Infant sudden death: Mutations responsible for impaired Nav1.5 channel trafficking and function

Area of Science:

• Cardiovascular Genetics
• Molecular Cardiology
• Sudden Death Syndromes

Background:

• Two genetic variants (Q1832E and R1944Δ) in the SCN5A gene, encoding the Nav1.5 sodium channel, were identified in a 5-month-old girl who experienced sudden death.
• The Q1832E variant is a missense mutation previously noted in a Brugada syndrome patient, while R1944Δ is a nonsense mutation causing C-terminal truncation.

Purpose of the Study:

• To investigate the functional relevance of these SCN5A variants in the context of sudden infant death syndrome (SIDS) and Brugada syndrome.
• To determine the impact of individual and combined mutations on Nav1.5 channel function and trafficking.

Main Methods:

• Patch-clamp electrophysiology was used to assess Nav1.5 current density and channel kinetics in transfected HEK-293 cells.
• Biochemical and immunofluorescence techniques were employed to evaluate protein trafficking.
• Genomic DNA sequencing confirmed the variants were in trans.

Main Results:

• The Q1832E mutation significantly reduced Nav1.5 current density and caused severe trafficking defects.
• The R1944Δ mutation had minimal impact on current density and trafficking.
• Coexpression of both variants resulted in a substantial decrease in current amplitude, indicating a combined detrimental effect.

Conclusions:

• The identified SCN5A variants lead to a severely dysfunctional Nav1.5 channel, primarily due to trafficking defects associated with the Q1832E mutation.
• Reduced Nav1.5 current density is a likely contributor to arrhythmogenesis in Brugada syndrome and the sudden death of the SIDS victim.
• These findings highlight the critical role of Nav1.5 channel function in preventing sudden cardiac events in infants.