Spinocerebellar ataxia type 14 (SCA14) is a rare autosomal dominant neurodegenerative disorder caused by mutations in the PRKCG gene, which encodes protein kinase Cγ (PKCγ). The clinical manifestations are heterogeneous, ranging from slowly progressive pure cerebellar ataxia to complex phenotypes with sensory or extrapyramidal involvement. To the best of our knowledge, the present report is the first to describe a Han Chinese family carrying the PRKCG c.424T>G (p.C142G) mutation, which has previously only been described in Danish and Japanese cohorts. The proband, a 72-year-old man, developed gait instability in his 40s, progressing to dysarthria, intention tremor, oculomotor slowing and sensory impairment. Brain MRI revealed severe diffuse cerebellar atrophy. The siblings and daughter of the patient presented with variable ataxic symptoms, confirming autosomal dominant inheritance. Genetic testing by next-generation sequencing identified the heterozygous c.424T>G mutation, co-segregating in affected family members. This mutation localizes to the C1 regulatory domain of PKCγ, a zinc-finger structure critical for diacylglycerol binding and kinase autoinhibition. Substitution of cysteine by glycine at codon 142 destabilizes zinc coordination, impairs protein stability and disrupts membrane recruitment. Functional evidence suggests that C142G induces aberrant kinase activity, misfolding and altered MAPK signaling, resulting in chronic cellular stress without rapid neuronal death, thus accounting for the indolent course of the disease compared with that of polyglutamine SCAs. The present findings expand the knowledge regarding the ethnic and geographic distribution of the codon 142 mutation and highlight the complexity of genotype-phenotype associations, as clinical presentations varied from mild gait ataxia to cognitive impairment and bulbar involvement. The report underscores the value of early genetic testing in unexplained ataxia, facilitating accurate diagnosis, genetic counseling and individualized management. Further functional studies are warranted to clarify the pathogenic mechanisms and to explore potential targeted therapies for SCA14.

Spinocerebellar ataxia (SCA) is an autosomal dominant neurodegenerative disorder marked by progressive loss of cerebellar function. Over 40 genetically defined SCA subtypes have been identified, arising from mechanisms such as cytosine-adenine-guanine (CAG) trinucleotide repeat expansions, point mutations, and gene deletions. Spinocerebellar ataxia type 14 (SCA14) stems from mutations to the protein kinase C gamma (PRKCG) gene, which codes for protein kinase C gamma (PKCγ), a signaling protein predominantly expressed in cerebellar Purkinje cells. Although the genetic basis of SCA14 is well established, the mechanisms driving Purkinje cell dysfunction remain poorly understood. Notably, transgenic mice expressing the common PKCγ-Gly118Asp (G118D) mutation, located in the protein's regulatory domain, do not exhibit an overt disease phenotype, raising questions about potential compensatory changes at the molecular level. We examined the expression of regulator of G protein signaling 8 (Rgs8), a molecule implicated in SCA-related pathways. Organotypic slice cultures and primary cerebellar cell cultures were generated in vitro to assess Purkinje cells from the non-manifesting PKCγ-G118D transgenic mouse line. A significant increase in Rgs8 expression was observed in both slice cultures and primary cerebellar cell cultures derived from the non-manifesting SCA14 mouse line. Elevated Rgs8 expression in Purkinje cells from symptom-free PKCγ-G118D mice suggests molecular adaptations that may underlie the non-manifesting phenotype, offering insight into the subclinical SCA14 pathophysiology.

Spinocerebellar ataxia (SCA), an autosomal dominant neurodegenerative condition, is marked by a gradual deterioration of cerebellar function. To date, more than 40 distinct SCA subtypes have been identified, with some attributed to CAG repeat expansions and others to point mutations or deletions. Among these, spinocerebellar ataxia type 14 (SCA14) stems from missense mutations or deletions within the PRKCG gene, encoding protein kinase C gamma (PKCγ), a pivotal signaling molecule abundant in Purkinje cells. Despite its significance, the precise mechanisms underlying how genetic alterations trigger Purkinje cell malfunction and degeneration remain elusive. Given the prominent role and high expression of PKCγ in Purkinje cells, SCA14 presents a unique opportunity to unravel the underlying pathogenesis. A straightforward hypothesis posits that alterations in the biological activity of PKCγ underlie the disease phenotype, and there are hints that mutated PKCγ proteins exhibit altered enzymatic function. Our prior research focused on the PKCγ-G118D mutation, commonly found in SCA14 patients, located in the regulatory domain of the protein. While cellular assays demonstrated enhanced enzymatic activity for PKCγ-G118D, transgenic mice carrying this mutation failed to exhibit suppressed dendritic development in cerebellar cultures, raising questions about its impact within living Purkinje cells. One hypothesis is that endogenous PKCγ might interfere with the expression or effect of PKCγ-G118D. To further investigate, we leveraged CRISPR-Cas9 technology to generate a PKCγ knockout mouse model and integrated it with an L7-based, Purkinje cell-specific transfection system to analyze the effects of G118D protein expression on the dendritic morphology of developing Purkinje cells. Our findings reveal that, utilizing this approach, PKCγ-G118D exerts a detrimental effect on Purkinje cell growth, confirming its negative influence, indicating that the potential of the G118D mutation to contribute to SCA14 pathogenesis.

