gitelman syndrome ( gs ) is an autosomal recessive salt - losing tubulopathy ( omim 263800 ) characterized by hypokalemic metabolic alkalosis , hypomagnesemia and hypocalciuria .
gs is caused by mutations in the slc12a3 gene encoding the na  cl co - transporter ( ncct ) of the distal convoluted tubule ( dct ) . to date , > 240 slc12a3 mutations have been identified in gs [ 3 , 4 ] .
as dct - mediated salt reabsorption accounts for only 5% of the filtered sodium load , gs has normally been described as having a mild salt - wasting phenotype that is often not detected until adolescence or early adulthood [ 3 , 5 , 6 ] .
bartter syndrome ( bs ) is a heterogeneous autosomal recessive salt - wasting condition that tends to present earlier in childhood with a more severe phenotype including significant salt wasting , polyuria and failure to thrive .
mutations affecting the na2clk co - transporter ( nkcc2 ; omim 601678 ) or the renal outer medullary potassium channel ( romk ; omim 241200 ) in the thick ascending limb ( tal ) often present antenatally with polyhydramnios , prematurity and severe salt wasting requiring significant electrolyte supplementation [ 8 , 9 ] .
hyperprostaglandin e syndrome following the description of elevated prostaglandin e2 ( pge2 ) levels in such cases .
it was this discovery that led to the successful treatment of these patients with the cyclo - oxygenase inhibitor indomethacin , which remains an important part of therapy along with salt and water supplementation .
type iii bs results from mutations that affect the basolateral chloride channel ( clc - kb ) in the dct and tal ( omim 607364 ) .
type iva bs with sensorineural deafness is the result of mutations in the barttin subunit of the clc - ka and clc - kb channels , which are expressed in the tal and inner ear ( omim 602522 ) .
digenic mutations of both the clc - ka and clc - kb channels have also been described causing bs with sensorineural deafness ( type ivb bs ; omim 613090 ) .
type v bs results from mutations leading to upregulation of the calcium sensing receptor ( casr ) and therefore hypocalcemia and hypercalciuria in addition to the typical salt - losing phenotype ( omim 601198 ) [ 15 , 16 ] .
most recently , the combination of epilepsy , ataxia , sensorineural deafness and salt wasting tubulopathy similar to gs has been associated with mutations of the inward - rectifying potassium channel kir 4.1 ( east syndrome ; omim 612780 ) .
we describe two female siblings presenting in infancy with hypokalemic metabolic alkalosis , severe failure to thrive , polyuria and increased pge2 excretion .
both siblings revealed a dramatic clinical response to indomethacin including improvements in growth and polyuria .
. however , genetic studies later confirmed a diagnosis of gs with the identification of compound heterozygous mutations in slc12a3 .
the first case is a caucasian female born at term weighing 3.2 kg ( appropriate for gestational age ) .
this was the mother 's first child with no history of spontaneous losses , consanguinity or family history of renal disease .
she first came to medical attention at the age of 5 months for failure to thrive with a weight of 4.8 kg and length of 59 cm ( height sds  1.2 , weight sds 2.1 ; figure  1 ) .
she was solely breast fed and thus supplementary formula feeds were introduced over the next month , but her weight fell further to 4.7 kg . at this time , she was reported to feed hourly with frequent vomiting , but no diarrhea .
a history of polyuria was noted by the parents with frequent changing of wet diapers .
gross motor delay was also noted as she had only just begun to roll and had significant head lag .
the treating pediatrician arranged for admission to the local hospital for further investigations and management . 

( a ) case 1 ( birth2 years ) ; arrow indicates start of indomethacin .
( c ) case 2 ( birth2 years ) ; arrow indicates start of indomethacin .
present ) ; arrow indicates increase in dose of indomethacin . growth profile of cases .
( a ) case 1 ( birth2 years ) ; arrow indicates start of indomethacin .
( c ) case 2 ( birth2 years ) ; arrow indicates start of indomethacin .
her chemistry profile demonstrated severe hyponatremia ( na 124 mmol / l ) and a hypokalemic ( k 2.1 mmol / l ) , hypochloremic ( cl 72 mmol / l ) metabolic alkalosis ( ph 7.59 , hco3 > 45
blood urea nitrogen ( bun ) and creatinine were within normal limits at 2.8 mmol / l and 29 mol / l , respectively .
mmol / l ( fractional excretion 0.63% ) and urine potassium 23.2 mmol / l ( fractional excretion 81% ) .
urine calcium : creatinine ( uca : cr ) ratio was elevated at 6 mmol : mmol with a normal serum calcium ( 2.53 mmol / l ) .
she was normotensive despite elevated plasma renin and aldosterone levels at 44 ng / l / s ( normal range 0.130.87 ng / l / s ) and 5795
renal ultrasound was normal with no evidence of dysplasia , cysts , stones or nephrocalcinosis .
she was initially treated with intravenous normal saline and added potassium chloride to stabilize the electrolyte abnormalities .
