Expanded clinical phenotype spectrum correlates with variant function in SCN2A-related disorders

Area of Science:

• Neurogenetics
• Channelopathies
• Developmental Neuroscience

Background:

• SCN2A-related disorders involve the voltage-gated sodium channel Nav1.2, leading to diverse clinical presentations including epilepsy and autism.
• These rare disorders exhibit significant clinical heterogeneity, complicating diagnosis and treatment.

Purpose of the Study:

• To systematically phenotype 81 patients with SCN2A variants and assess Nav1.2 channel function.
• To understand the relationship between clinical phenotypes, disease severity, and specific SCN2A variant functions.

Main Methods:

• Systematic phenotyping of 81 patients with 69 unique SCN2A variants.
• Assessment of Nav1.2 channel function for each variant.
• Correlation analysis between primary phenotype, non-seizure severity index, and variant function.

Main Results:

• A strong correlation was found between primary phenotype (epilepsy onset, autism) and non-seizure severity (P = 0.002).
• Phenotype also strongly correlated with variant function (P < 0.0001), with gain-of-function in neonatal epilepsy and loss-of-function in later-onset epilepsy and autism.
• Cluster analysis identified five distinct patient groups based on phenotype and variant function.

Conclusions:

• The clinical expression of SCN2A variants is influenced by developmental factors, linked to Nav1.2 channel function.
• Non-seizure severity depends on seizure onset age and variant function, crucial for developing targeted SCN2A therapies.