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renal tubular acidosis is considered when a relatively normal glomerular filtration rate is associated with metabolic acidosis , hyperchloremia and a normal plasma anion gap .
distal renal tubular acidosis ( drta ) is characterized by an impairment of net acid secretion by the distal tubule and may be associated with hypokalaemia ( type i ) or hyperkalemia ( type iv ) .
. it can be either inherited , idiopathic or acquired secondary to a variety of conditions [ 1 , 2 ] .
for example , autosomal dominant or recessive mutations in the anion exchanger 1 ( ae1 ) gene encoding the erythroid and kidney anion exchanger 1 ( chloride - bicarbonate ) may result in drta with ovalocytosis or spherocytosis in patients from southeast asia .
the most common causes of secondary drta are autoimmune disorders such as systemic lupus erythematosus , sjgren 's syndrome   and primary biliary cirrhosis . of note ,
primary sclerosing cholangitis ( psc ) is often compared to primary biliary cirrhosis , but no psc - associated drta has been previously reported .
we report a case of type i drta occurring during the course of psc that was corrected by a successful liver transplantation .
a 26-year - old lao - thai male patient with uneventful previous medical records was diagnosed as severe ( child score b7 , model for end - stage liver disease ( meld ) score 24 ) hepatic cirrhosis secondary to psc in august 2012 .
biliary magnetic resonance imaging revealed an irregular aspect of intrahepatic bile ducts with alternance of stenosis and dilatation ( similar to a 
liver biopsy showed mild inflammation in the portal spaces and major cholestasis in hepatocytes and bile ducts , with no sign of suppurated cholangitis , obliteration , or cholangiocarcinoma .
anti - mitochondrial , anti - smooth muscle , anti - liver cytosol , anti - endoplasmic reticulum , anti - neutrophil cytoplasmic and anti - nuclear antibodies were negative .
no inflammatory bowel disease was detected . during the following months he developed a marked hypokalaemia resistant to potassium replacement therapy , followed by metabolic acidosis . at referral to the renal department he had severe jaundice , generalized muscle weakness and bone pain .
body mass index was 22.3 kg / m and blood pressure was 110/70 mmhg with no sign of volume depletion .
metabolic acidosis [ arterial ph 7.34 , partial pressure of carbon dioxide ( pco2 ) 27 mmhg , bicarbonatemia 15
mmol / l ] was associated with hyperchloremia ( 117 mmol / l ) , a normal plasma anion gap [ 17.6 mmol / l ( normal 16  4 mmol / l ) ; 18.1 mmol / l after correction for albumin , albuminemia 38
g / l ) , a positive urinary anion gap ( 7.6 mmol / l ) and an inappropriate urinary ph of 6 . hypokalaemia ( 2.7
mmol / l ) was associated with a normal electrocardiogram , inadapted renal potassium loss ( urinary potassium excretion 88 mmol / day ) , normal blood magnesium ( 1.0 mmol / l ) , increased plasma renin activity ( 188 pg / ml ) and normal aldosterone level ( 13 ng / dl ) .
urinalysis showed urinary sodium at 39 mmol / l ( fractional excretion of sodium 1.3% ) , moderate proteinuria ( protein : creatinine ratio 650 mg / g , urinary albumin : creatinine ratio 50 mg / g ) , calcium : creatinine ratio of 10.7 mmol / g and the absence of glycosuria , aminoaciduria , inappropriate phosphaturia , leukocyturia and haematuria .
liver investigations showed severe cholestasis with a total bilirubin value of 831 mol / l ( normal
< 21 mol / l ) , mainly conjugated [ 762 mol / l ( normal
blood cell count was indicative of regenerative normocytic anaemia ( haemoglobin 9.5 g / dl , mean cell volume 82 fl , reticulocytes 119.000/mm ) , thrombocytosis ( 456.000/mm ) and leukocytosis ( 11.670/mm ) .
heterozygous beta thalassemia [ haemoglobin ( hb ) a 93.0% , hb a2 6.0% , hb f < 1% ] was demonstrated by electrophoresis .
testing for scl4a1 gene mutation , commonly associated with drta in the southeast asian population , was negative .
, the urine to blood pco2 gradient did not rise normally ( i.e. > 30 mmhg when bicarbonaturia approaches 80 meq / l ) , indicative of a low rate of h secretion [ 7 , 8 ] . in the present case ,
the maximal urine to blood pco2 gradient at bicarbonaturia of 80 meq / l was 1.2 mmhg while urinary ph and pco2 were 7.1 and 33 mmhg , respectively .
the opportunity of liver transplantation was taken and the patient was transplanted in july 2013 , before a furosemide - fludrocortisone test and a kidney biopsy were performed .
as shown in figure  1 , hypokalaemia and acidosis disappeared upon correction of bilirubinemia .
a mild and stable increase in serum creatinine ( 130 mol / l ) without proteinuria ( proteinuria : creatininuria ratio 50 mg / g ) occurred about 1 month later and was attributed to calcineurin inhibitor toxicity .
a fludrocortisone - furosemide test was normal 6 months after liver transplantation with normal urinary acidification and urinary ph of 4.77 . 