she was also commenced on oral supplementation of magnesium glucoheptonate ( 6 mg / kg / day of elemental mg ) and potassium chloride ( 5.5 mmol / kg / day ) .
with increasing doses of supplements , her hypokalemia , hypomagnesemia and metabolic alkalosis gradually improved over the next few months . however , at 1 year of age , her growth remained poor ( height sds 2.5 , weight sds 2.9 ; figure  1 ) .
consequently , the decision was made to start oral indomethacin ( 2 mg / kg / day divided bid ) . over the next 612 months
, she showed an excellent response to indomethacin with less polyuria , improved motor development and marked catch - up growth ( current height sds 0.37 , weight sds 1.05 ; figure  1 ) .
her uca : cr ratio , which was initially elevated , has been in the hypocalciuric range ( < 0.05 mmol : mmol ) since the age of 2 years .
her current regimen at 8 years of age includes indomethacin ( 3.5 mg / kg / day divided bid ) , potassium chloride ( 3.5 mmol / kg / day divided tid ) , amiloride ( 0.8 mg / kg once daily ) and magnesium glucoheptonate ( 13 mg of elemental mg / kg / day ) .
she consumes large quantities of high salt foods including feta cheese and olives on a daily basis .
her most recent bloodwork at 8 years of age shows stable electrolytes and blood gas values ( na 138 mmol / l , k 3.6 mmol / l , cl 99
mmol / l , mg 0.75 mmol / l , ph 7.40 , hco3 29 mmol / l ) .
mol / l [ estimated glomerular filtration rate ( egfr ) 84 ml / min/1.73 m ] . case 2 is the second child ( female ) born to the same parents at 36 weeks gestation weighing 2.5 kg ( appropriate for gestational age ) .
given her older sister s history ( case 1 ) , blood work was drawn at 1 week of age which demonstrated mild hyponatremia ( 132 mmol / l ) and metabolic alkalosis ( ph 7.64 , hco3 30 mmol / l ) .
the bun was mildly elevated at 5.3 mmol / l , consistent with volume depletion , and creatinine normal at 20
her first uca : cr ratio at 4 months of age was in the normal range ( 0.74 mmol : mmol ) with a normal serum calcium ( 2.72 mmol / l ) .
sodium chloride supplementation ( 1 mmol / kg / day ) was initiated at 1 week .
she did not require potassium chloride supplementation ( 1 mmol / kg / day ) until 5 months of age when she became persistently hypokalemic ( k 2.9 mmol / l ) .
indomethacin ( 2 mg / kg / day ) was commenced at 1 year of age given for failure to thrive ( height sds 3.7 , weight sds 3.9 ) .
her growth response to indomethacin was appreciable , but less marked than that of her sister .
however , her growth has improved with a gradual increase in the dose to 3 mg / kg / day from 2 years of age ( current height sds 1.96 , weight sds 1.11 ; figure  1 ) .
magnesium glucoheptonate supplementation was also started at 2 years of age ( 3 mg of elemental mg / kg / day ) with the evolution of hypomagnesemia ( serum mg 0.66
she has required multiple admissions to hospital for exaggerated electrolyte imbalances including severe hypokalemia ( k < 2.5 mmol / l ) in association with routine childhood infections .
her uca : cr is now persistently in the hypocalciuric range ( < 0.05 mmol : mmol ) .
her current treatment regime at 5 years of age includes potassium chloride ( 3.8 mmol / kg / day divided bid ) , magnesium glucoheptonate ( 4.7 mg / kg / day of elemental mg divided tid ) , indomethacin ( 3.8 mg / kg / day divided bid ) and amiloride ( 0.8 mg / kg once daily ) .
electrolytes and blood gas have been stable on this regimen ( current na 137 mmol / l , k 3.6 mmol / l , cl 100 mmol / l , mg 0.81 mmol / l , ph 7.4 , hco3 30 mmol / l ) . of note
the most recent serum creatinine was normal at 41 mol / l ( egfr 94 ml / min/1.73 m ) .
genetic testing identified biallelic slc12a3 mutations in both siblings : c.473 g > a encoding p.r158q and c.631_642del ( p.r211_e214del ) ( figure  2 ) .
the c.473 g > a mutation has been previously described in a child with gs   while the c.631_642del mutation has not been previously reported .
the slc12a1 , kcnj1 , clcnka , clcnkb , bsnd genes were also screened with no mutations identified .
the c.473 g > a mutation was found to be maternal in origin and c.631_642del paternal .
the father is of normal height ( 180 cm , sds 0.44 ) ; however , the mother is short ( 150 cm , sds 2.05 ) . 

