Galanin mutations in temporal lobe epilepsy. M. Guipponi1, A. Chentouf2, K. E. B. Webling3, K. Freimann3, A. Crespel4, C. Nobile5, T. Dorn6, J. Hansen6, J. Lemke7,8, G. Lesca9,10,11, F. Becker12, U. Stephani13, H. Muhle13, I. Helbig13, P. Ryvlin14, E. Hirsch15, G. Rudolf15, C. Gehrig1, F. Santoni1, M. Pizzato16, U. Langel3, S. E. Antonarakis1,17 1) Genetic Medecine, University of Geneva Medical School, Geneva, Switzerland; 2) Service of Neurology, CHU Oran, Oran, Algeria; 3) Department of Neurochemistry, Arrhenius Laboratories for Natural Science, Stockholm University, Stockholm, Sweden; 4) Departement of Neurology, Montpellier University Hospital, France; 5) Institute of Neurosciences, Section of Padua, Padova, Italy; 6) Swiss epilepsy center, Zürich, Switzerland; 7) Division of Human Genetics, University Childrens Hospital Inselspital, Bern, Switzerland; 8) Institute of Human Genetics, University Hospital Leipzig, Germany; 9) Department of Medical Genetics, Hospices Civils de Lyon, France; 10) Claude Bernard Lyon I University, Lyon, France; CRNL, CNRS UMR 5292; 11) CRNL, CNRS UMR 5292; INSERM U1028, Lyon, France; 12) Department of Neurology and Epileptology, University of Tübingen, 72076 Tübingen, Germany; 13) Department of Neuropediatrics, University Medical Center Schleswig-Holstein (UKSH), Kiel, Germany; 14) Service of Neurology and Epileptology, CHU lyon-GH Est, Lyon, France; 15) Department of Neurology, INSERM UMR 7191, CHU Strasbourg-Hôpital Civil, Strasbourg, France; 16) Centre for integrative Biology (CIBIO), University of Trenton, Trenton, Italy; 17) Institute of Genetics and Genomics in Geneva (iGE3), Geneva, Switzerland.
Temporal lobe epilepsy (TLE) is a common and heterogeneous epilepsy syndrome with a complex etiology. Despite strong evidence for the participation of genetic factors, the genetic basis of TLE remains largely unknown. Here, we studied a family with a pair of monozygotic twins affected by temporal lobe epilepsy and two unaffected siblings born to healthy parents. Exome sequencing revealed that the twins carried a de novo missense mutation (A39E) in the galanin/GMAP prepropeptide (GAL) gene. In an independent cohort of 591 unrelated TLE patients, we observed 2 cases carrying heterozygous missense mutations in the GAL gene. One patient had the same mutation (A39E) as found in the monozygotic twins and the other carried an E65K substitution. Both mutations were predicted as damaging and were absent from dbSNPv138, 1000Genomes and EVS databases. Galanin is a 30-amino acid neuropeptide produced from the cleavage of the 123-amino acid preprogalanin protein, which acts as a potent anticonvulsivant and regulates epileptic seizures in animal models. The A39E mutation is located within the 5-half of galanin which is highly conserved and critical for binding to receptors (GalR) and biological activity. Consistently, competitive binding assays showed that the A39E mutant had a significantly reduced binding affinity for GalR2 and GalR3 but not for GalR1 when compared to that of wild type galanin. The E65K mutant is located just downstream of the 3 dibasic tryptic cleavage site of the galanin neuropeptide. Using western blot analysis, we obtained preliminary data suggesting that the E65K mutation impaired galanin cleavage and would lead to the generation of a 3uncleaved peptide with potentially altered binding and/or signaling activities. Over the last decade, galanin has emerged as a potent inhibitor of epileptic activity in animal models. Here, we report the identification of mutations interfering with galanin activity in individuals with temporal lobe epilepsy. Given the availability of galanin agonists, our findings could potentially have direct implication for the treatment of individuals with TLE.