In most cases, mutations in the SCN1A gene occur “de novo”. It means that neither the father nor the mother carry the mutated gene. The mutation arises spontaneously before conception or at the time of conception; boys and girls are equally affected. The mutated gene has not been inherited.
If your child carries a SCN1A de novo mutation, based on our current understanding, the risk to have another affected child is the same as in the general population (i.e. 1:20,000-1:40,000 births). For your older children, there is no risk for them to be affected by Dravet syndrome. No one is to blame. You should not feel guilty nor responsible for your child’s disease.
You may wonder if an SCN1A mutation always means Dravet syndrome. Actually SCN1A mutations can also be found in patients with other types of epilepsy, such as GEFS+ syndrome. GEFS+ stands for “Genetic Epilepsy with Febrile Seizures +” characterising families where different members from different generations suffer from a milder form of epilepsy.