Atypical Bartter syndrome with sensorineural deafness with G47R mutation of the β-subunit for CIC-Ka and CIC-Kb chloride channels, Barttin

Bartter syndrome comprises several related renal tubular disorders including classic Bartter, infantile Bartter (IBS), and Gitelman syndrome. A new distinct group in Bartter syndrome accompanied by sensorineural deafness (BSND) has been identified among the IBS patients. Recently a gene encoding an essential beta-subunit for ClC chloride channels, named barttin, with several mutations of the gene as the cause of BSND, has been described. We have observed a male who had not been diagnosed as Bartter syndrome until 28 yr because of a mild clinical manifestation. The patient was affected with congenital deafness, which urged us to analyze his gene for barttin, and a mutation G47R, which was previously reported, has been identified. However, the clinical feature in the patient lacking the characteristic symptoms of IBS such as polyhydramnios, premature labor, or severe salt loss in neonatal period contrasts with that of the typical BSND patients described so far in the literature. This might be due to a less severe loss of function of barttin induced by G47R mutation, compared with others, and our observation seems to suggest a possibility of the prevalence of mild form BSND with various levels of barttin dysfunction among patients with congenital deafness of unknown origin.