Abstracts

Rationale: Generalized epilepsy with febrile seizures plus (GEFS+) is an autosomal dominant epilepsy syndrome characterized by classic febrile seizures (FS) or febrile seizures plus (FS+) (defined as febrile seizures that persist beyond age 6 or are accompanied by afebrile generalized tonic-clonic seizures). Mutations in four genes have been identified in GEFS+ families, but they account for only a small proportion of GEFS+. Here we report a novel region of genetic linkage on chromosome 6q in a newly identified pedigree with GEFS+. Methods: The pedigree was recruited in the Epilepsy Family Study of Columbia University. Two experienced epileptologists classified each individual through review of phenotypic data from standardized telephone interviews and medical record review. Blood samples were obtained from consenting family members, and DNA was purified from blood leukocytes. The Center for Inherited Disease Research (CIDR) provided genotype information for 390 short tandem repeat polymorphisms (STRPs), spaced at an average of 9cM throughout the genome. We used the CIDR markers to screen for linkage across the genome; after obtaining suggestive evidence for linkage we genotyped 29 additional STRP markers for fine mapping on chromosome 6q. We computed 2-point LOD scores using MLINK and multipoint LOD scores using SIMWALK2. We used SIMWALK2 to assemble haplotypes in the region of interest, and used standard methods to sequence all of the exons and exon-intron borders of candidate genes in the region defined by haplotype analysis. Results: This GEFS+ pedigree contains 15 affected individuals across 4 generations: 6 with FS, 5 with FS+ (all of whom also had idiopathic epilepsy), 3 with idiopathic epilepsy, and one with an isolated unprovoked seizure. Evidence was negative for linkage to the regions harboring previously identified GEFS+ genes SCN1B, SCN1A, SCN2A, and GABRG2. We identified a minimal critical region of linkage between markers D6S962 and D6S287, from 6q16.3-22. This was the only region with significant linkage for this pedigree. The maximum multi-point LOD score was 4.67 at markers D6S474 and D6S1706. A haplotype spanning 14.1 cM from 6q16.3-22.31 was shared among all affected individuals and obligate carriers but no unaffected individuals. We sequenced 16 candidate genes selected on the basis of brain expression and predicted function (membrane, transmembrane, and solute carrier proteins) but did not identify a causative mutation. Conclusions: These results provide strong evidence that a novel gene for GEFS+ syndrome lies in this region of chromosome 6q. Since candidate gene sequencing has not yielded a mutation, the gene responsible for the epilepsy syndrome in this family may uncover a mechanism of epileptogenesis distinct from the channelopathies that have been reported to date.