In most cases the mutations in<unk>  are not hereditary and the mutated gene is found for the first time in a single family member. In 70–90% of patients,<unk>  is caused by nonsense mutations in the SCN1A gene resulting in a premature stop codon and thus a non-functional protein. This gene normally codes for neuronal voltage-gated sodium channel Nav1.1. In mouse models, these loss-of-function mutations have been observed to result in a decrease in sodium currents and impaired excitability of GABAergic interneurons of the hippocampus. The researchers found that loss of Nav1.1 channels was sufficient to cause the epilepsy and premature death seen in<unk> . The timing of the first signs and symptoms in<unk>  occur about the same time as normal childhood vaccinations, leading some to believe the vaccine was the cause. However, this is likely a non-specific response to fever, as vaccination often induces fever, and fever is known to be associated with seizures in persons with<unk> . Some of the patients who put forth vaccine injury claims from encephalopathy were later found, upon testing, to actually have<unk> . Genetics The genotypic explanation of the disorder has been located on the specific voltage-gated sodium channel genes known as SCN1A and SCN2A. These genes are located on the long (q) arm of chromosome 2 at position 24.3 and code for the alpha subunit of the transmembrane sodium channel protein. A mutation in either of these two genes will cause an individual to develop dysfunctional sodium channels, which are crucial in the pathway for sending chemical signals in the brain, causing the phenotypic display of myoclonic epilepsy from the individual. A properly functioning channel would respond to a voltage difference across the membrane and form a pore through which only sodium ions can pass. The influx of sodium induces the generation of action potential by temporarily changing the charge of the cell. When the gene is mutated, the eventually translated protein improperly folds its pore segment within the cell membrane because it has different amino acid chemistry, which renders the channel inactive. It is also possible for a mutation to reduce the number of channels produced by an individual, which leads to the development of<unk> . Currently, the SCN1A gene is the most clinically relevant; the largest number of epilepsy related mutations characterized thus far occur in this gene. Typically, a missense mutation in either the S5 or S6 segment of the sodium channel pore results in a loss of channel function and the development of<unk> . A heterozygous inheritance of an SCN1A mutation is all that is necessary to develop a defective sodium channel; patients with<unk>  will still have one normal copy of the gene.
Dravet syndrome
Stratton Parker syndrome
De Barsy syndrome
Rett syndrome
Shapiro syndrome
Catel–Manzke syndrome
Benedikt syndrome
Huntington's disease-like syndrome