Dravet Syndrome Model (mouse)
Dravet syndrome (DS) is a rare pharmacoresistant epilepsy disorder with devastating consequences that occurs in 1/20,000 to 1/40,000 people. DS appears during the first year of life in a normally developing child and the first sign of DS is seizures that are usually induced by a fever or increase in body temperature due to other reasons such as hot baths. Spontaneous, recurrent seizures begin occurring within weeks of the initial seizure, becoming progressively worse and occurring more frequently. In addition to seizures, DS is associated with comorbidities such as ataxia, sleep problems, and cognitive impairment. DS seizures are highly resistant to currently available treatments and seizure freedom is rare, therefore identification of an optimal treatment that effectively treats seizures and comorbidities is crucial.
In 80 percent of DS cases, the disease is caused by a loss-of-function mutation in the SCN1A gene, which encodes for the voltage-gated sodium channel Nav1.1. The Scn1aWT/A1783V knock-in mutation mice exhibits DS-like phenotypes, including hyperthermia-induced and spontaneous recurrent seizures, as well as comorbidities like ataxia (Kuo et al., 2019; Ricobaraza et al., 2019). The mutation mini-cassette includes lox P sites and, in the presence of Cre recombinase, results in an amino-acid substitution from alanine to valine at position 1783 (A1783V), previously reported in patients with DS (Lossin, 2009; Klassen et al., 2014). This model is easy to breed and is readily available from Jackson Laboratories (Bar Harbor, ME, U.S.A.), Jax stock #026133 for the male floxed stop Scn1aWT/A1783V and Jax stock #8454 for the female Sox2-Cre+.
For induction of hyperthermia-seizures, mice are placed under a heat lamp and the core body temperature is gradually increased (1°C / 2 min) until a generalized seizure is observed or the temperature reaches 42.5°C (Pernici et al., 2020). If no seizure occurs at 42.5°C the mouse is considered protected. After the procedure, mice are put on a cool, granite block to quickly bring the core body temperature down and then returned to their home cages. Body temperature is monitored using a neonate rectal probe (Braintree Scientific Inc) coupled to a TCAT-2DF controller (Physitemp Instruments). Test compound will be administered and tested at time-of-peak effect (TPE) of a drug determined based on available information (activity in other seizure models, and pharmacokinetic data – if available). Male and female Scn1aA1783V/WT mice (n = 10 in vehicle and drug treatment group) that are 5-10 weeks old are randomly assigned to drug or vehicle group and the staff are blinded to the treatment. The temperature at which mice seize is recorded. If the animal seizes at the time of injection or before the test, it is not used in the test. To test multiple doses of a single compound mice are tested once a week with a single dose over four weeks. Data is presented as a temperature change to event analysis curve with percent of animals not seizing against temperature of seizure, and significant difference between the vehicle and the compound is assessed. Any adverse effects, including deaths, are noted.