#6681 MT-TL1 M.3243A>G MITOCHONDRIAL DNA VARIANT DETECTED FROM WHOLE EXOME SEQUENCING CAN EXPLAIN CASES OF ADULT UNKNOWN NEPHROPATHIES

Abstract

Abstract Background and Aims In a population-based study, mainly constituted of unknown nephropathies (cohort Sorbonne University, Paris, France N = 1197 patients), beyond reporting the diagnostic yield of nuclear genes, we also investigated the incidence of the mtDNA pathogenic variant MT-TL1 m.3243A>G. This variation was systematically searched from whole exome sequencing (WES) data. In retrospect, we described the renal phenotype and studied the heteroplasmy level of the mtDNA variation in urine or kidney tissues compared to its blood fraction. The prevalence of m.3243A>G has been estimated ranging from 0.08% to up to 0.25%. Method From September 2018, to February 2023, WES has been prospectively performed, as a first exploration of adult's nephropathies of unknown origin or when a genetic renal disease was clinically suggested. As off-target result, we retrieved m.3243A>G variation in blood DNA and then determined the mtDNA heteroplasmic level respective from urine sample or kidney tissue when available with an orthogonal method. Results We report a molecular diagnosis in 294 over 1197 adult patients sequenced (diagnostic yield: 24%, Age 43 y/o in average). Among these 294 patients with molecular diagnoses, 48 were distinct monogenic disorders, out of which 8 accounted for 52% of the genetic diagnoses. MT-TL1 m.3243A>G pathogenic variant was detected in 1,7% of the patients (20 patients over 1197 patients). An orthogonal method confirmed the presence of m.3243A>G variant in 10 patients supporting the possibility to diagnose from blood DNA analysed by WES. In all cases, the presence of m.3243A>G had major clinical implications for the patients and their families: living related donor aborted for two patients, a molecular diagnosis in three patients with unknown nephropathies and in three patients with histological diagnosis of focal segmental glomerulosclerosis. Other mitochondrial diseases appeared less likely involved in our adult cohort (only one patient with COQ2 pathogenic variants). Conclusion This population-based study reinforces the place of WES as first-tier exploration for adult patients with chronic kidney disease in whom phenotypes are often poor and/or atypical. The mitochondrial genome analysis with the same assay allowed the detection of yet unsuspected MT-TL1 m.3243A>G variant in 1,7% of patients suggesting enrichment compared to current prevalence observed in other population. Our data suggest that the entity “mitochondrial nephropathy” can represent a significant part of adult unknown nephropathies.