Abstracts

Rationale: Juvenile myoclonic epilepsy (JME) is a common genetic generalized epilepsy, representing 3-12% of all epilepsies. JME typically starts between 12 and 18 years of age with myoclonus occurring early in the morning. Most patients have tonic-clonic seizures and many also have absence seizures. JME patients usually have electroencephalographic (EEG) 3.5 to 6.0 Hz diffuse polyspike-wave complexes. JME can be inherited as a Mendelian autosomal dominant or autosomal recessive trait or as a non-Mendelian complex genetic trait. Linkage studies have demonstrated at least 22 chromosome loci for JME. Three mutation-harboring Mendelian genes for JME, CACNB4 (Escayg A et al., 2000; MIM 601949), GABRA1 (Cossette P., et al 2002; MIM 137160) and EFHC1 (Suzuki, et al., 2004; MIM 608815) have been reported. In this study, we identified a novel mutation of K305T in myclonin 3 in a four-generation family with classic JME. K305T in myclonin 3 segregates with all eight affected members.Methods: We studied a four generation European/Amerinds family with classic JME and 232 population controls. Thirty-seven family members (eight affected and 29 unaffected) participated in this study. Among eight affected members, four had classical JME and another four did not have clinical symptoms, but had EEG polyspike wave complexes. Linkage analysis using Marshfield genome wide scan set 16, a standard 10 cM scan with 400 STRP's and fine mapping of 6p11-12 locus with 38 additional microsatellite markers were performed. A pair-end whole exome sequence on six samples including four affected members and two married-in controls was performed by fasttrack genetic analysis service of Illumina on a HiSeq 2000 sequencing system. ANNOVAR program (Wang K et al., 2010) was used to annotate, filter and prioritize the functional DNA variants. Mendelian inheritance segregation of candidate variants in 8 affected members and Sanger sequencing of all 37 family members were confirmed the identified DNA variant. Results: Two point parametric genome-wide linkage scan suggested linkage to D6S1053 with a LOD score of 2.30 at theta=0.05 and to D6S1017 with a LOD score of 2.28 at theta=0.00. Fine mapping on chromosome 6p confirmed linkage to 6p12, e.g. D6S257 with LOD score of 3.35 and D6S1573 with LOD score of 3.27, both at theta=0.00. Whole exome sequencing identified a heterozygous mutation of A914C/K305T in myclonin 3, which located perfectly in chromosome 6p12.2 identified by genome-wide linkage scan and 6p fine mapping. Heterozygous mutation of A914C /K305T in myclonin 3 segregates with eight clinically and EEG polyspike wave affected members and four carriers in the four generation family with classic JME and not in 232 population controls. Conclusions: Our data strongly suggest myclonin 3 is a novel gene that causes juvenile myoclonic epilepsy.