Screen For SCN1A Mutations In Patients With Partial Epilepsy With FS Plus And Splicing Assay Of The Intronic Mutations In Vitro

PurposeTo screen SCN1A mutations in patients with partial epilepsy with febrile seizures plus(PEFS+)and investigate the mechanism of intronic mutations effecting on precursor mRNA(pre-mRNA) splicing. To characterize SCN1A mutations of PEFS+ and discuss the possibility that PEFS+ is a distinct phenotype of SCN1A mutation and different from both Dravet syndrome (DS) and generalized epilepsy with febrile seizures plus (GEFS+).Patients and methods37 patients with PEFS+ were collected. All the 26 exons and splicing regions of SCN1A were screened with denaturing high performance liquid chromatography (DHPLC) and direct sequencing. A splicing assay by mini-gene construction was conducted to determine the effect of the c.473+5 G>A and c.473+110A>G mutation on pre-mRNA splicing. All the update SCN1A mutations which were identified in PEFS+ patients had been reviewed to detect a common feature and to find the relationship between PEFS+,GEFS+ and DS. Results4 heterozygous mutations were detected: c.473+5 G>A,c.473+110 A>G,c.1028+35 T>C,c.2378 C>T. The splice site mutation c.473+5 G>A could disrupt normal splcing and finally result in a truncation of SCN1A. The intron mutation c.473+110 A>G did not effect on splicing. 20 SCN1A mutations in PEFS+ were reviewed and PEFS+ was mainly induced by missense mutations. 52% of these mutations located in the S4-S6 segments. The proportion of mutations in the S4-S6 segments in PEFS+ is much higher than GEFS+(27.3%) and close to DS(60.2%). Splicing-site mutation and frame-shift mutation could also lead to PEFS+,but they were not the main mutation types for PEFS+.ConclusionSCN1A is a candidate gene for PEFS+. Missense mutation of SCN1A is the most common mutation type for PEFS+. Most of missense mutations in PEFS+ were located in the S4-S6 segments. Splicing-site mutations and frame-shift mutations were also related to PEFS+. The pathogenesis of intron mutations for PESF+ was to result in SCN1A truncation by altering splicing sites of SCN1A pre-mRNA. According to the mutation characteristics, PEFS+ seems to be a transition phenotype between DS and GEFS+.