Familial neurohypophysial diabetes insipidus in a large Dutch kindred: effect of the onset of diabetes on growth in children and cell biological defects of the mutant vasopressin prohormone

A murine model of autosomal dominant neurohypophyseal diabetes insipidus reveals progressive loss of vasopressin-producing neurons

Familial neurohypophyseal diabetes insipidus (FNDI) is an autosomal dominant disorder caused by mutations in the arginine vasopressin (AVP) precursor. The pathogenesis of FNDI is proposed to involve mutant protein-induced loss of AVP-producing neurons. We established murine knock-in models of two different naturally occurring human mutations that cause FNDI. A mutation in the AVP signal sequence [A(-1)T] is associated with a relatively mild phenotype or delayed presentation in humans. This mutation caused no apparent phenotype in mice. In contrast, heterozygous mice expressing a mutation that truncates the AVP precursor (C67X) exhibited polyuria and polydipsia by 2 months of age and these features of DI progressively worsened with age. Studies of the paraventricular and supraoptic nuclei revealed induction of the chaperone protein BiP and progressive loss of AVP-producing neurons relative to oxytocin-producing neurons. In addition, Avp gene products were not detected in the neuronal projections, suggesting retention of WT and mutant AVP precursors within the cell bodies. In summary, this murine model of FNDI recapitulates many features of the human disorder and demonstrates that expression of the mutant AVP precursor leads to progressive neuronal cell loss.

Diabetes insipidus in children: pathophysiology, diagnosis and management

In diabetes insipidus, the amount of water ingested and the quantity and concentration of urine produced needs to be carefully regulated if fluid volume and osmolality are to be maintained within the normal range. One of the principal mechanisms controlling urine output is vasopressin which is released from the posterior pituitary gland and enhances water reabsorption from the renal collecting duct. In diabetes insipidus, the excessive production of dilute urine, and the causes of this clinical picture can be divided into three main groups: the first is primary polydipsia where the amount of fluid ingested is inappropriately large; the second group is cranial diabetes insipidus where the production of vasopressin is abnormally low; and, the third group is nephrogenic diabetes insipidus where the kidney response to vasopressin is impaired. The history and examination may suggest an underlying explanation for diabetes insipidus but a range of baseline and more extensive investigations may be required before a diagnosis can be reached. These investigations are not without risk, and the results need to be interpreted carefully because children do not always segregate neatly into a particular diagnostic category on the basis of one test alone. Children with cranial diabetes insipidus typically respond to arginine vasopressin or its manufactured analogue, desmopressin, with an increase in urine osmolality and an associated reduction in urine output. Such children usually require neuroimaging to look for evidence of evolving CNS pathology, such as an intracranial tumour. Vasopressin "replacement" with desmopressin is the treatment of choice in patients with cranial diabetes insipidus although extreme caution is required when treating babies or small children because of the danger of fluid overload. Abnormal production of other pituitary hormones in children with CNS disease can also influence fluid balance. Nephrogenic diabetes insipidus can be due to abnormal electrolyte concentrations, therefore these should be measured as part of the initial assessment. In a small number of children the defect is a primary abnormality of the vasopressin receptor or one of the water channel proteins (aquaporins) involved in water transport. The treatment of these patients is difficult and typically involves therapy with a diuretic such as chlorothiazide, as well as indomethacin. These agents enhance urine osmolality by their effect on circulating volume and renal solute and water handling. The fluid intake of most young children with primary polydipsia can be safely reduced to a more appropriate level.