The minimal prevalence of SCN1A mosaic deletion is estimated to be 0.9% (95% confidence level: 0.11-3.11%) of DS with negative for SCN1A and PCDH19 mutations.
We screened for PCDH19 mutations in 75 girls diagnosed with Dravet syndrome (DS) without a SCN1A mutation and 29 girls with fever-sensitive and cluster seizures.
Basing on the numerous similarities between DS and PCDH19-related epilepsy, we tried stiripentol in a nine and half year old female patient with PCDH19-related resistant epilepsy, as add-on treatment to valproate and clobazam.
Recently, PCDH19-related EIEE turned out to be more frequent than initially thought, contributing to around 16% of cases (25% in female groups) in the SCN1A-negative DS-like patients.
Underlying causes were identified in 15 children (65%) and included SCN1A-related Dravet syndrome (formerly severe myoclonic epilepsy of infancy) or genetic epilepsy with febrile seizures plus syndrome (n = 8 and n = 1, respectively), a protocadherin 19 mutation, a 1qter microdeletion, neuronal migration disorders (n = 2), and other monogenic familial epilepsy (n = 2).
The second most important Dravet-associated gene is PCDH19.These patients initially may have all characteristics of Dravet syndrome but may later run a somewhat different course.