CACNA1G encodes the α1G subunit of T-type calcium channels, which mediate voltage-gated calcium ion entry into excitable cells and regulate calcium-dependent processes including muscle contraction, neurotransmitter release, and gene expression 1. The channel plays critical roles in thalamic and cardiac conduction, regulating thalamocortical pathway function, SA node automaticity, and AV node conduction 2. Pathogenic CACNA1G variants cause spinocerebellar ataxia 42 with neurodevelopmental deficits (SCA42ND), characterized by early-onset cerebellar atrophy and severe intellectual disability 3. Both gain- and loss-of-function variants are implicated in disease: gain-of-function mutations (particularly at the intracellular gate) cause increased calcium current and slower inactivation kinetics, while loss-of-function variants reduce channel activity 3. CACNA1G variants are also associated with absence seizures and schizophrenia risk, with the M1531V variant causing thalamic hyperactivity and abnormal thalamocortical connectivity 2. Loss-of-function variants increase schizophrenia susceptibility through aberrant axonal projections and spontaneous thalamic hyperactivity 2. CACNA1G variants represent a major cause of calcium channelopathy-related intellectual disability 1, with severe-to-profound phenotypes more common in gain-of-function cases. The gene also influences developmental and epileptic encephalopathies through compensatory mechanisms with other voltage-gated ion channels 4. Additionally, the CACNA1G-AS1 long non-coding RNA regulates cancer cell proliferation in diffuse large B cell lymphoma and keloid fibroblasts 56.