Inheritance: X-linked (90%), autosomal recessive (9%), autosomal dominant (1%)
Genes and proteins:
(1) AVPR2 (X-linked) on Xq28, producing vasopressin V2 receptor
(2) AQP2 (autosomal dominant or autosomal recessive) on 12q13 producing aquaporin 2
The X-linked form is typically seen in males. The autosomal dominant form would show a definite familial inheritance pattern.
Clinical features:
(1) polyuria
(2) excessive thirst with polydipsia
(3) tendency to become easily dehydrated
(4) poor feeding and failure to thrive
(5) short stature
(6) dilatation of the urinary bladder (megacystitis) and ureters (hydroureter)
Laboratory features:
(1) dilute urine (very low osmolarity)
(2) presence of antidiuretic hormone (ADH, arginine vasopressin)
Diagnosis is confirmed by demonstrating a mutation in the responsible genes.
It is important to exclude acquired forms of nephrogenic DI and central DI.
