A novel mutation in the renal V2 receptor gene in a boy with trisomy 21.

We describe for the first time an infant with Down syndrome and congenital nephrogenic diabetes insipidus (NDI). The 11-day-old Japanese boy was admitted with failure to thrive and fever. Polyuria (3,000-3,500 ml/m(2) per day), low urine specific gravity (1.001-1.002), and high plasma arginine vasopressin (AVP) (18.2 pg/ml) suggested NDI. Gene analysis confirmed the diagnosis of congenital NDI due to a novel mutation of the V2 receptor gene (L309P). He also had symptoms of Down syndrome and karyotype analysis of the peripheral lymphocytes revealed trisomy 21. The relationship between pyelectasis and a risk of Down syndrome is discussed.