Medullary sponge kidney (MSK) disease is a nephropathy characterized by the association of tubular ectasia of precalyceal ducts with sporadic cystic development, multiple renal stones, and/or nephrocalcinosis (calcification of renal parenchyma) and frequently tubular acidification defect. In most cases, both kidneys are affected. The prevalence of MSK in the general population is still unknown. In particular, some patients may develop tubular ectasia without recurrent kidney stone formation; thus, they can remain undiagnosed. Among kidney stone formers, a condition reaching up to 10% of the general population, MSK prevalence is >8%.1 Patients affected by MSK are at risk to form recurrent renal stones, responsible for renal colic and multiple urological interventions. Nevertheless, chronic kidney disease (CKD) is rarely reported. Many patients affected by MSK complain on chronic flank pain, even in the absence of patent renal colic.2 It has been hypothesized that MSK could have a genetic basis. Currently, only a few cases clustering in family have been reported, suggestive of incomplete penetrance. MSK has been associated with various malformations, such as those observed in Beckwith-Wiedemann syndrome with renal developmental defects. Hepatic diseases, such as Caroli disease, responsible for biliary duct dilation, have been described.3 The GDNF, a ligand of RET, allows ureteric bud branching and invasion of the metanephric blastema with the collecting ducts and upstream kidney formation. Recently, GDNF variants have been identified in patients with MSK, supporting the idea that MSK might result from precalyceal and collecting duct development defects.4 Considering the potential genetic origin of MSK, a whole-exome sequencing was proposed in 2 adult patients affected by MSK with CKD, an uncommon condition of MSK.