Authors :
Presenting Author: Samuel Gooley, MD – Melbourne University
Piero Perucca, MD, PhD – Melbourne University
Emma Macdonald-Laurs, MBChB – Royal Children’s Hospital Melbourne:
Tom Witkowski, BSc (Hons) – Epilepsy Research Centre, Department of Medicine, University of Melbourne, Austin Health, Melbourne, Victoria, Australia
Karl Martin Klein, MD, PhD – Foothills Medical Centre, Canada
Joshua Reid, Msc – Melbourne University
Sian Macdonald, MSc – Epilepsy Research Centre, Department of Medicine, University of Melbourne, Austin Health, Melbourne, Victoria, Australia
Marian Todaro, PhD – Alfred Health, Australia
Paul Lockhart, PhD – Royal Children's Hospital and Murdoch Children's Research Institute, Australia
Simon Harvey, MBBS, PhD – Royal Children's Hospital, Australia
Silvia Cases, PhD – Bonn University
Albert Becker, MD, PhD – Bonn University
Richard Leventer, MD, PhD – Royal Children's Hospital, Australia
Sarah Stephenson, PhD – Murdoch Children's Research Institute, Australia
Jonathan Clark, MD – Austin Health, Australia
Kristian Bulluss, MD – Austin Health, Australia
Marco De Curtis, MD – Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
Rita Garbelli, – IRCCS Foundation Neurological Institute Carlo Besta
Laura Tassi, MD – Niguarda Hospital, Milan, Italy
Mark Cook, MD, PhD – St Vincent's Health, Australia
Terrence J. O'Brien, MB, BS, MD, FRACP, FRCPE, FAHMS, FAES – Monash University, Melbourne, VIC, Australia
Ingrid Scheffer, MBBS, PhD, FRACP, FRS – University of Melbourne, Austin Health; The Florey Institute of Neuroscience and Mental Health, University of Melbourne; University of Melbourne, Royal Children’s Hospital; Murdoch Children’s Research Institute
Samuel Berkovic, MD – Epilepsy Research Centre, Department of Medicine, University of Melbourne, Austin Health, Melbourne, Victoria, Australia
Michael Hildebrand, PhD – Epilepsy Research Centre, Department of Medicine, University of Melbourne, Austin Health, Melbourne, Victoria, Australia; Neuroscience Group, Murdoch Children’s Research Institute, Parkville, Victoria, Australia
Rationale:
Antecedent events such as prolonged febrile seizures, encephalitis, and traumatic brain injuries are established risk factors for mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE+HS). This led to MTLE+HS being conceptualised as a largely acquired condition. However, emerging evidence suggests that somatic variants in the Ras/Raf/MAPK (Ras) pathway may contribute with a recent study suggesting ~10% of MTLE+HS patients harbour activating somatic Ras pathway variants in their resected hippocampal tissue.
Here, we expand on these findings by validating the presence of somatic Ras pathway variants in an independent MTLE+HS cohort and reveal novel genetic contributions from other oncogenes.
Methods:
We collected fresh frozen resected hippocampal tissue from a retrospective cohort (n=106) of MTLE+HS patients. This new series includes cases from Australia, Canada, Germany and Italy, and controls (n=30) without epilepsy. Clinical data was analysed and high-depth duplex sequencing using a custom designed gene panel targeting 36 Ras genes and 104 other cancer and epilepsy genes was performed on hippocampal tissue from all cases and controls.
Results:
To date, DNA from 46 hippocampal specimens (n=32 cases and 14 controls) has been sequenced. At least one pathogenic somatic variant was detected in 6/32 cases (18%) and 0/14 controls (p= 0.097).
Two or more pathogenic somatic NF1 variants were detected in the hippocampal tissue of three individuals with MTLE+HS and other lesions (Table 1), with a variant allele fraction (VAF) ranging from 0.28–19.8%. A somatic TSC2 (p.Gln1503*) variant (VAF 0.83%) was detected in a case with a form fruste of tuberous sclerosis and previously negative genetic testing. A somatic KMT2D (p.Arg5086*) variant (VAF 18%) was found in an individual with late-onset non-lesional MTLE+HS. KMT2D has not previously been associated with MTLE+HS and is not a canonical Ras gene, but loss-of-function somatic KMT2D variants are known to activate Ras signalling in tumours.
Conclusions:
With a ‘hit rate’ of 18% of MTLE+HS cases to date, we expect to find somatic variants in at least 20 individuals once our entire cohort is sequenced, including novel disease associations such as mosaicism for KMT2D in MTLE+HS. Correlating these genetic findings with detailed phenotyping will allow us to explore the interplay between acquired and genetic factors, potentially enabling us to reconceptualise MTLE+HS as a disease with contributions from both.
Funding:
National Health and Medical Research Council Australia, Austin Medical Research Foundation and Bonn-University of Melbourne Research Excellence Fund.