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.


CONCLUSIONS
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.
Lin
Chien-Ming
CM
Department of Pediatrics, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan.
Tsai
Jeng-Daw
JD
Lo
Yi-Fen
YF
Yan
Ming-Tso
MT
Yang
Sung-Sen
SS
Lin
Shih-Hua
SH
D000293:Adolescent; D018118:Chloride Channels / Q000235:genetics*; D018450:Disease Progression; D006801:Humans; D007008:Hypokalemia / Q000235:genetics; D007676:Kidney Failure, Chronic / Q000235:genetics*; D008297:Male; D020125:Mutation, Missense / Q000235:genetics; D017354:Point Mutation / Q000235:genetics*; D028021:Sodium-Potassium-Chloride Symporters / Q000235:genetics*; D064466:Solute Carrier Family 12, Member 1; D013577:Syndrome
C412733:CLCNKB protein, human; D018118:Chloride Channels; C578714:SLC12A1 protein, human; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1