Authors :
Presenting Author: Francesca Bisulli, MD, PhD – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy
Lorenzo Ferri, MD – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy; Ester Cifaldi, mrs – Medical Genetics Unit, Polyclinic Sant'Orsola-Malpighi University Hospital, Bologna, Italy; Laura Licchetta, Md,PhD – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy; Raffaella Minardi, PhD – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy; Barbara Mostacci, Md,PhD – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy; Paola Dimartino, PhD – Medical Genetics Unit, Polyclinic Sant'Orsola-Malpighi University Hospital, Bologna, Italy; Elena Pasini, MD – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy; Laura Rossini, PhD – Clinical Epileptology and Experimental Neurophysiology Unit IRCCS Foundation, Neurological Institute “C.Besta”, Milan, Italy; Michele Rizzi, MD – Clinical Epileptology and Experimental Neurophysiology Unit IRCCS Foundation, Neurological Institute “C.Besta”, Milan, Italy; Alessia Percivalle, mrs – Medical Genetics Unit, Polyclinic Sant'Orsola-Malpighi University Hospital, Bologna, Italy; Gianluca Marucci, PhD – Neuropathology Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy.; Matteo Martinoni, MD – Department of Medical and Surgical Sciences, University of Bologna, Bologna, Italy; Chiara Pastori, MD – Clinical Epileptology and Experimental Neurophysiology Unit IRCCS Foundation, Neurological Institute “C.Besta”, Milan, Italy; Marco Seri, PhD – Department of Biomedical and NeuroMotor Sciences (DIBINEM), University of Bologna, Italy – Medical Genetics Unit, Polyclinic Sant'Orsola-Malpighi University Hospital, Bologna, Italy; Roberto Michelucci, MD – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy; Marco De Curtis, MD, PhD – Clinical Epileptology and Experimental Neurophysiology Unit IRCCS Foundation, Neurological Institute “C.Besta”, Milan, Italy.; Leonardo Caporali, PhD – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy; Rita Garbelli, PhD – Clinical Epileptology and Experimental Neurophysiology Unit IRCCS Foundation, Neurological Institute “C.Besta”, Milan, Italy.; Tommaso Pippucci, PhD – Department of Biomedical and NeuroMotor Sciences (DIBINEM), University of Bologna, Italy – Medical Genetics Unit, Polyclinic Sant'Orsola-Malpighi University Hospital, Bologna, Italy; Laura Tassi, MD – Claudio Munari Epilepsy Surgery Center, Niguarda Hospital, Milan, Italy; Francesca Bisulli, MD, PhD – Department of Biomedical and NeuroMotor Sciences (DIBINEM), University of Bologna, Italy – IRCCS Istituto delle Scienze Neurologiche di Bologna, Epilepsy Center (full member of the European Reference Network EpiCARE), Bologna, Italy
Rationale:
Epileptogenic lesions, such as focal cortical dysplasia (FCD) and low-grade epilepsy-associated neuroepithelial tumors (LEAT), are two of the main cause of drug-resistant structural epilepsy.
1 Recent studies have disclosed a growing number of pathogenic somatic and germline variants responsible for these lesions especially in genes encoding components of PI3K-AKT-mTOR and RAS-MAPK pathway, respectively.
2 However, the exact prevalence of pathogenic variants and their role in surgical outcome have still to be clarified.
Methods:
Consecutive patients who underwent epilepsy surgery at Claudio Munari Epilepsy Surgery Center and at IRCCS Istituto delle Scienze Neurologiche between 2018-2021 were included in the study. For each patient the DNA obtained from Fresh Frozen (FF) brain specimen resected during surgery and matched peripheral blood were analyzed. Retrospective formalin-fixed paraffin-embedded (FFPE) brain tissues obtained from the Clinical Epileptology and Experimental Neurophysiology Unit IRCCS, Neurological Institute “C. Besta” were also analyzed. We designed 2 target panels of genes associated to FCD and LEAT using single molecule Molecular Inversion Probes (smMIPs). The FCD panel comprised 14 genes (AKT1, AKT3, CASK, DEPDC5, MTOR, NPRL2, NPRL3, PIK3CA, PTEN, RHEB, SLC35A2, TSC1, TSC2, KRAS) while LEAT panel includes 10 genes (TRX, BRAF, FGFR1, GFAP, IDH1, KRAS, NF1, PDGFRA, RB1, TEK, TP53, PTEN).
Results:
A total of 164 pediatric and adults patients were included (72F, mean age 30,6 range 6-65). FF brain specimen was available for 143, FFPE for 21. Based on histopathological analysis patients were classified in 4 group: FCD 60 patients, LEAT 28, Scars 10, other-lesion or not-lesional 66. We performed preliminary genetic analysis on 127 brain and blood specimens (30 FCD, 28 LEAT patients and 10 Scars). We identified 11 pathogenic variants in FCD group (36%): 2 germline in TSC1 and 9 somatic (7 in MTOR with Variant Allele Frequency (VAF) 1-3%, 1 in RHEB (VAF: 2%) and 1 in SLC35A2 (VAF: 2,49%). Ten patients in LEAT group showed pathogenic somatic variant in BRAF (VAF 2-9%) and 1 in IDH1 (VAF 25%). None of the patients in scar group had positive results for both panels.
Conclusions:
We confirm that mTOR and BRAF mutations account for the majority of FCDII and LEAT cases, further contributing to recognize a genetic basis of these epileptogenic lesions. Somatic mutations of SLC35A2 are increasingly detected in FCDI-related epilepsy. Our study reports the optimal diagnostic accuracy of smMIP in the identification of somatic variants with low VAF in FCDI, FCDII, and LEAT patients who underwent epilepsy surgery.
1 Hoffmann L, Blümcke I. Neuropathology and epilepsy surgery. Curr Opin Neurol. 2022. doi: 10.1097/WCO.0000000000001030.
2 López-Rivera JA et al. The genomic landscape across 474 surgically accessible epileptogenic human brain lesions. Brain. 2023. doi: 10.1093/brain/awac376.
Funding: The study was supported by the Italian Ministry of Health (RF-2019-12370564 to Francesca Bisulli)