Distal renal tubular acidosis and high urine carbon dioxide tension in a patient with southeast Asian ovalocytosis.
Southeast Asian ovalocytosis (SAO) is the best-documented disease in which mutation in the anion exchanger-1 (AE1) causes decreased anion (chloride [Cl-]/bicarbonate [HCO3-]) transport. Because AE1 is also found in the basolateral membrane of type A intercalated cells of the kidney, distal renal tubular acidosis (dRTA) might develop if the function of AE1 is critical for the net excretion of acid. Studies were performed in a 33-year-old woman with SAO who presented with proximal muscle weakness, hypokalemia (potassium, 2.7 mmol/L), a normal anion gap type of metabolic acidosis (venous plasma pH, 7. 32; bicarbonate, 17 mmol/L; anion gap, 11 mEq/L), and a low rate of ammonium (NH4+) excretion in the face of metabolic acidosis (26 micromol/min). However, the capacity to produce NH4+ did not appear to be low because during a furosemide-induced diuresis, NH4+ excretion increased almost threefold to a near-normal value (75 micromol/L/min). Nevertheless, her minimum urine pH (6.3) did not decrease appreciably with this diuresis. The basis of the renal acidification defect was most likely a low distal H+ secretion rate, the result of an alkalinized type A intercalated cell in the distal nephron. Unexpectedly, when her urine pH increased to 7.7 after sodium bicarbonate administration, her urine minus blood carbon dioxide tension difference (U-B Pco2) was 27 mm Hg. We speculate that the increase in U-B Pco2 might arise from a misdirection of AE1 to the apical membrane of type A intercalated cells.
Kaitwatcharachai
C
C
Renal and Medical Molecular Biology Units, Songklanakarin Hospital, Bangkok, Thailand.
Vasuvattakul
S
S
Yenchitsomanus
P t
Pt
Thuwajit
P
P
Malasit
P
P
Chuawatana
D
D
Mingkum
S
S
Halperin
M L
ML
Wilairat
P
P
Nimmannit
S
S
D000141:Acidosis, Renal Tubular / Q000209:etiology* / Q000378:metabolism / Q000652:urine; D000328:Adult; D017920:Antiporters / Q000235:genetics; D002245:Carbon Dioxide / Q000652:urine*; D004232:Diuretics / Q000008:administration & dosage; D004612:Elliptocytosis, Hereditary / Q000150:complications*; D005260:Female; D005665:Furosemide / Q000008:administration & dosage; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000644:Quaternary Ammonium Compounds / Q000652:urine; D017693:Sodium Bicarbonate / Q000008:administration & dosage
D017920:Antiporters; D004232:Diuretics; D000644:Quaternary Ammonium Compounds; D002245:Carbon Dioxide; D005665:Furosemide; D017693:Sodium Bicarbonate