Reference SVA insertion polymorphisms are associated with dopaminergic degeneration in Parkinson’s Disease and differential gene expression in the PPMI cohort

Abstract

Background: The development of Parkinson’s disease (PD) involves a complex interaction of genetic and environmental factors. The majority of studies investigating the genetic component of complex diseases, including PD, have focused on single nucleotide polymorphisms as this enables genome wide analysis of a large number of samples. Genome wide association studies have been crucial in identifying PD risk variants, however a large proportion of the heritability of PD remains to be identified. To investigate the component of PD that may involve complex genetic variants we characterised SINE-VNTR-Alus (SVAs), a retrotransposon known to affect gene expression, in the Parkinson’s Progression Markers Initiative (PPMI) cohort.Results: Utilising whole genome sequencing from the PPMI cohort that consisted of 179 healthy controls, 371 individuals with PD and 58 individuals classified as SWEDD (scans without evidence of dopaminergic deficit) we genotyped SVAs in the reference genome for their presence or absence identifying 81 such SVAs. Seven of these SVAs were associated with progression of the disease, including four whose specific genotypes were linked to an increase in the gradient of dopaminergic loss when comparing the caudate to putamen from DaTscan imaging analysis. These seven SVAs also demonstrated regulatory properties as they were associated with differential gene expression in whole blood RNA sequencing data.Conclusion: This study highlights the importance of addressing variation of SVAs and potentially other types of retrotransposons in PD genetics, furthermore these SVA elements should be considered as regulatory domains that could play a role in disease progression.