The seizures started when Samantha Gundel was just four months old. By her first birthday, she was taking a cocktail of three different anticonvulsant medicines. A vicious cycle of recurrent pneumonia, spurred on by seizure-induced inhalation of regurgitated food, landed the young toddler in and out of the hospital near her Westchester County home in New York State.
Genetic testing soon confirmed her doctors’ suspicions: Samantha, now age 4, has Dravet syndrome, an incurable form of epilepsy. Her brain was misfiring because of a mutation that is unlike those responsible for most genetic diseases; it’s a type that has long eluded the possibility of correction. Available drugs could help alleviate symptoms, but there was nothing that could address the root cause of her disease.
That’s because the mutation at the heart of Dravet creates a phenomenon known as haploinsufficiency, in which a person falls ill if they have only a single working copy of a gene. That lone gene simply can’t produce enough protein to serve its molecular purpose. In the case of Dravet, that means that electrical signaling between nerve cells gets thrown out of whack, leading to the kinds of neuronal shock waves that trigger seizures.
Most genes are not like this. Though the human genome contains two copies of almost every gene, one inherited from each parent, the body can generally do fine with just one.
Not so for genes such as SCN1A, the main culprit behind Dravet. For SCN1A and hundreds of other known genes like it, there’s a delicate balance of molecular activity that is needed to ensure proper function. Too little activity is a problem — and oftentimes, so is too much.
