AQP2 and nephrogenic diabetes insipidus: In particular, age-associated nephrogenic diabetes insipidus in some inbred mouse strains [52, 53] and WAG/Rij rats [54] are caused by an age-progressive decline of AQP2 suggesting that progranulin deficiency may lead to similar but premature AQP2 losses and hence, early manifestations of kidney aging.