Sodium channel gene family: epilepsy mutations, gene interactions and modifier effects

Disruption of the SCN2A and SCN3A genes in a patient with mental retardation, neurobehavioral and psychiatric abnormalities, and a history of infantile seizures

Mutations in genes encoding voltage-gated sodium channels are significant factors in the etiology of neurological diseases and psychiatric disorders, including various types of idiopathic epilepsy. Using a clinical exon-targeted oligonucleotide array comparative genomic hybridization (aCGH), we have identified a de novo ~110-kb deletion involving exons 1-2 of SCN2A and non-coding exon 1a of SCN3A in a 25-year-old female with mental retardation, neurobehavioral and psychiatric abnormalities, and a history of infantile seizures with abnormal EEG. We propose that haploinsufficiency of SCN2A may play an important role in the genetic basis of neurodevelopmental and neurobehavioral disorders and emphasize the efficacy of detecting exonic copy-number variation (CNV) by exon-targeted oligo aCGH.

Genetic evaluation and counseling for epilepsy

The contribution of genetics to both rare and common epilepsies is rapidly being elucidated, and neurologists are routinely considering genetic testing in the work-up of several epilepsy syndromes of both known and unknown cause. Simultaneously, advances in molecular technology foreshadow additional discoveries in epilepsy etiology, implying a greater role than ever before for genetics in the epilepsy clinic. Genetic testing can be valuable not only for diagnosis but also for guiding treatment and for informing reproductive choices. In this Review, we outline the principles of genetic evaluation and counseling, and describe how to interpret genetic test results for epilepsy in the following five common clinical scenarios: Dravet syndrome, infantile spasms, epilepsy with cortical malformation, epilepsy with mental retardation, and idiopathic epilepsy syndromes. We differentiate clinical situations in which genetic testing is of high and low utility, and predict future areas for the application of genetics in epilepsy practice.

Neurological channelopathies: new insights into disease mechanisms and ion channel function

Inherited mutations of ion channels provide unique insights into the mechanisms of many neurological diseases. However, they also provide a wealth of new information on the fundamental biology of ion channels and on neuron and muscle function. Ion channel genes are continuing to be discovered by positional cloning of disease loci. And some mutations provide unique tools to manipulate signalling cascades, which cannot be achieved by pharmacological intervention. Here we highlight some unanswered questions, and some promising areas for research that will likely lead to a fuller understanding of the link from molecular lesion to disease.