Mechanism of action
The end of an  axon is enlarged –  the presynaptic button. Next to the presynaptic button there is a space called the  synaptic cleft (space between the neurons). On the other side of the synaptic cleft is the part of a  dendrite that receives messages – the  postsynaptic button. The presynaptic button at the end of the axon contains  vesicles filled with chemical messengers, called neurotransmitters. The postsynaptic button is covered by  receptors for these messengers.
When the nerve impulse arrives in the presynaptic button, the vesicles filled of neurotransmitters move down towards the  presynaptic membrane and are released in the synaptic cleft.
The neurotransmitters cross the synaptic cleft and bind to the receptors on the postsynaptic button.
This binding enables the nerve impulse to continue its course into the new neurone through its dendrite.
70% of Dravet syndrome patients have a mutation in the SCN1A gene located on chromosome 2.
The SCN1A gene determines how postsynaptic membrane receptors work.
The alteration (mutation) of the SCN1A gene modifies how the gene works. This proper working modification leads to epilepsy.
For Dravet syndrome patients this mutation is nearly always de novo, meaning that the parents did not pass it on to their child. The mutation occurred in the embryo during its intra-uterine life and no other member of the family should be affected. There are rare exceptions to this statement; therefore careful genetic counselling is worthwhile.
About 70% of Dravet syndrome patients have a SCN1A gene mutation. Therefore around 30% of patients, clinically diagnosed with a Dravet syndrome may carry mutation on other genes.
Recently in 8% of SNC1A negative patients diagnosed as Dravet syndrome, the mutation of the PCDH19 gene on the X chromosome has been identified. Most of these patients are female.
Research is on-going to determine the « how » of the altered PCDH19 gene leads to epileptic seizures.
Twenty to thirty per cent of diagnosed Dravet patients do not carry the SCN1A mutation. Research is ongoing worldwide in order to look for other genes and/or factors which may be linked to this type of epilepsy.