Idiopathic Generalized Epilepsy (IGE) is one of the most common forms of epilepsy, representing about 30% of all epilepsies;and, its etiology is considered to be mostly genetic. Both linkage and association studies have identified several candidate genes for IGE, namely: malic enzyme 2 (ME2) and bromodomain containing 2 (BRD2). In addition, previous studies have also suggested that IGE susceptibility results from gene-gene interaction. We will focus on establishing a clear biological link between ME2 and IGE, and we will also test for an interaction between ME2 and BRD2. The strong linkage and association results on chromosome 18 suggest that ME2 is a general IGE susceptibility locus, and that it follows a recessive mode of inheritance. Sequence analysis in 20 IGE cases and 18 controls, revealed a region in intron 1 of ME2 where polymorphic sites in cases are mostly monomorphic in controls. Moreover, ME2 is an excellent biological candidate for susceptibility to IGE due to: 1) its abundance in brain neurons;2) its localization to the mitochondria;and most compelling, 3) its catalytic function of malate decarboxylation, producing a critical supply of pyruvate for glutamate and GABA synthesis. GABA is the main inhibitory neurotransmitter in the central nervous system, and is involved in the modulation of epileptiform spike-wave activity. Anti-epilepsy drug mechanisms also modulate the GABA neurotransmitter system, and mutations in GABA receptors have been shown to play a role in susceptibility to some forms of epilepsy. In this grant application, we will determine the different haplotypes of ME2 intron 1 based on our selected sample of cases for whom sequence data is available. Then, we will use reporter constructs to examine the isolated effects of different intron 1 haplotypes on splicing and levels of transcription. Note that our reporter constructs will only contain proximal promoter elements and intron 1. Next, we will examine the effects of intron 1 variants in neuronal and/or glial cells;and unlike our reporter constructs, these experiments will involve the entire ME2 gene. Finally, using standard resampling methods and a novel statistical approach, we will test for an interaction between ME2 and BRD2 with respect to juvenile myclonic epilepsy-an IGE subtype. Overall, this propose research should help to elucidate the general role of ME2 as a susceptibility gene for IGE, as well as its particular role in a network of other contributing genetic factors.
Epilepsy affects 2.7 million people in the US alone. Idiopathic Generalized Epilepsy (IGE) accounts for 30% of all epilepsy, starts in childhood or adolescence, and, is thought to have a genetic etiology. Our studies have identified a gene (ME2) as both linked and strongly associated with several different, common IGE syndromes, including Juvenile Myoclonic Epilepsy (JME), Juvenile Absence Epilepsy (JAE), and Epilepsy with Generalized Tonic-Clonic Seizures (EGTCS). We propose to determine how polymorphisms found in the ME2 gene increase susceptibility to a broad class of related epilepsy syndromes.
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