PKD1 and cystic kidney disease: We suggest that: 1) the PKD2 p.(Cys331Thr) variant is pathogenic, since it is de-novo in a patient with a renal cystic disease and is transmitted to both fetuses; 2) the p.(Ser123Thr) variant in PKD1 is hypomorphic, since it does not cause renal disease in the father (age 44 years), but worsens the renal phenotype when co-inherited with a PKD2 mutation; 3) the missense variant p.(Arg872Gly) in PKD2, already described as disease-causing in HGMD database (Neumann et al., 2013), is likely benign, since it is present in a healthy man and does not segregate with disease in the fetuses.