1. The study was supported by EuroEPINOMICS grant SARLA 11091E RESULTS BACKGROUND COPY NUMBER VARIANTS ASSOCIATED WITH DRUG-RESISTANT EPILEPSY IN ESTONIA K. Noormets 1, I. Talvik 1, T. Reimand 2, E. Õiglane-Šlik 1, K. Õunap 2, T. Talvik 1 1 Children’s Clinic of Tartu University Hospital, 2 United Laboratories of Tartu University Clinic, Department of Genetics, Tartu, ESTONIA Epilepsy is one of the most common neurological disorders in humans with a prevalence of 1% and a lifetime incidence of 3%. Approximately 20%–30% of children develop refractory epilepsy (1). Drug resistant epilepsy may be defined as failure of adequate trials of two tolerated and appropriately chosen and used AED schedules (whether as monotherapies or in combination) to achieve sustained seizure freedom (2). Drug-resistant epilepsy is a serious problem for the families and physicians. The copy number variants (CNVs) are known to play an important role in the genetic etiology of many neurodevelopmental disorders, including intellectual disability, autism, and schizophrenia (3). Still the role of many copy number variants (CNV) is unknown. Microarray-based genomic copy-number analysis (chromosomal microarray – CMA) gives us a chance to detect very small chromosomal imbalances associated with different diseases. Today, the “molecular karyotype” is rapidly replacing the conventional karyotype in diagnostic and research laboratories. Molecular karyotyping refers to the evaluation of chromosome content and structure using DNA hybridization rather than direct observation of chromosomes under the microscope. Advances in technology over the past several years now allow clinicians and researchers to interrogate the entire genome for CNVs (deletions and duplications) in one experiment (2). PATIENTS AND METHODS AIM REFERENCES 1p36 deletion CONCLUSIONS To find out if patients with drug-resistant epilepsy in Estonia carry different CMV’s and to determine the relevance of these mutations according to epilepsy. Estonian database of CMA analyses consists data of 1100 patients, analyzed since 2009. 165 of them are children with epilepsy aged 0-18 years. From these 165 children 78 (47,3%) meet the criteria of ILAE definition of drug-resistant epilepsy. CMA changes on were found in 46/165 (27,9%) of children with epilepsy In the study group of 78 children with drug resistant epilepsy CMA changes were found in 31 (39.7%) In the group of 31 children with drug resistant epilepsy we detected loss of heterozygosity (LOH) in 8 (25.8%), duplications in 10 (32.3%) and deletions in 13 (41.9%) cases. In 7/8 patients with LOH the association with epilepsy is not clear (Xp13.2-q21.1, 11q11-q14.1, 13q14, 2p12-p13.3, 11p11.2-p11.12, 7q32.3-q34 and 11p11.2-p11.12). In one case 3q13.13-q21.1 LOH is associated with epilepsy as in this region the CASR (calcium sensing receptor) gene is located, causing hypocalciuric hypercalcemia, pancreatitis and idiopathic epilepsy syndrome. Our patient has only idiopathic focal epilepsy since the age of 4 years, and cognitive decline. In 10 cases we found duplication: In 4 cases the association with the phenotype is not known: 2p22.3, 5q35.3 and 22q11.21 (in one patient), 11p11.12 and 12q24.32 duplication. 3p11.1 - A boy with focal epilepsy since the age of 3 years and Tourette syndrome. No dysmorphic features. Normal cognitive development 46,XY, inv dup del(8)(p11→p23::p23→p11::p11→qter)dn – A boy with focal epilepsy since the age of 2 months: eye fixation. Global developmental delay. 15q11.2-13.1 – The girl has developmental delay, slight dysmorphic features: mongoloid-shaped eyes, short philtrum and focal epilepsy since the age of 4 years. Family and perinatal history is uneventful. 17p11.2 - Potocki-Lupski syndrome. The girl was born in term, in asphyxia with Apgar score 0/3/6. Had therapeutic cooling and neurosurgical intervention at the age of 72 hours due to subdural hemorrhage. Seizures since the age of 1 year complex partial epilepsy, developmental delay. No dysmorphic features. 17p13.3 – The patient has focal epilepsy, no patients with epilepsy has been described before. 22q13.1 - The boy has epilepsy since 6 years of age: absence like seizures with generalized epileptic discharges. The child has mild intellectual disability (ID). In 13 patients deletions were deteted. 1p36 deletion syndrome -The girl had seizures since the age of 2 months (infantile spasms). Global developmental delay. 8p23.3 –p23.1 deletion (2 patients) - The girl has ID and has focal seizures since the age of 5 years. The boy has dysmorhic features and focal seizures since the age of 2 months 8p23.2 deletion - The boy has autistic spectrum disorder and focal epilepsy. 8q24.13-q24.21 deletion - The child has developmental delay and focal epilepsy. 11q23.3 deletion - The girl has focal epilepsy since the age of 3 years, at the age of 16 years she has personality issues, sleeping disturbances. 13q33.1-q34 deletion - Our patient has global developmental delay and focal epilepsy. 15q11.-1q14 deletion – Prader-Willi syndrome - The child has complex focal epilepsy and global developmental delay with profound hypotonia. 16p11.2 deletion syndrome – boy with slow development and focal epilepsy, no dysmorphic features. 16p12.2 deletion- girl with slow development and focal seizures. 22q13.2 deletion - The child has focal epilepsy but normal development. 22q13.31-q13.33 deletion or telomeric 22q13 monosomy syndrome or Phelan-McDermid syndrome – A girl with epilepsy with complex partial seizures. At the age of 8 years she has ID, no speech but she is seizure free. 45,X,del(X)(p11) - The child has global developmental delay and focal epilepsy since the age of 1.6 years. She has OTC deficiency. In addition we have diagnosed: Ring chromosome 20 – a girl with partial seizures and ID 47XXX – a girl with generalized epilepsy and slight learning disabilty 48XXXX – a girl with focal epilepsy and global developmental delay CMA is an useful diagnostic tool in detection of CNV's in drugresistant epilepsy. Almost half of the analyzed patients had CNV’s but further identification of variant loci and the genes within them warrant further evaluation. 1.Sillanpää M, Schmidt D. Natural history of treated childhood-onset epilepsy: prospective, long-term population-based study. Brain. 2006 Mar;129(Pt 3):617-24. 2.Kwan et al. Definition of drug resistant epilepsy: Consensus proposal by the ad hoc Task Force of the ILAE Commission on Therapeutic Strategies. Epilepsia. 2010 51(6): 1069-1077. 3.Mefford et al. Genome-wide Copy Number Variation in Epilepsy: Novel Succeptibility Loci in Idiopathic Generalized and Focal Epilepsies. PLoS Genet. 2010 May; 6(5)