ABSTRACT
A follow-up study of a large Utah family with significant linkage to chromosome 2q24 led us to identify a new febrile seizure (FS) gene, SCN9A encoding Na(v)1.7. In 21 affected members, we uncovered a potential mutation in a highly conserved amino acid, p.N641Y, in the large cytoplasmic loop between transmembrane domains I and II that was absent from 586 ethnically matched population control chromosomes. To establish a functional role for this mutation in seizure susceptibility, we introduced the orthologous mutation into the murine Scn9a ortholog using targeted homologous recombination. Compared to wild-type mice, homozygous Scn9a(N641Y/N641Y) knockin mice exhibit significantly reduced thresholds to electrically induced clonic and tonic-clonic seizures, and increased corneal kindling acquisition rates. Together, these data strongly support the SCN9A p.N641Y mutation as disease-causing in this family. To confirm the role of SCN9A in FS, we analyzed a collection of 92 unrelated FS patients and identified additional highly conserved Na(v)1.7 missense variants in 5% of the patients. After one of these children with FS later developed Dravet syndrome (severe myoclonic epilepsy of infancy), we sequenced the SCN1A gene, a gene known to be associated with Dravet syndrome, and identified a heterozygous frameshift mutation. Subsequent analysis of 109 Dravet syndrome patients yielded nine Na(v)1.7 missense variants (8% of the patients), all in highly conserved amino acids. Six of these Dravet syndrome patients with SCN9A missense variants also harbored either missense or splice site SCN1A mutations and three had no SCN1A mutations. This study provides evidence for a role of SCN9A in human epilepsies, both as a cause of FS and as a partner with SCN1A mutations.
Subject(s)
Abnormalities, Multiple/genetics , Epilepsy/complications , Epilepsy/genetics , Seizures, Febrile/etiology , Seizures, Febrile/genetics , Sodium Channels/genetics , Abnormalities, Multiple/physiopathology , Amino Acid Sequence , Amino Acid Substitution/genetics , Animals , Base Sequence , DNA Mutational Analysis , Electroshock , Epilepsy/physiopathology , Female , Gene Knock-In Techniques , Humans , Kindling, Neurologic/physiology , Male , Mice , Molecular Sequence Data , Mutation/genetics , NAV1.1 Voltage-Gated Sodium Channel , NAV1.7 Voltage-Gated Sodium Channel , Nerve Tissue Proteins/genetics , Pedigree , Protein Subunits/genetics , Seizures, Febrile/physiopathology , Sequence Alignment , Sodium Channels/chemistry , SyndromeABSTRACT
The International HapMap Consortium has developed the HapMap, a resource that describes the common patterns of human genetic variation (haplotypes). Processes of community/public consultation and individual informed consent were implemented in each locality where samples were collected to understand and attempt to address both individual and group concerns. Perceptions about the research varied, but we detected no critical opposition to the research. Incorporating community input and responding to concerns raised was challenging. However, the experience suggests that approaching genetic variation research in a spirit of openness can help investigators better appreciate the views of the communities whose samples they seek to study and help communities become more engaged in the science.
