HNF1B and cystic kidney disease: In further support of a gene–dosage effect, several authors reported unusually early and severe disease, often mimicking renal manifestations of recessive PKD, in patients with either biallelic abnormalities of PKD1 or PKD2, such as our patient [1, 7, 8], or a pathogenic mutation of PKD1 or PKD2 in association with a mutation in another gene associated with renal cystic disease, such as PKHD1 or HNF1β [9].