Late onset of familial neurogenic diabetes insipidus in monozygotic twins.

Objective: Autosomal dominant familial diabetes insipidus (FNDI) is a rare disease characterized by polydipsia and polyuria due to deficiency of the antidiuretic hormone, arginine vasopressin (AVP). We report the first Slovak family with the disease. Noteworthy is the concordantly belated debut of the disease symptoms in two monozygotic twin proband girls in the age of 17 years. Because of inconclusive results of water deprivation test consistent with partial diabetes insipidus (DI), missing "bright spot" of posterior pituitary gland in T1-weighted magnetic resonance imaging and family occurrence of polyuria and polydipsia on anamnestic evaluation.

Methods: Molecular genetic testing of the AVP gene was proceeded, because of the inconclusive results of water deprivation test consistent with partial diabetes insipidus, missing "bright spot" of posterior pituitary gland in T1-weighted magnetic resonance imaging and family occurrence of polyuria and polydipsia on anamnestic evaluation.

Results: Genetic analysis revealed a heterozygous g.279G>A substitution that predicts a p.Ala19Thr substitution in the signal peptide of the AVP prohormone. The wide intrafamiliar variations (3 to 17 years) in disease onset together with the concordantly delayed debut of polyuria in two monozygotic twin girls suggest that individual differences in genetic influences family environmental factors may modify the penetrance of the mutation of the AVP gene.

Conclusions: The present paper supports the notion that molecular genetic evaluation should be performed in all patients with familial occurrence of DI regardless of the clinical results.