Abstracts

Rationale: In humans, the linkage and association of BRD2 gene to juvenile myoclonic epilepsy (JME) has been replicated by multiple studies. In mice, the Brd2 null mutation (Brd2-/-) is embryonic lethal at mid-gestation and the embryos exhibit abnormal neural development. The heterozygous Brd2 /- mice are viable, enabling us to study both seizure susceptibility and look for anatomical changes in underlying brain structures that, in comparison with / controls, could explain an effect on seizures. The anatomical changes were investigated in the structures involved in control of generalized seizures, i.e., in the basal ganglia network. Methods: The Brd2 knock out mice were created using a gene-trap approach (Shang et al, Dev Dyn 238:908-17; 2009). Seizure susceptibility was tested using flurothyl. Spontaneous seizures were recorded with EEG/videomonitoring setup with infrared capability. GABAergic markers (parvalbumin and GAD67) were detected using immunostaining. Relative numbers of immunopositive cells were compared between /- and / mice and densitometry was used to compare immunoexpression of staining in the primary motor cortex, striatum/globus pallidus, the substantia nigra, and the superior colicullus. Results: Seizure susceptibility was changed in sex-specific fashion: Male Brd2 /- had decreased threshold for clonic seizures, while female Brd2 /- mice for tonic-clonic seizures compared to / mice of the respective sex. We performed long-term EEG/videorecordings in five Brd2 /- mice. In the three mice (out of five observed to date), spontaneous clonic seizures were recorded ranging in duration from several seconds to tens of minutes. One mouse died while in status epilepticus. Immunohistochemistry and cell number comparisons demonstrated significant downregulation of GABA markers irrespective of sex in the primary motor cortex, substantia nigra reticulata, and superior collicullus, but not in the hippocampus in Brd2 /- mice in comparison with / controls. Conclusions: Our study is the first to demonstrate a non-channel JME gene associated with downregulation of GABA markers, increases in seizure susceptibility and occurrence of spontaneous seizures. These findings strengthen the hypothesis that mutations in human BRD2 gene contribute to the occurrence of JME. The impairment of the GABAergic system suggests that a mechanism for IGE may be a deficit of GABAergic neurons.