Spinocerebellar ataxia type 14 (SCA14) is an autosomal-dominant disorder caused by more than 80 PRKCG missense variants encoding protein kinase Cγ (PKCγ), a serine/threonine kinase highly enriched in Purkinje cells (PCs). Despite typically late onset and slow progression, the molecular basis of age-related decline remains unclear. We used a somatic in vivo approach to express wild-type (WT) PKCγ-GFP or the prototypical G128D PKCγ-GFP selectively in PCs of neonatal mice via an adeno-associated virus (AAV) under a PC-specific promoter. G128D PKCγ-GFP formed cytoplasmic aggregates, mislocalized PCs during development, and produced gait deficits by 4 weeks that worsened with age, despite preserved PC counts and overall cerebellar volume at 1.5 years. Immunohistochemistry revealed a selective vulnerability of climbing-fiber (CF) input: vesicular glutamate transporter 2 (VGLUT2), a marker of CF synapses, declined significantly from 12 to 60 weeks in G128D mice, and the VGLUT2-positive innervation field was narrower than age-matched WT at both time points. By contrast, the glutamate/aspartate transporter GLAST in Bergmann-glial radial processes was reduced predominantly at 12 weeks in G128D mice. The δ2 glutamate receptor (GluD2) at parallel fibers and glial fibrillary acidic protein (GFAP) decreased with age but were comparable between expression conditions. Notably, aggregated mutant PKCγ accumulated within the axon initial segment (AIS), whose architecture progressively deteriorated; the altered AIS excluded PKCγ-GFP from distal axons and, by 60 weeks, was associated with reduced delivery of the vesicular GABA transporter (VGAT) to deep cerebellar nuclei (DCN), consistent with impaired anterograde transport. Hence, rather than overt neuronal loss, the cumulative burden of G128D-specific CF/axonal deficits and age-accentuated circuit and glial changes-reduced GLAST function and decreased GluD2-accounts for the worsening motor phenotype. This AAV-based system provides a practical platform to dissect late-onset pathogenic mechanisms and evaluate therapeutic strategies in vivo.

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant disorder characterized by progressive cerebellar dysfunction and neurodegeneration. To date, it is rarely reported in China. SCA14 is caused by mutations in the PRKCG gene, which encodes protein kinase C gamma (PKCγ). Although nearly eighty distinct mutations of PRKCG gene have been identified, the pathological mechanisms of SCA14 remain unclear. In this study, we performed whole exome sequencing to screen causative genes in patients with unexplained progressive cerebellar ataxias, and identified three PRKCG mutations (c.302A > G, p.H101R, c.520C > G, p.H174D and c.2063C > G, p.P688R) that have not been previously reported in Chinese patients with SCA14. To explore the pathogenicity and function of these SCA14-associated PRKCG mutations, HEK293T and HeLa cells were transfected with the plasmids of empty vector, wild-type PRKCG and indicated PRKCG mutants. Protein stability, aggregation propensity, phosphorylation status, mitochondrial function and cytotoxicity were then measured. We found that H101R mutant PKCγ protein is unstable, prone to aggregate, exhibits reduced basal phosphorylation, and is resistant to agonist-mediated dephosphorylation. Also, H101R mutant PKCγ protein could result in increased apoptosis and reduced cell viability. These findings are similar to other pathogenic mutations. Additionally, cellular mitochondrial dysfunction was observed for the first time in cells expressing mutant PKCγ. Together, we identified three PRKCG mutations, expanding the mutation spectrum of PRKCG in China. The c.302A > G, p.H101R variant is pathogenic and mitochondrial dysfunction is suggested involved in the pathogenesis of SCA14.