A PET-MRI Study of Serotoninergic Brainstem Pathway in Patients With Dravet Syndrome

Overview

Dravet Syndrome (DS) is a severe neurodevelopmental disease, which is predominantly caused by mutations of SCN1A, the gene coding for Nav1.1 voltage-gated sodium channels. DS is characterized by infancy onset, severe cognitive deficit and drug-resistant seizures, including several generalized convulsive seizures per day and frequent status epilepticus, often triggered by fever or hyperthermia. Among the causes of premature deaths in patients with epilepsy, sudden and unexpected death in epilepsy (SUDEP) represents a major cause. SUDEP is a non-traumatic and non-drowning death in patients with epilepsy, unrelated to a documented status epilepticus. The risk of SUDEP is particularly high in patients suffering from DS, reaching about 9/1000-person-year, as compared to about 1/1000-person-year in people with epilepsy including all disease types. The main clinical risk factor of SUDEP is the frequency of convulsive seizures. Beyond improving seizure control, which we showed to mitigate the SUDEP risk, more specific preventive treatment strategies are still lacking. Experimental and clinical data suggest that most SUDEP cases result from postictal brainstem dysfunction, including central respiratory arrest There is a body of evidence suggesting involvement of serotonin (5HT) dysfunction both in the pathogenesis of epilepsy in DS and in seizure-related respiratory dysfunction. Serotonin indeed plays a key role in the regulation of respiration. Population firing of serotoninergic neurons in the medullary raphe is significantly decreased during the ictal and post-ictal periods, in association with decreased breathing and heart rate during and after seizures. Most importantly, post-mortem data in patients, including DS, showed alteration of neuronal populations in the medulla in SUDEP cases with evidence for greater reduction in neuromodulatory neuropeptidergic and monoaminergic, including serotoninergic, systems. SUDEP in DS might therefore be the result of a seizure-induced fatal apnea in a patient who has developed epilepsy-related vulnerability to central respiratory dysfunction favored by 5HT dysfunction. However, several issues remain to be addressed to identify detailed mechanisms and effective therapies. Among them, a key issue is the exact relation between the alterations of the 5HT pathway observed in DS and epilepsy-related respiratory dysfunction In the present study, the hypothesis is that adult patients with DS might demonstrate specific alterations of the 5HT pathway within the brainstem as assessed by PET imaging. The DRAPETOTINE study will thus focus on imaging 5HT brainstem pathway with PET and MRI in patients with DS to assess if abnormalities can be observed and through comparison with data collected in patients drug-resistant focal epilepsy whether these abnormalities are DS specficic or reflect the consequence on brainstem 5HT pathway of refractory seizures. This study will involve 20 adult patients, including 10 adults with established diagnosis of Dravet Syndrome and 10 patients with drug-resistant focal epilepsy. Ten healthy adults will also be included. Participants will be recruited over a period of 18 months and the duration of participation for each participant will be 2 weeks to 8 weeks