Epilepsy Flashcards
prevalence and life time risk of epilepsy
- Affects approx. 1% of the population.
- Lifetime risk of having a seizure ~10%
gene therapy for refractory epilepsy:
2 potenital roles:
- Adjustment of excitation-inhibition balance in focal epilepsies – with improved regional, cell-type and temporal specificity (focal epilepsies)
- Correction or mitigation of underlying molecular defect in genetic epilepsies. – monogenic causes of epilepsy are extremely rare – there are about 50 different ones of these, but to effect or mitigate these epilepsies would affect a v small proportion of the epilepsy population.
Types of RNA therapy
- Antisense oligonucleotides
a. These distribute more broadly in the brain – so can deliver using less invasive routes.
b. ASOs can be delivered intrathecally and so are more suited to generalised epilepsies. - RNA interference:
a. miRNA: microRNA (non-coding RNAs that normally regulate gene expression)
b. shRNA: small hairpin RNA
c. siRNA: small interfering RNA (double-stranded RNA)
d. RISC: RNA-induced silencing complex
how do AEDs work
by potentiating GABAergic inhibition and potassium channel function, or by inhibiting sodium channels or glutamate receptors.
Candidate target genes in epilepsy (4)
Kv1.1 – potassium channel
eGluCL – non-mammalian glutamate gated chloride channel
hM4Di - synthetic receptor
Y2 receptor - neuropeptide receptor for NPY
Constitutive gene therapy using KCNA1:
Overexpression of Kv1.1 to reduce neuronal excitability and neurotransmitter release.
- Receptor is widely expressed in the brain, and mainly found in axons.
- Kv1.1 governs the duration of AP – it helps repolarise the membrane potential during the AP.
- If you overexpress the WT there isa graded reduction of excitability and NT release
Neuropeptides released in excess following epileptic activity (3)
- Neuropeptide Y
- Galanin
- Dynorphin
Neuropeptides have diffuse, often inhibitory actions, and are preferentially released from nerve terminals by intense activity:
NPY co-expression with Y2 receptors:
- Complex as NPY acts on both pro-excitatory and pro-inhibitory (e.g. Y2) receptors.
To overcome this, they co-express both the neuropeptide to increase amount of NPY release but also with the inhibitory peptide to prevent this simultaneous accelerate and brake you would get just from just expressing NPY.
- You can suppress seizures.
Chemogenetics
- Gene therapy to express a designer receptor exclusively activated by a designer drug.
- Transduced neurons are functionally normal in the absence of the Designer Drug
- Designer Drug acts exclusively on neurons expressing the DREADD to suppress seizures.
- You can give drug continuously or on demand.
DREADD: hM4D(Gi)
- Human muscarinic 4 receptor – Gi (Gi-protein cascade)
- DREADD – designer receptor, exclusively activated by designer drug.
- Only 2 amino acids different from human M4 receptor
- Insensitive to ACh – made insensitive to its normal ligand.
- Hyperpolarises neurons and inhibits NT release.
- Animals treated with this DREADD gene therapy you can suppress excitability on demand.
On-demand seizure suppression with hM4D(Gi)
OLANZAPINE
Olanzapine immediately suppressed seizures in a post-kainate model of TLE.
What is the control drug used for epilepsy studies
GFP
Activity-dependent promoters for closed-loop:
- cFos is an immediate early gene that switches on following seizures
- closed-loop gene therapy: cFos promoter driving KCNA1.
- cFos is a marker of neuronal activity, immediate early egne that acts as transcription factors and controls expression of other genes.
- Took the promoter for cFOS (increases expression) and drove Kv1.1/KCNA1 under the control of cFos promoter. This was highly effective.
WHAT is DS
- A severe developmental epileptic encephalopathy
Caused by haploinsufficiency (LoF) mutations in SCN1A (Nav1.1) in 80% of cases.
RNA therapies for genetic epilepsy:
Using ASO to treat GoF disease: e.g. SCN2A.
- At a cellular level it is decreasing the level of sodium channel expression and therefore reducing the amount of action potentials being generated in response to current injection.
- This is very good! But the disease is incredibly rare.
