Plasma Vasopressin in Hereditary Cranial Diabetes Insipidus

ABSTRACT A family comprising 46 members of 4 generations is described; 21 members suffered from incomplete diabetes insipidus (DI) of central origin. The pedigree showed a dominantly transmitted condition. The onset is gradual and starts in early infancy. The clinical symptoms are highly variable and decline in the sixth decade. Plasma vasopressin (AVP) during water deprivation was significantly lower in the DI group than in the controls (4.2±0.5 vs. 10.6±1.7 ng/l) (p 3:1 in the control group (p<0.001). In two affected females, addition of a nonosmotic stimulus caused no increase in plasma AVP. The findings are consistent with a partial defect in the production or release of AVP and not with a dysfunction of the intracranial osmoreceptors. The variable features of incomplete DI indicate that to define the condition by excessive urinary output alone is insufficient. The ratio between urine and serum osmolalities after an appropriate osmotic stimulus together with plasma AVP measurements may be necessary to confirm the diagnosis.