Type III Bartter-like syndrome in an infant boy with Gitelman syndrome and autosomal dominant familial neurohypophyseal diabetes insipidus

We report the case of an infant boy with polyuria and a familial history of central diabetes insipidus. Laboratory blood tests disclosed hypokalemia, metabolic alkalosis, hyperreninemia, and hyperaldosteronism. Plasma magnesium concentration was slightly low. Urine analysis showed hypercalciuria, hyposthenuria, and high excretion of potassium. Such findings oriented toward type III Bartter syndrome (BSIII). Direct sequencing of the CLCNKB gene revealed no disease-causing mutations. The water deprivation test was positive. Magnetic resonance imaging showed a lack of posterior pituitary hyperintensity. Finally, direct sequencing of the AVP-NPII gene showed a point mutation (c.1884G>A) in a heterozygous state, confirming an autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI). This condition did not explain the patient's phenotype; thus, we investigated for Gitelman syndrome (GS). A direct sequencing of the SLC12A3 gene showed c.269A>C and c.1205C>A new mutations. In conclusion, the patient had a genetic combination of GS and adFNDI with a BSIII-like phenotype.