Epilepsy phenotype associated with a chromosome 2q24.3 deletion involving SCN1A: Migrating partial seizures of infancy or atypical Dravet syndrome?

The deletion of a sodium channel gene cluster located on chromosome 2q24.3 is associated with variable epilepsy phenotypes, including Dravet syndrome and migrating partial seizures of infancy. Although SCN1A is considered as the major contributor to the epilepsy phenotype, the role of other sodium channel genes that map within this cluster has not been delineated. We presented five new cases with a chromosome 2q24.3 deletion involving SCN1A and investigated their epilepsy phenotype in relation to the extent of the deletion. Three cases with deletion of the whole sodium channel gene cluster (SCN3A, SCN2A, SCN1A, SCN9A, and SCN7A) exhibited a complex epilepsy phenotype that was atypical for Dravet syndrome and suggestive of migrating partial seizures of infancy: early seizure onset (before 2 months of age), severe developmental delay from seizure onset, multifocal interictal spikes, polymorphous focal seizures, and acquired microcephaly. Two cases with partial deletion of SCN1A and SCN9A and whole SCN1A deletion had an epilepsy phenotype of Dravet syndrome. A literature review of cases with chromosome 2q24.3 deletion revealed that, in most Dravet syndrome cases, it does not involve SCN2A and SCN3A, whereas a complex epilepsy phenotype that is shared with migrating partial seizures of infancy was associated with cases of deletion of the whole sodium channel gene cluster.