Serial MR intensity changes of the posterior pituitary in patients with diabetes insipidus after transsphenoidal surgery for pituitary adenomas: report of two cases

[Central diabetes insipidus after resection of sellar-suprasellar tumors: prevalence and predictors of manifestation]

Central diabetes insipidus is a neuroendocrine disorder caused by disturbances in antidiuretic hormone release. The last one is responsible for fluid and electrolyte balance regulation. The most common cause of diabetes insipidus is resection of sellar-suprasellar tumors followed by damage to hypothalamic nuclei responsible for antidiuretic hormone release, disruption of antidiuretic hormone transportation from hypothalamus or its release by neurohypophysis. According to various data, postoperative diabetes insipidus occurs in 13-30% of cases. The highest risk of diabetes insipidus is observed after resection of craniopharyngioma, Rathke's cleft cyst and ACTH-releasing pituitary microadenoma. This review is devoted to prevalence and predictors of diabetes insipidus after resection of sellar-suprasellar tumors.

Identification, characterization and rescue of a novel vasopressin-2 receptor mutation causing nephrogenic diabetes insipidus

OBJECTIVE

X-linked nephrogenic diabetes insipidus (XNDI), caused by mutations in the V2 vasopressin receptor (V2R), is clinically distinguished from central diabetes insipidus (CDI) by elevated serum vasopressin (AVP) levels and unresponsiveness to 1-desamino-8-d-arginine vasopressin (DDAVP). We report two infants with XNDI, and present the characterization and functional rescue of a novel V2R mutation.

PATIENTS

Two male infants presented with poor growth and hypernatraemia. Both patients had measurable pretreatment serum AVP and polyuria that did not respond to DDAVP, suggesting NDI. However, both also had absent posterior pituitary bright spot on MRI, which is a finding more typical of CDI.

METHODS

The AVPR2 gene encoding V2R was sequenced. The identified novel missense mutation was re-created by site-directed mutagenesis and expressed in HEK293 cells. V2R activity was assessed by the ability of transfected cells to produce cAMP in response to stimulation with DDAVP. Membrane localization of V2R was assessed by fluorescence microscopy.

RESULTS

Patient 1 had a deletion of AVPR2; patient 2 had the novel mutation L57R. In transiently transfected HEK293 cells, DDAVP induced detectable but severely impaired L57R V2R activity compared to cells expressing wild-type V2R. Fluorescence microscopy showed that myc-tagged wild-type V2R localized to the cell membrane while L57R V2R remained intracellular. A nonpeptide V2R chaperone, SR121463, partially rescued L57R V2R function by allowing it to reach the cell membrane.

CONCLUSIONS

L57R V2R has impaired in vitro activity that can be partially improved by treatment with a V2R chaperone. The posterior pituitary hyperintensity may be absent in infants with XNDI.