# Gene expression asymmetry in Parkinson’s disease: variation of CCT gene expression is correlated with hemisphere specific severity

## TL;DR

This study found that gene expression differences in the brain hemispheres of Parkinson’s disease patients correlate with symptom severity and may indicate a protective role for the CCT gene.

## Contribution

The study identifies CCT gene expression asymmetry as a novel correlate of Parkinson’s disease hemisphere-specific severity.

## Key findings

- Hemispheric gene expression variation in PD brains correlates with symptom onset side.
- CCT gene levels are decreased in neurons with α-synuclein inclusions in a mouse model of PD.
- Stratifying PD brains by gene expression reveals genetic asymmetry patterns.

## Abstract

Parkinson’s disease (PD) symptom onset is typically unilateral, which may be related to molecular differences underlying hemispheric vulnerability. Here we sampled prefrontal cortex bilaterally from people with PD and healthy controls and performed RNA-seq on neuronal nuclei to determine hemispheric and disease-related differences. Brain hemispheres were categorized based on whether they corresponded to the side of symptom onset (severe) or the opposite side (moderate) and compared for differences in gene expression. We employed two a priori approaches; first we identified genes differentially expressed between PD and controls and between PD brain hemispheres. Second, we examined the presence of, and correlates to, variations in the asymmetry for some differentially expressed genes. We found large variation among individuals with PD, and so PD stratification by gene expression signature was required for patterns of genetic asymmetry to emerge. For a subset of PD brains, hemispherical variation of CCT gene levels correlated with the side of PD symptom onset. In a mouse model of PD, neurons with α-synuclein inclusions had decreased Cct expression. These results suggest that CCT expression plays a protective role in PD.