Abstracts

Rationale: Idiopathic focal epilepsies comprise various epilepsy syndromes characterized by the unifying EEG trait of centrotemporal spikes (CTS). Deletions of the chromosomal region 16p13.2 including GRIN2A were previously identified in three patients with complex phenotypes of focal epilepsies with CTS, dysmorphic features and various degrees of intellectual disability (Reutlinger et al., Epilepsia, in press). GRIN2A, coding for the alpha 2 subunit of the glutamatergic NMDA receptor is involved in the modulation of synaptic activity, representing a prime candidate gene for epileptogenesis. Methods: Mutation analysis of GRIN2A including all exons, exon-intron boundaries and the promoter region was performed in a cohort of 44 patients with CTS (Benign Rolandic Epilepsy n=35, Atypical Benign Partial Epilepsy n=9) using the NCBI Primer Set RSS000057426.1 and additionally designed primers. NovoSNP was used for the evaluation of single nucleotid polymorphisms (SNPs) and indels. Pathogenic implications of identified coding variants were assessed by four different in-silico analysis programs (PolyPhen, SIFT, SNAP, Panther). For intronic SNPs, splice site analysis was performed using NetGene 2, Splice View and HSF2.4. Results: In total, 26 single nucleotide polymorphisms were identified, including 5 previously unknown non-coding variants and 3 missense mutations resulting in amino acid exchange. A possibly pathogenic mutation (c.728C>T, p.Ala43Val) was identified in a patient with Benign Rolandic Epilepsy, behavioural problems and learning disability, which was not observed in 384 population controls. Conclusions: Mutation analysis of GRIN2A in patients with CTS and epilepsy syndromes of the Rolandic spectrum identified one missense mutation localized in the ligand-binding domain of the alpha-2 NMDA receptor subunit. This further supports earlier findings suggesting the involvement of altered glutamatergic transmission in the generation of centrotemporal spikes. Further studies including larger patient cohorts and functional analysis of the mutant protein are needed to validate these findings.