Which of the following statements best explains the pathophysiology of Dravet Syndrome related to the SCN1A gene?

Question

BlackTom AI · Accepted Answer

Question restated:
Which statement best explains the pathophysiology of Dravet Syndrome related to the SCN1A gene?

Option 1: 'SCN1A mutations increase potassium channel activity, leading to enhanced neuronal repolarization.'
This option is incorrect because SCN1A encodes a voltage-gated sodium channel (NaV1.1), not a potassium channel. Its mutations do not increase potassium channel activity; rather, the pathology involves impaired sodium current in certain neuronal populations. The idea of enhanced repolarization would generally reduce excitability, which contradicts the hyperexcitability seen in Dravet Syndrome.

Option 2: 'SCN1A encodes the Naᵥ1.1 subunit primarily expressed in inhibitory interneurons, and its dysfunction leads to network hyperexcitability.'
This statement accurately reflects current understanding. SCN1A encodes the NaV1.1 sodium channel subunit, with high expression in inhibitory interneurons. Loss-of-function mutations reduce sodium currents in these interneurons, diminishing GABAergic inhibition, which disinhibits networks and promotes hyperexcitability and seizures characteristic of Dravet Syndrome.

Option 3: 'SCN1A encodes a subunit of a voltage-gated sodium channel critical for excitatory neurons; mutations lead to their hyperexcitability.'
This is misleading. While SCN1A is a sodium channel subunit, its critical pathogenic effect in Dravet is through impaired function in inhibitory interneurons, not primarily excitatory neurons. If excitatory neurons were the only affected, the net effect on network excitability and seizure phenotype would not align with the typical inhibitory interneuron dysfunction seen in Dravet.

Option 4: 'SCN1A encodes a chloride channel responsible for inhibitory GABAergic signaling, and its mutation reduces GABA synthesis.'
This option misidentifies SCN1A as a chloride channel and incorrectly links mutations to reduced GABA synthesis. SCN1A does not encode a chloride channel nor directly regulate GABA synthesis. The established mechanism involves sodium channel dysfunction in interneurons, leading to reduced inhibitory control rather than altered GABA synthesis per se.

Summary of the reasoning pattern:
- We first check what SCN1A encodes and which neuronal populations it primarily affects. The core idea is that loss-of-function in NaV1.1 in inhibitory interneurons reduces inhibition, causing network hyperexcitability and seizures. 
- We evaluate each option against this mechanism, identifying inaccuracies such as misidentifying the channel type (potassium vs sodium), the neuronal compartment (inhibitory interneurons vs excitatory neurons), or the downstream effect (GABA synthesis vs GABAergic activity).
- The option that aligns with the established pathophysiology accurately states that SCN1A encodes NaV1.1, predominantly expressed in inhibitory interneurons, and that its dysfunction leads to disinhibition and network hyperexcitability, matching Dravet Syndrome pathology.

NEUR20001_2025_SM2 Assessment for Workshop 7

Which of the following statements best explains the pathophysiology of Dravet Syndrome related to the SCN1A gene?

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