CACNA1I gain-of-function mutations differentially affect channel gating and cause neurodevelopmental disorders

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• T-type calcium channels (Cav3.1–Cav3.3) are crucial for neuronal excitability, regulating functions like sensory processing and sleep.
• The CACNA1I gene encodes the Cav3.3 channel, implicated in various physiological processes.

Observation:

• Four heterozygous missense variants in CACNA1I were identified in patients with neurodevelopmental phenotypes.
• Specific variants (p.Ile860Met, p.Ile860Asn, p.Ile1306Thr, p.Met1425Ile) were found in individuals with cognitive impairment, developmental delay, seizures, hypotonia, and epilepsy.
• Patch-clamp analysis and structure modeling revealed that these mutations alter Cav3.3 channel gating kinetics and voltage-dependence.

Findings:

• Mutations in Cav3.3 channels result in slowed activation, inactivation, and deactivation kinetics.
• The variants cause hyperpolarizing shifts in voltage-dependence, leading to increased window currents and elevated calcium influx.
• These alterations result in a gain-of-function effect, increasing neuronal excitability and potentially causing calcium toxicity.

Implications:

• CACNA1I gain-of-function mutations are implicated in a spectrum of neurodevelopmental disorders.
• Altered Cav3.3 channel function can lower neuronal firing thresholds and increase firing frequency, potentially explaining epilepsy.
• The study highlights Cav3.3 channel dysfunction as a molecular mechanism underlying diverse neurodevelopmental phenotypes.