Renal dysfunction and barttin expression in Bartter syndrome Type IV associated with a G47R mutation in BSND in a family.

Bartter syndrome (BS) Type IV, associated with a G47R mutation in the BSND gene, is known to result in a mild renal phenotype. However, we report here on three brothers with varying degrees of renal dysfunction from mild to end-stage renal disease associated with renal barttin and ClC-K expression. The brothers had histories of polyhydramnios, prematurity, polyuria, deafness, and small body size. Laboratory findings showed hypokalemic metabolic alkalosis, normotensive hyperreninemic hyperaldosteronism, and an increased urinary excretion of sodium, potassium and chloride, consistent with BS Type IV. Microscopic examination of renal tissue showed hyperplasia of cells at the juxtaglomerular apparatus with dilated atrophic tubules and tubulointerstitial fibrosis. A weak barttin signal related to CIC-K expression in the cytoplasm of tubule cells, but not the basement membrane, was noted. A sequence analysis of the BSND gene showed that the affected males were homozygous for a missense G47R mutation in exon 1 of BSND. These findings suggest that the G47R mutation results in a dramatic decrease in barttin expression, which appears to be related to the location of CIC-K being changed from the basement membrane to the cytoplasm in the tubule and might have varying effects on renal function associated with factors other than this gene.