Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy characterized by the onset of prolonged febrile and afebrile seizures in infancy, and evolving to drug-resistant epilepsy with accompanying cognitive, behavioral, and motor impairment. Most cases are now known to be caused by pathogenic variants in the sodium channel gene SCN1A, but several other genes have also been implicated. This review examines current understanding of the role of non-SCN1A genes in DS, and what is known about phenotypic similarities and differences. We discuss whether these are best thought of as minority causes of DS, or as similar but distinct conditions.
Based on a review of literature, a list of genes linked to DS was compiled and PubMed was searched for reports of DS-like phenotypes arising from variants in each. Online Mendelian Inheritance in Man (OMIM) was used to identify further reports relevant to each gene.
Genes that have been reported to cause DS-like phenotypes include SCN2A, SCN8A, SCN9A, SCN1B, PCDH19, GABRA1, GABRG2, STXBP1, HCN1, CHD2, and KCNA2. Many of these genes, however, appear to be associated with their own, different, clinical picture. Other candidate genes for DS have been reported, but there is currently an insufficient body of literature to support their causative role.
Although most cases of DS arise from SCN1A variants, numerous other genes cause encephalopathies that are clinically similar. Increasingly, a tendency is noted to define newly described epileptic disorders primarily in genetic terms, with clinical features being linked to genotypes. As genetic diagnosis becomes more readily available, its potential to guide pathophysiologic understanding and therapeutic strategy cannot be ignored. Clinical assessment remains essential; the challenge now is to develop a gene-based taxonomy that complements traditional syndromic classifications, allowing elements of both to inform new approaches to treatment.