Clinical features, diagnosis and molecular studies of familial central diabetes insipidus

Background: Familial central diabetes insipidus (DI) is rare and is characterised by polydipsia and polyuria with a variable age of onset. The evaluation of arginine vasopressin (AVP) secretion in these individuals has been reported infrequently and only in adulthood. Objective: To describe the clinical features, diagnosis and molecular investigation of children affected by familial central DI. Methods: Functional studies of AVP secretion were undertaken in children from two kindreds with familial central DI. The AVP-neurophysin II (AVP-NPII) gene was also sequenced in symptomatic individuals. Results: In affected individuals, the result of the water deprivation test may be inconclusive. However, the hypertonic saline test identified both the severe and partial forms of AVP deficiency. A novel mutation of the AVP-NPII gene was identified by direct gene sequencing in both families. Conclusions: This report highlights the progressive decline in AVP secretion with increasing age in this disorder and the usefulness of mutational analysis in these families. In symptomatic individuals, the hypertonic saline test may be a useful second-line investigation for functional studies of AVP secretion where molecular diagnostics are unavailable