Objective: Familial autosomal dominant neurohypophyseal diabetes insipidus (FNDI) is a rare form of central diabetes insipidus (DI), which is caused by mutations in the vasopressin-neurophysin II (AVP-NPII) gene. The present study evaluated the AVP secretion over time and analysed the structure of the AVP-NPII gene in a Brazilian family with FNDI.
Subjects and design: Four affected members and one nonaffected member from one Brazilian family with FNDI were studied. The diagnosis of central DI was established by fluid deprivation test and hypertonic saline infusion. Two affected members were assessed twice within a 6-year interval. For molecular analysis, genomic DNA was extracted and the AVP-NPII gene was amplified by polymerase chain reaction.
Results: The functional assessment of patients with FNDI over time confirmed a progressive loss in AVP secretion. Two patients were first diagnosed as partial central DI and, several years later, they developed severe central DI. Sequencing analysis revealed a heterozygous new point mutation in the nucleotide 1892 in the coding sequence for neurophysin-II of the AVP-NPII gene (1892G>C) predicting an amino acid substitution (A68P) in all affected members.
Conclusion: Our data demonstrate a gradual vasopressinergic deficiency due to a novel mutation in the AVP-NPII gene in a Brazilian family with FNDI. The accumulation of A68P mutated precursor might have a cytotoxicity effect, leading to a gradual death of magnocellular neurones, and a progressive decline in AVP secretion.