Novel C1A Domain Variant in Protein Kinase Cγ in Spinocerebellar Ataxia Type 14 Decreases Autoinhibition

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disorder characterized by adult-onset cerebellar ataxia, and occasionally pyramidal signs, cognitive changes, sensory changes, myoclonus, and tremor. SCA14 results from heterozygous gain-of-function pathogenic variants in PRKCG, which encodes protein kinase Cγ. The aim was to elucidate the molecular mechanism of disease in a 60-year-old man with SCA14 due to a novel heterozygous variant in PRKCG c.154T > C p.(C52R). Next-generation sequencing was completed in the proband, targeted variant analysis was conducted in his family, and biochemical functional assays were performed. The C52R variant segregated with disease. Like other C1A domain variants, it had increased basal activity yet was unresponsive to agonist stimulation and was relatively resistant to down-regulation. This expands the genetic landscape of SCA14 and supports the condition as a gain-of-function disease, with variants in the C1A domain having leaky activity yet unresponsiveness to agonist stimulation.