Abstract
Febrile Seizures (FS) are the most common seizure type in children and recurrent FS are a risk factor for developing temporal lobe epilepsy (TLE). Although the mechanisms underlying FS are largely unknown, recent family, twin and animal studies indicate that genetics are important in FS susceptibility. A forward genetic strategy
... read more
was used employing mouse chromosome substitution strains (CSS) to identify novel FS susceptibility quantitative trait loci (QTLs). FS were induced by exposure to warm air at postnatal-day-14. Video-EEG monitoring identified tonic-clonic convulsion onset, defined as febrile seizure latency (FSL), as reliable phenotypic parameter to determine FS susceptibility. FSL was determined in both sexes of the host strain (C57BL/6J), the donor strain (A/J) and each CSS. C57BL/6J mice were more susceptible to FS than A/J mice. Phenotypic screening of the CSS panel identified six strains (CSS1, -2, -6 -10, -13 and -X) carrying QTLs for FS susceptibility. The QTLs for FS susceptibility were mapped on chromosome 1 (QTL1a, 1b), 2 (QTL2a, 2b) and X. After haplotype mapping and bioinformatics we selected candidate genes in each QTLs for sequence, expression analysis and functional interference studies. In QTL1b, the Srp9 (signal recognition particle 9) gene showed reduced brain mRNA expression in CSS1 compared to C57BL/6J. The CSS1 phenotype (reduced susceptibility to experimental FS) could be induced in C57BL/6J mice by partial knock-down of Srp9 expression with antisense oligonucleotides or by reduction of protein translation by pretreatment with cycloheximide or rapamicin in vivo. In TLE patients we found higher hippocampal SRP9 expression in patients with antecedent FS than in patients without FS. Our results identify Srp9 as a febrile seizure susceptibility gene and implicate SRP-regulated translation and endoplasmic reticulum (ER) stress in the mechanism of febrile seizures. QTL2a is homologous to the human FEB3 locus, containing the sodium channel subunit genes Scn1a, Scn2a, Scn3a and Scn9a. QTL2b harbors the pyrogenic Il1b gene and the Srp14 gene, a key component of the ubiquitous signal recognition particle. Sequencing of Il1b did not reveal any genetic variation between the parental strains of the CSS panel. Moreover, manipulation of IL1B levels in C57BL/6J and CSS2 mice did not affect FS susceptibility. Hippocampal Srp14 mRNA expression was found to be up-regulated in CSS2 mice compared to C57BL/6J. Interestingly SRP14 forms a dimer with SRP9. This is the first data set using CSS to screen for a seizure trait in mouse pups. It provides evidence for common FS susceptibility QTLs, which was used to identify FS susceptibility genes. The identification of a mouse QTL homologous to the human FEB3 locus is strong support for the validity of the experimental FS model to study genetics of FS in human. Identification of genes and pathways involved in FS seizure susceptibility may help to identify biomarkers for the early diagnosis of children at risk for complex FS and TLE. Indeed, SRP9 and SRP14 are excellent candidate biomarkers. These studies provide insight in the mechanisms underlying human FS and provide new handles for the development of new treatment strategies for FS and TLE.
show less
