Borderline Dravet syndrome: a useful diagnostic category?

The term "borderline" severe myoclonic epilepsy of infancy (SMEIB) has been used to designate patients in whom myoclonic seizures or generalized spike and wave activity are absent. It has also been used loosely to indicate mild forms of the syndrome. It is now acknowledged that the course and outcome of patients with SMEIB are the same as in the core syndrome. The rate of patients exhibiting SCN1A gene mutations is also similar, and it has been observed that the same mutations can cause both typical and "borderline" forms, indicating causal homogeneity. Defining a borderline form of a syndrome would mean setting the criteria of semiology and severity whereby a given phenotype falls within and outside the core syndrome. Such process has never been made for Dravet syndrome and is of course unrealistic in view its polymorphic expression. The eponym Dravet syndrome has been preferred to designate a syndrome spectrum that also embraces SMEIB. Therefore the term "borderline" Dravet syndrome is improper. The definition "mild form" of Dravet syndrome would certainly be more suitable to indicate those patients exhibiting a less severe or incomplete form of the syndrome. Variability in severity favors the concept that SCN1A loss of function causes a spectrum of epilepsy phenotypes in which seizures, often prolonged and precipitated by fever, are the prominent feature and schematic subdivisions would be inappropriate, at least in the early stages. An initial definition of SCN1A gene-related epilepsy would perhaps be more suitable when a mutation of this gene is ascertained and the clinical picture is still ill defined.