P0059CLINICAL AND IMAGING FEATURES OF A NOVEL DNAJB11 MUTATION COMPARED TO PKD1-PKD2 ADULT POLYCYSTIC KIDNEY DISEASE (ADPKD). TWO DIFFERENT DISEASES?
Authors: Manenti Lucio , Pisani Isabella , Allinovi Marco , Gentile Micaela , Farina Maria Teresa , Peyronel Francesco , Zanelli Paola , Sebastio Paola , Palazzo Viviana , Giglio Sabrina , Giuliotti Sara , Fiaccadori Enrico 
Published: June 2020

Abstract

Background and Aims
ADPKD is characterized by the progressive development of bulky renal cysts, often resulting in end-stage renal disease (ESRD). Among this group 85% of cases recognize a genetic mutation concerning PKD1/PKD2 genes (ADPKD). Among the remaining 15% of ADPKD patients, DNAJB11 mutations (DNAJB11-PKD) has been recently recognized. [Cornec-Le Gall E, Olson RJ, Beesse W t al. Monoallelic Mutations to DNAJB11 Cause Atypical Autosomal-Dominant Polycystic Kidney Disease. Am Journ Hum Gen 2018, 102:832-844.]
DNAJB11 encodes a co-chaperone of the endoplasmic reticulum (ER) also called ERdj3. It is part of the HSP40 protein family and plays a central role in both intracellular and extracellular proteomic homeostasis (proteostasis). In the intracellular compartment it acts as a co-chaperone in the pathway of the unfolded protein response (UPR) in which it binds misfolded proteins which have to be secreted and activates BiP an HSP70 of ER whose function is to correct the misfolding. In our Nephrology Unit we collected the largest cohort of patients with a new stop codon mutation (p.Arg34*) of DNAJB11. All patients are relatives of different ranks and were born in a small village in the mountains of the Parma province.In this study we compare clinical features of DNAJB11-PKD with ADPKD to define differences between the two groups.

Method
We identified retrospectively from outpatient and dialysis databases of the Nephrology Unit of Parma patients carrying pArg34* DNAJB11 or PKD1-PKD2 mutations. We collected the clinical features and the available diagnostic imaging of all identified patients.

Results
We collected 19 patients with DNAJB11-PKD and 37 with ADPKD. The clinical characteristics are reported in Figure 1 . Our DNAJB11-PKD cohort vs ADPKD presented significantly a normal renal size (median value 10.5cm vs 16cm respectively) and smaller cysts size (median value 2cm vs 5cm respectively). Interestingly 5/19 DNAJB11 patients had type 2 diabetes vs no cases in the ADPKD group (p&lt;0.05). ADPKD patients presented ESRD about 10 years before DNAJB11-PKD and renal survival resulted significantly worse (Figure 2).We revised also the previous diagnosis of our DNAJB11-PKD patients; 3/19 DNAJB11-PKD cases were diagnosed as having ADPKD. The remaining were classified as medullary sponge kidney disease (7/19), diabetic nephropathy (3/19) or nephroangiosclerosis (6/19).

Conclusion
DNAJB11 mutations were reported as a cause of ADPKD for the first time in May 2018 by Cornec-Le-Gall and colleagues. In their study were reported 7 different mutations in 23 patients and they identified 2/23 patients with type II diabetes. We here report the larger single DNAJB11 mutation cohort in the literature and compared it with genetic proven ADPKD. We documented differences in pathognomonic clinical features of ADPKD like renal survival, enlarged kidneys and bulky cysts. Moreover about 30% of DNAJB11-PKD patients present Type II diabetes that would be related to altered proteostasis in the ER. Since DNAJB11-PKD appears to differ in relevant aspects from well known ADPKD, it would be less confusing to classify DNAJB11-PKD indipendently from ADPKD.