Clinical exome sequencing uncovers an unsuspected diagnosis of Bartter syndrome type 2 in a child with incidentally detected nephrocalcinosis

Nephrocalcinosis is a characteristic feature of both type 1 and type 2 Bartter syndrome. Bartter syndrome type 2 presents antenatally and very early in life. Late-onset presentation with isolated nephrocalcinosis is extremely rare. We describe an 11-year-old girl with incidentally detected medullary nephrocalcinosis on renal ultrasonography. She was clinically suspected to have primary hyperoxaluria based on high urine oxalate. However, clinical exome sequencing revealed a pathogenic missense variant in the KCNJ1 gene leading to the molecular diagnosis of Bartter syndrome type 2. Both parents were heterozygous carriers of the same variant. Subsequent investigations did reveal a mild Bartter syndrome phenotype with mild metabolic alkalosis, high urine chloride and high renin and aldosterone. Our case illustrates phenotypic heterogeneity of Bartter syndrome type 2 and the usefulness of genetic testing in establishing the correct diagnosis and guiding further management in such cases.