Autosomal dominant polycystic kidney disease (ADPKD), caused by mutation in PKD1 or
PKD2, is usually an adult-onset disorder but can rarely manifest as a neonatal disease
within a family characterized by otherwise typical ADPKD. Coinheritance of a hypomorphic
PKD1 allele in trans with an inactivating PKD1 allele is one mechanism that can cause early
onset ADPKD. Here, we describe two pedigrees without a history of cystic kidney disease
that each contain two patients with onset of massive PKD in utero. The presentations were …