A Case Highlighting the Importance of Genetic Testing in Cystic Kidney Diseases

Introduction: Cystic kidney diseases can be hereditary, acquired, or developmental, each exhibiting distinct clinical presentations and pathophysiology. Autosomal dominant polycystic kidney disease (ADPKD) is usually inherited in an autosomal dominant pattern, but 10-25% of cases result from de novo mutations, which can be misdiagnosed as other cystic kidney diseases like tuberous sclerosis complex (TSC) in the absence of systemic signs. Case Description: A 42-year-old male with a history of stage 3b chronic kidney disease (CKD), initially presumed to be secondary to ADPKD diagnosed at age 5 based on magnetic resonance imaging (MRI) findings of bilateral renal cysts, recurrent cyst infections, and hematuria throughout his life. The patient was seen at Northwestern University due to insurance change and inability to follow with prior nephrologist. The patient has no definitive family history of cystic kidney disease. Previous MRI revealed class 1D cysts, though the patient declined tolvaptan treatment. Given the negative family history, genetic testing was performed and returned positive for the TSC2 gene, suggesting a diagnosis of TSC rather than PKD. Subsequent brain MRI revealed a cortical tuber in the left temporal insular region with FLAIR changes. The patient did not have other systemic manifestations of TSC. He was offered treatment with a mammalian target of rapamycin (mTOR) inhibitor but remains hesitant to begin treatment. The patient is being appropriately monitored for systemic manifestations such as cardiac rhabdomyomas, lymphangioleiomyomatosis, hamartomas, and seizures, which can be life-threatening. Discussion: Genetic testing, along with imaging, is essential for diagnosing cystic kidney diseases, supporting accurate diagnosis, management of renal and systemic involvement, and genetic counseling.MRI showing multiple cysts in bilateral kidneys