an excellent adjunctive treatment for short children with Gitelman's syndrome whose condition is resistant to conventional therapies in terms of growth.

Bartter syndrome: unraveling the pathophysiologic enigma

Familial hypokalemic, hypochloremic metabolic alkalosis, or Bartter syndrome, is not a single disorder but rather a set of closely related disorders. These Bartter-like syndromes share many of the same physiologic derangements, but differ with regard to the age of onset, the presenting symptoms, the magnitude of urinary potassium (K) and prostaglandin excretion, and the extent of urinary calcium excretion. At least three clinical phenotypes have been distinguished: (1) classic Bartter syndrome; (2) the hypocalciuric-hypomagnesemic Gitelman variant; and (3) the antenatal hypercalciuric variant (also termed hyperprostaglandin E syndrome). The fundamental pathogenesis of this complex set of disorders has long fascinated and stymied investigators. Physiologic investigations have suggested numerous pathogenic models. The cloning of genes encoding renal transport proteins has provided molecular tools to begin testing these hypotheses. To date, molecular genetic analyses have determined that mutations in the gene encoding the thiazide-sensitive sodium-chloride (Na-Cl) cotransporter underlie the pathogenesis of the Gitelman variant. In comparison, the antenatal variant is genetically heterogeneous with mutations in the genes encoding either the bumetanide-sensitive sodium-potassium-chloride (Na-K-2Cl) cotransporter or the luminal, ATP-regulated, K channel. With these data, investigators have begun to unravel the pathophysiologic enigma of the Bartter-like syndromes. Further studies will help refine pathogenic models for this set of disorders as well as provide new insights into the normal mechanisms of renal electrolyte transport.

Prostanoid biosynthesis by blood monocytes of children with hyperprostaglandin E syndrome

Hyperprostaglandin E syndrome (HPS), the prenatal variant of Bartter's syndrome, is characterized by a marked and selective stimulation of prostaglandin E (PGE2) synthesis. In the study group HPS patients showed increased urinary levels of PGE2, an index of renal, and of 11 alpha-hydroxy-9,15-dioxo-2,3,4,5,20-pentanor-19-carboxyprostano ic acid (PGE-M), an index of systemic PGE2 synthesis of 470% and of 570%, respectively. In addition, plasma concentration of PGE-M was also elevated 6.3-fold when compared with a control group. The urinary levels of other prostanoids were unaltered. During indomethacin treatment in both groups prostanoid excretion rates were suppressed to similar levels. To investigate the origin of stimulated prostanoid biosynthesis in HPS patients CD14+ monocytes were isolated from plasma samples, and the prostanoid synthesis was analyzed. The pattern and amounts of metabolites synthesized from endogenous arachidonic acid pools did not vary significantly between monocytes of the HPS and the control group. Thromboxane A2 (TXA2) was formed as the major prostanoid product. Using PGH2 as an exogenous substrate, again no difference in PGE2 biosynthesis was observed, indicating no difference in PGE-synthetic activity between both groups. Additionally, mRNA expression analysis of CD14+ monocytes via RT-PCR delineated the constitutive expression of cyclooxygenase-1, cyclooxygenase-2, and thromboxane synthase mRNA in cells from HPS patients and controls without statistical differences between these two groups. In conclusion, our data show that monocytes are not the source for the increased PGE2 biosynthesis in children with HPS, and a genetic defect in PGE synthesis can be excluded as the primary event in the pathogenesis in HPS.