Vasopressin secretion in the DIDMOAD (Wolfram) syndrome

The diabetes insipidus which accompanies the DIDMOAD (Wolfram) syndrome is thought to be hypothalamic in origin, though no formal study of vasopressin secretion in the syndrome has been published, and some data in the literature suggest a renal tubular defect. We have studied vasopressin secretion in seven patients with the Wolfram/DIDMOAD syndrome during three dynamic stimuli: an osmotic stimulus (hypertonic saline infusion), hypoglycaemia (insulin tolerance test) and a baroregulatory stimulus (trimetaphan infusion). Hypertonic saline infusion demonstrated three patients to have complete and four to have partial hypothalamic diabetes insipidus; administration of (per nasal) desmopressin excluded nephrogenic diabetes insipidus in all seven patients. Insulin hypoglycaemia failed to stimulate vasopressin release, but trimetaphan-induced hypotension produced significant though subnormal rises in plasma vasopressin in three patients with partial diabetes insipidus, though it produced a negligible rise and no rise in plasma vasopressin in two patients with complete diabetes insipidus. The data suggest a much greater frequency of hypothalamic diabetes insipidus in the Wolfram/DIDMOAD syndrome than is reported, but did not identify nephrogenic diabetes insipidus. The absence of vasopressin responses to non-osmotic stimuli in patients with complete diabetes insipidus suggests global lack of vasopressin secreting neurones, rather than an isolated osmoreceptor defect or selective vasopressin secreting neuronal loss, as the lesion producing diabetes insipidus in the DIDMOAD syndrome.