Partial epilepsy with antecedent febrile seizures and seizure aggravation by antiepileptic drugs: associated with loss of function of Na(v) 1.1.
OBJECTIVE
Generalized epilepsy with febrile seizures plus (GEFS+) and severe myoclonic epilepsy in infancy (SMEI) are associated with sodium channel α-subunit type-1 gene (SCN1A) mutations. Febrile seizures and partial seizures occur in both GEFS+ and SMEI; sporadic onset and seizure aggravation by antiepileptic drugs (AEDs) are features of SMEI. We thus searched gene mutations in isolated cases of partial epilepsy with antecedent FS (PEFS+) that showed seizure aggravations by AEDs.


METHODS
Genomic DNA from four patients was screened for mutations in SCN1A, SCN2A, SCN1B, and GABRG2 using denaturing high-performance liquid chromatography (dHPLC) and sequencing. Whole-cell patch clamp analysis was used to characterize biophysical properties of two newly defined mutants of Na(v) 1.1 in tsA201 cells.


RESULTS
Two heterozygous de novo mutations of SCN1A (R946H and F1765L) were detected, which were proven to cause loss of function of Na(v) 1.1. When the functional defects of mutants reported previously are compared, it is found that all mutants from PEFS+ have features of loss of function, whereas GEFS+ shows mild dysfunction excluding loss of function, coincident with mild clinical manifestations. PEFS+ is similar to SMEI clinically with possible AED-induced seizure aggravation and biophysiologically with features of loss of function, and different from SMEI by missense mutation without changes in hydrophobicity or polarity of the residues.


CONCLUSIONS
Isolated milder PEFS+ may associate with SCN1A mutations and loss of function of Na(v) 1.1, which may be the basis of seizure aggravation by sodium channel-blocking AEDs. This study characterized phenotypes biologically, which may be helpful in understanding the pathophysiologic basis, and further in management of the disease.
Liao
Wei-Ping
WP
Institute of Neuroscience and the Second Affiliated Hospital of Guangzhou Medical College, Key Laboratory of Neurogenetics and Channelopathies of Guangdong Province and the Ministry of Education of China, Guangzhou, China. wpliao@tom.com
Shi
Yi-Wu
YW
Long
Yue-Sheng
YS
Zeng
Yang
Y
Li
Tian
T
Yu
Mei-Juan
MJ
Su
Tao
T
Deng
Ping
P
Lei
Zhi-Gang
ZG
Xu
Shu-Jun
SJ
Deng
Wei-Yi
WY
Liu
Xiao-Rong
XR
Sun
Wei-Wen
WW
Yi
Yong-Hong
YH
Xu
Zao C
ZC
Duan
Shumin
S
D000293:Adolescent; D000927:Anticonvulsants / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000503:physiopathology; D053447:Channelopathies / Q000235:genetics* / Q000503:physiopathology; D002648:Child; D004831:Epilepsies, Myoclonic / Q000235:genetics* / Q000503:physiopathology; D004828:Epilepsies, Partial / Q000235:genetics* / Q000503:physiopathology; D004829:Epilepsy, Generalized / Q000235:genetics* / Q000503:physiopathology; D005260:Female; D006801:Humans; D009154:Mutation / Q000235:genetics* / Q000502:physiology; D020125:Mutation, Missense / Q000235:genetics / Q000502:physiology; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology; D010641:Phenotype; D003294:Seizures, Febrile / Q000235:genetics* / Q000503:physiopathology; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D062547:Voltage-Gated Sodium Channel beta-1 Subunit
D000927:Anticonvulsants; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; C470379:SCN1B protein, human; C568251:SCN2A protein, human; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D062547:Voltage-Gated Sodium Channel beta-1 Subunit