Epilepsy is one of the most common and serious neurological disorders, with up to 60 million people affected worldwide.¹ Juvenile myoclonic epilepsy (JME) is a common familial form that accounts for 5–10% of all epilepsy cases.² This form belongs to the idiopathic epilepsy group, due to the absence of detectable structural or metabolic abnormalities. Clinically, JME is mainly characterised by isolated myoclonic jerks on awakening that usually begin during adolescence. It is also highly drug-dependent, since a 90% recurrence is reported after interruption of pharmacological treatment.³

Studies on the incidence of epilepsy in relatives of probands with JME, as well as on twins, have provided strong evidence for a genetic contribution.^4,5 Autosomal dominant, autosomal recessive, two locus, monogenic, and polygenic models of inheritance have been suggested.⁶ So far, three genes that are mutated in different forms of JME have been identified, namely CACNB4,⁷GABRA1,⁸ and CLCN2.⁹ In addition, two different susceptibility loci have been identified by linkage analysis. The first locus, termed EJM1 (OMIM 254770), is on the human leukocyte antigen region of chromosome 6p.¹⁰ Although no trait-causing mutation has yet been identified at this locus, association with a haplotype of the BRD2 gene has been recently reported.¹¹ The second locus, termed EJM2 (OMIM 604827), is in the region of chromosome 15q that contains the gene coding for the α7-nicotinic acetylcholine receptor subunit. Genetic mapping of the EJM2 locus defined a 15.1 cM candidate region on chromosome 15q14, flanked by the D15S165 and D15S971 loci.⁶ Interestingly, this region includes the CX36 gene, which codes for the first connexin identified in neurons.¹²

Connexins are integral membrane proteins, encoded by a family of at least 20 genes in humans, which form the subunits of gap junction …