ADPKD in an Elderly Patient with a Novel IFN122 Variant

Introduction: Autosomal Dominant Polycystic Kidney Disease (ADPKD) is typically caused by mutations in PKD1 or PKD2. However, atypical variants are increasingly recognized, especially with expanded genetic testing Case Description: We present the case of an 80-year-old male with a history of ADPKD, chronic kidney disease stage 3a and coronary artery disease status post coronary artery bypass graft x 3. MRI showed significantly enlarged kidneys (right: 3705 cc, left: 4230 cc) , classified as Mayo imaging class 1C, along with multiple hepatic cysts. Urinalysis showed 2+ proteinuria without hematuria. Genetic testing identified a mutation in IFN122 gene. The patient had no family history of intracranial aneurysm or hemorrhage. Despite the marked kidney enlargement, the progression has been relatively slow. Given his age and the uncertain benefit of tolvaptan in non-PKD1/PKD2 mutations, the patient elected not to initiate therapy. Discussion: This case highlights the expanding spectrum of genetic mutations associated with ADPKD. The IFT122 gene encodes a component of the IFT-A complex, which plays a critical role in the ciliary handling of PKD1 and PKD2 proteins. Variants involving IFT122 may result in a less progressive disease course compared to classic PKD1/PKD2 mutations. The role of tolvaptan remains unclear in such variants, particularly in elderly patients. Assessment methods for tolvaptan eligibility include eGFR slope, mean US kidney length, MRI TKV and, more recently, genotype. New algorithms, like the PROPKD score, now incorporate genetic testing to help determine the risk of early onset ESKD; however, current emphasis is mainly on the identification of protein truncating variants of PKD1 or missense mutations in PKD1 or PKD2. All patients should be offered genetic testing as this could inform prognosis as well as eligibility for tolvaptan.The graph provides a visual summary of serum creatinine and eGFR trends over a five-year span