Molecular biology techniques have begun to shed light on the genetic basis of autosomal dominant central DI, but several very basic questions remain to be answered. The disorder was initially presumed to have a developmental, degenerative, or autoimmune basis based on the autopsy findings in the hypothalamus of a limited number of patients. The molecular cloning of the AVP-NP II gene and the clue from the Brattleboro rat that at least this one form of hereditary DI involved an AVP-NP II gene mutation allowed us to focus on this gene in our study of human hereditary DI. Our initial experiments did not show this gene to have a major structural alteration such as a deletion, insertion, or rearrangement, but the approach was not capable of detecting more suitable defects. The linkage studies provided substantial evidence that one particular OT-NP I haplotype was linked to the disease phenotype in each family, and thus, a mutation in the AVP/OT region of chromosome 20 is responsible for this disease. Ito et al. (1991) then identified a single base change in the AVP-NP II gene in affected members of one Japanese family. This change was not detected in unrelated, unaffected persons and thus is a good candidate for the mutation causing the disease in this family. However, there appears to be diversity in the molecular basis of autosomal dominant central DI as affected members of one of our families did not have this particular base change in either AVP-NP II allele and recently another distinct AVP-NP II gene base change has been associated with this disorder. One interesting question still to be addressed is how a mutation in the NP-II coding region of this gene prevents AVP release from the posterior pituitary in the rat or the human disease. Does the disrupted AVP-NP II coding sequence prevent normal processing of the mRNA so that it can not be properly translated into protein? Does the mutated AVP-NP II glycoprotein precursor protein interfere with normal post-translational processing to prevent release of AVP? Is an altered NP II protein not able to protect the AVP from proteolysis within the magnocellular neuron? An even more puzzling question is how a mutation in the gene encoding a hormone is inherited in an autosomal dominant pattern. The Brattleboro rat model follows the a priori expectation of autosomal recessive inheritance: the animal only exhibits a defect in hormone function if both genes encoding the hormone are defective.(ABSTRACT TRUNCATED AT 400 WORDS)