slc12a3 gene displaying known exons with mutations identified in the cases marked . following the molecular analysis ,
both sisters were electively admitted to hospital to determine prostaglandin ( pge2 ) excretion while off indomethacin therapy .
we felt that this admission would clarify the need for long - term indomethacin therapy in both patients , given this therapy is normally prescribed for cases of bs and carries significant long - term risks of renal and gastrointestinal toxicity .
indomethacin was held for 48 h prior to admission ( washout period ) , but regular supplements were continued in both siblings . upon admission ,
initial bloodwork revealed severe hypokalemia ( 2.5 mmol / l in both ) with metabolic alkalosis ( case 1 : hco3 32 mmol / l , case 2 : hco3 33 mmol / l ) .
both siblings were polyuric upon presentation ( case 1 : 5.5 ml / kg / h , case 2 : 8.8 ml / kg / h ) .
twenty - four - hour urine prostaglandin e2 ( pge2 ) excretion was significantly elevated at 2059 ng / day/1.73 m in case 1 and 3609 ng / day/1.73
m in case 2 ( normal range 48394 ng/24 h/1.73 m ) . after a bolus of normal saline ( 20 ml / kg ) and following 48 h of intravenous fluids ( maintenance rate ) ,
urine pge2 excretion decreased to normal ranges in both siblings ( case 1 : 374 ng/24 h/1.73 m , case 2 : 312 ng/24 h/1.73 m in case 2 ) .
based on these results , a decision was made to reintroduce indomethacin at their previous doses .
it was thought unlikely that the siblings would be able to consume sufficient oral fluids and salt supplementation to replicate the effects of the intravenous volume expansion achieved in hospital .
the polyuria and electrolyte / acid  base derangements again improved within 1 week of restarting therapy .
the classic description of gs is of a benign salt - wasting condition most often diagnosed in adulthood [ 1 , 3 ] .
however , in more recent literature , gs appears to be responsible for a wider spectrum of disease than initially appreciated [ 4 , 19 , 20 ] .
a limited number of reports have emerged describing children affected as early as the neonatal period [ 21 , 22 ] . also mentioned within larger cohort descriptions of gs
are cases presenting at < 2 years of age with symptoms including growth delay , hypotonia and muscular spasms from severe hypomagnesemia [ 4 , 19 , 20 ] .
previous case series have suggested that males may be more severely affected than females . aside from the severity of our described gs cases ,
there are some interesting biochemical findings worthy of discussion , in particular the demonstration of raised urinary pge2 excretion in both siblings . increased pge2
is typically associated with nkcc2 or romk channel mutations resulting in antenatal bs where patients present in the neonatal period with a history of polyhydramnios , prematurity and severe salt wasting .
in contrast , patients with gs tend to have normal pge2 levels as described by lthy et al . .
it has been thought that this discrepancy in pge2 levels explains why children with bs normally require non - steroidal anti - inflammatory drug therapy in addition to salt and fluid supplementation whereas children with gs do not [ 6 , 20 ] .
nonetheless , improved growth in response to indomethacin therapy in gs has been described in the literature [ 21 , 24 ] .
our demonstration of raised urine pge2 level confirms that indomethacin is a rational therapy in patients with more severe salt - wasting phenotypes associated with slc12a3 mutations .
another feature in both patients was the initial absence of hypocalciuria , which has previously been considered a discriminating feature of gs [ 6 , 20 , 25 ] .
more recent case series of patients with slc12a3 mutations have demonstrated variability in urine calcium excretion [ 4 , 23 ] .
interestingly , case 1 demonstrated hypercalciuria upon presentation and case 2 had normal urinary calcium excretion . to our knowledge
thus , we confirm that urinary calcium excretion can not be relied upon as a diagnostic feature in gs and that some patients with initially high or normal urinary calcium excretion will eventually develop hypocalciuria .
we would like to acknowledge some limitations in the genetic analysis of the described cases .
we were unable to perform quantitative or semi - quantitative techniques such as multiplex ligation probe amplification screening .
as a result , it is possible that a large deletion , duplication or rearrangement could have been missed .
also , we did not screen for mutations in the casr given the absence of hypocalcemia and development of hypocalcuria .
in conclusion , given the range of phenotypic expression in the salt - losing tubulopathies , genetic testing is the only method capable of confirming the precise nature of the underlying tubular defect .
previously proposed discriminating features such as urine calcium excretion , hypomagnesemia and age of presentation have all been shown to be variable in gs and may evolve with time as illustrated by our cases . despite this , we would suggest that the identification of slc12a3 mutations should not preclude pediatric patients with a more severe salt - wasting phenotype from a trial of indomethacin .
 our understanding of gitelman syndrome ( gs ) and bartter syndrome has continued to evolve with the use of genetic testing to more precisely define the tubular defects responsible . 
 gs is caused by mutations in the slc12a3 gene encoding the na+cl co - transporter of the distal convoluted tubule ( ncct ) and tends to be associated with a milder salt - losing phenotype . 
 we describe two female siblings presenting in infancy with a severe salt - losing tubulopathy and failure to thrive due to compound heterozygous mutations in the slc12a3 gene encoding the ncct . 
 both children were treated with indomethacin resulting in improved linear growth and polyuria . some atypical biochemical findings in our cases are discussed including raised urinary prostaglandin ( pge2 ) excretion that normalized with intravenous fluid repletion . 