X-Linked Nephrogenic Diabetes Insipidus Associated with the AVPR2 c.964C>T (p.Pro322Ser) Variant: A Family Case Series.

Background: Nephrogenic diabetes insipidus (NDI) is a rare disorder characterized by renal resistance to arginine vasopressin, most commonly caused by pathogenic variants in the AVPR2 gene. While X-linked NDI classically affects males, heterozygous females may exhibit variable clinical expression. Certain AVPR2 variants are associated with partial NDI and milder phenotypes. Methods: We conducted a retrospective family study of a multigenerational Greek pedigree with suspected hereditary NDI. Clinical, biochemical, and pedigree data were collected through chart review and family interviews. Genetic analysis was performed using whole-exome sequencing, and variant interpretation followed ACMG/AMP guidelines. Results: Fourteen individuals across four generations were evaluated. Molecular analysis identified a familial AVPR2 (NM_000054.7):c.964C>T (p.Pro322Ser) missense variant in three males and three females, with obligate carrier status inferred in two deceased females, segregating in an X-linked pattern. Hemizygous males exhibited a broad phenotypic spectrum, ranging from partial NDI with later onset to severe early-onset disease with urinary tract complications. Heterozygous females showed variable expression, from asymptomatic carriers to mildly symptomatic individuals. The variant co-segregated with disease and, based on ACMG criteria, it was classified as pathogenic. Conclusions: In our family, the AVPR2 c.964C>T (p.Pro322Ser) variant was associated with a remarkably broad clinical spectrum, ranging from asymptomatic heterozygous females to severe early-onset disease with urinary tract complications in affected males. These observations emphasize the need for early molecular diagnosis, systematic evaluation of female carriers, and long-term surveillance to prevent disease-related complications and optimize genetic counselling.