International Journal of Pediatrics found in some patients despite low plasma osmolality is not clear. Nevertheless, this residual and relatively low AVP secretion should have only a weak action on the V2R mutants given their low aﬃnity for AVP and, mainly, the reduced cAMP production level observed after stimulation by AVP. [11]. 4. Diagnosis of NSIAD Patients When NSIAD is suspected, the plasma sodium level, plasma and urine osmolalities, and plasma AVP level should all be measured at the same time during the hyponatremic episode. The association of hyponatremia with relatively high urine osmolality and a low or undetectable plasma AVP level is an indication for sequencing the AVPR2. In siblings, a water- load test can be performed in an asymptomatic boy but cautiously: for example, with only 10 mL/kg of water [5]. In girls, a 20 mL/kg water-load test can help to determine their ability to dilute their urine, as this is variable in heterozygous females due to random X inactivation and will help in providing them with recommendations for water intake. Assessment of the concentration of the plasma von Willebrand factor (vWF) antigen, which is known to be increased by AVP stimulation of the so-called “extrarenal V2R,” does not seem to be helpful in diagnosing NSIAD patients [4]. 5. Management of Patients with NSIAD In symptomatic NSIAD patients with hyponatremia, rapid management with ﬂuid restriction and, if necessary, admin- istration of 30–50% oral urea solution, is necessary to avoid persistent or increased hyponatremia, which carries the risk of brain damage [9, 16]. In addition, hemizygous boys have to avoid massive water intake, as shown by the results observed during water-load testing. In these patients, caution is particularly important when environmental factors may encourage sharp rises in water intake (sports activities, during heat waves, in the summertime, etc.). However, boys bearing the mutation are mainly at risk of developing severe hyponatremia during infancy when their water intake is mostly under parental control. In heterozygous females, the advice will depend on the results of the water-load test and will range from normal to cautious water or ﬂuid intake. 6. Conclusion The prevalence of this recently recognized disease is diﬃcult to determine in children, and adults. Although NSIAD does not seem to have an early neonatal expression, the diagnosis should systematically be considered in infants, children and adults presenting with hyponatremia associated with high urine osmolality. In males, the diagnosis will be easily made by sequencing the AVPR2. In siblings, a water-load test can be helpful in studying and advising female carriers. 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