Family experience with individuals of different ages and clinical presentations diagnosed with DI: do familial DI cases tolerate polyuria better?

Objectives: Familial neurohypophyseal diabetes insipidus (DI) is a rare genetic disorder caused by vasopressin deficiency due to AVP gene mutations. This case report describes the genetic findings and clinical profiles of three generations within a family affected by hereditary central DI and managed with desmopressin.

Case presentation: An 8-month-old male infant was admitted due to persistent polyuria and polydipsia that had been present since birth. History revealed a daily fluid intake of 7,200 mL and required 13 full diapers. The water deprivation test revealed a serum osmolality >300 mOsm/kg with a concurrently low urine osmolality (<300 mOsm/kg), confirming the diagnosis of DI. Desmopressin therapy was initiated for the patient. Using next-generation sequencing, a heterozygous variant c.329G>A (p.Cys110Tyr) was detected in the AVP gene. Following our patient's diagnosis, we evaluated first cousin once removed (on the maternal side) for similar symptoms. Upon identification of the heterozygous AVP variant via next-generation sequencing, desmopressin treatment was started. The same variant was detected in our patient's grandfather, mother, aunt, great-uncle, and first cousin once removed. Polyuria and polydipsia were present in all patients included in our case series. The grandfather and great-uncle, who were initially diagnosed, experienced delayed diagnosis and later developed renal complications. In contrast, the following generations of the family were diagnosed early.

Conclusions: In familial cases, parents are often familiar with the clinical features of DI, allowing them to ensure adequate hydration, manage polyuria, and minimize the risk of dehydration. However, early diagnosis reduces the risk of long-term complications and enables effective family screening, allowing identification of previously unrecognized mild cases.