Although we must acknowledge the confounding PKD1 variant in the 25-yo patient from Family 2 as a contributing cause of her cystic kidney disease, we present evidence that CC2D1A is also a contributing factor and could plausibly explain such a severe kidney phenotype at such an early age, as most patients with dominant PKD1 variants present as adults. The gene discussed is PKD1; the disease is cystic kidney disease.