title: LGI2 truncation causes a remitting focal epilepsy in dogs.
abstract: One quadrillion synapses are laid in the first two years of postnatal construction of the human brain, which are then pruned until age 10 to 500 trillion synapses composing the final network. Genetic epilepsies are the most common neurological diseases with onset during pruning, affecting 0.5% of 2-10-year-old children, and these epilepsies are often characterized by spontaneous remission. We previously described a remitting epilepsy in the Lagotto romagnolo canine breed. Here, we identify the gene defect and affected neurochemical pathway. We reconstructed a large Lagotto pedigree of around 34 affected animals. Using genome-wide association in 11 discordant sib-pairs from this pedigree, we mapped the disease locus to a 1.7 Mb region of homozygosity in chromosome 3 where we identified a protein-truncating mutation in the Lgi2 gene, a homologue of the human epilepsy gene LGI1. We show that LGI2, like LGI1, is neuronally secreted and acts on metalloproteinase-lacking members of the ADAM family of neuronal receptors, which function in synapse remodeling, and that LGI2 truncation, like LGI1 truncations, prevents secretion and ADAM interaction. The resulting epilepsy onsets at around seven weeks (equivalent to human two years), and remits by four months (human eight years), versus onset after age eight in the majority of human patients with LGI1 mutations. Finally, we show that Lgi2 is expressed highly in the immediate post-natal period until halfway through pruning, unlike Lgi1, which is expressed in the latter part of pruning and beyond. LGI2 acts at least in part through the same ADAM receptors as LGI1, but earlier, ensuring electrical stability (absence of epilepsy) during pruning years, preceding this same function performed by LGI1 in later years. LGI2 should be considered a candidate gene for common remitting childhood epilepsies, and LGI2-to-LGI1 transition for mechanisms of childhood epilepsy remission.
authors.affiliation: Department of Veterinary Biosciences, Department of Medical Genetics, Research Programs Unit, Molecular Medicine, University of Helsinki, Helsinki, Finland.
authors.forename: Eija H
authors.initials: EH
authors.lastname: Seppälä
authors.forename: Tarja S
authors.initials: TS
authors.lastname: Jokinen
authors.forename: Masaki
authors.initials: M
authors.lastname: Fukata
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fukata
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Webster
authors.forename: Elinor K
authors.initials: EK
authors.lastname: Karlsson
authors.forename: Sami K
authors.initials: SK
authors.lastname: Kilpinen
authors.forename: Frank
authors.initials: F
authors.lastname: Steffen
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Dietschi
authors.forename: Tosso
authors.initials: T
authors.lastname: Leeb
authors.forename: Ranja
authors.initials: R
authors.lastname: Eklund
authors.forename: Xiaochu
authors.initials: X
authors.lastname: Zhao
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Rilstone
authors.forename: Kerstin
authors.initials: K
authors.lastname: Lindblad-Toh
authors.forename: Berge A
authors.initials: BA
authors.lastname: Minassian
authors.forename: Hannes
authors.initials: H
authors.lastname: Lohi
mesh_terms: D051722:ADAM Proteins / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D019556:COS Cells; D002522:Chlorocebus aethiops; D004285:Dogs; D004828:Epilepsies, Partial / Q000235:genetics* / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D055106:Genome-Wide Association Study; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011485:Protein Binding / Q000502:physiology; D051381:Rats
chemical_list: D009419:Nerve Tissue Proteins; D051722:ADAM Proteins