1.improvement in distal renal tubular acidosis - associated disorders ( metabolic acidosis and hypokalaemia ) was concomitant with the decrease in total bilirubin following liver transplantation .
improvement in distal renal tubular acidosis - associated disorders ( metabolic acidosis and hypokalaemia ) was concomitant with the decrease in total bilirubin following liver transplantation .
to our knowledge , this is the first described case of type i drta associated with psc .
interestingly , renal tubular dysfunction was corrected by liver transplantation . since the patient originated from laos , an inherited mechanism 
this gene encodes for anion exchanger 1 ( ae1 ) , a bicarbonate / chloride transporter localized in both red cell membrane and basolateral membrane of the collecting tubule alpha - intercalated cell .
its mutations are common in southeast asia and result in drta and ovalocytosis , which can occur in adulthood .
two other mutations in genes encoding for the 4 ( atp6v0a4 ) and 1 ( atp6v1b1 ) subunits of the v - atpase of the alpha - intercalated cells of the collecting duct can also cause hereditary drta .
we did not perform gene sequencing for these genes because the onset of the disease occurs in childhood ( atp6v0a4 ) and is associated with sensorineural deafness ( atp6v1b1 ) .
moreover , altered urinary acidification could not be attributed to impaired distal sodium delivery , as fractional excretion of sodium was not low .
, the ion disturbances of drta were corrected in this patient a few weeks after liver transplantation with immunosuppressive therapy .
sjgren 's syndrome is associated with drta , and several reports suggest that autoantibodies against carbonic anhydrase ii enzyme   or vacuolar h - atpase pump in the collecting duct   are involved in the pathogenesis of drta . in a recent unusual case of multiorgan autoimmunity , circulating autoantibodies directed against intercalated cells were apparently involved in the pathogenesis of drta .
primary biliary cirrhosis is an autoimmune liver disease associated with drta and tubulointerstitial nephritis that is alleviated by steroid therapy .
however , psc is not considered an autoimmune disease , but rather an inflammatory condition .
male predominance , lack of a defined pathogenic autoantigen and the potential role of the innate immune system suggest that it may be due to dysregulation of immunity .
although frequently overlooked , bilirubin is a recognized renal toxin , and in the present case bilirubin levels were normalized concomitant to the correction of drta .
recently reported the case of an adult kidney recipient who developed a malignant cholangiocarcinoma 4 years after transplantation and progressively lost transplant function in parallel with a continuous increase in bilirubinemia .
kidney biopsy showed bile thrombi in dilated tubules and bile granules in the cytoplasm of tubular epithelial cells , but no interstitial inflammation . because the patient had no jaundice - associated confounding factor such as sepsis , heart failure or hepatorenal syndrome that could explain his kidney failure
, the authors suggested that bilirubin per se should be seen as a cause of acute tubular necrosis .
van slambrouck et al .   studied 41 autopsies and 3 renal biopsies in 44 jaundiced patients with acute kidney injury .
bile casts were observed 24 times , with involvement of distal nephron segments in 18 mild cases and extension to proximal tubules in 6 more severe cases and they proposed the term bile cast nephropathy .
reported a 49-year - old man with progressive obstructive jaundice secondary to psc who developed acute anuric renal failure requiring prolonged haemodialysis .
renal biopsy showed evidence of tubular epithelial toxicity , pigmented casts , interstitial fibrosis and ischaemic glomerular changes .
after orthotopic liver transplantation , there was an immediate urine output recovery , followed by gradual improvement in renal function to a serum creatinine nadir of 210 mol / l . in the present case ,
liver transplantation also permitted correction of drta biological abnormalities . since kidney biopsy was not performed , whether interstitial inflammation or bile granules in the cytoplasm of distal tubular epithelial cells participated in drta can not be confirmed . in conclusion , to the best of our knowledge , this case report is the first description of type i drta associated with psc .
it illustrates the putative immunological as well as toxic bilirubin - associated mechanisms that may link both entities and reminds us that distal tubular renal function should be carefully assessed in psc patients with acid  base or electrolyte disorders .
we describe the first case of distal renal tubular acidosis ( drta ) associated with primary sclerosing cholangitis . a 26-year - old lao - thai male patient presented with severe jaundice , metabolic acidosis and hypokalaemia . 
 he was diagnosed of drta . 
 liver transplantation resulted in correction of electrolyte disturbances and hyperbilirubinaemia . 
 a fludrocortisone - furosemide test revealed normal urinary acidification , demonstrating no residual drta . 
 this observation suggests that drta may be an early manifestation of bilirubin - associated nephropathy or the consequence of an immune mechanism .