Somatic mutations in Parkinson disease are enriched in synaptic and neuronal processes

The role of somatic mutations in complex diseases, including neurodevelopmental and neurodegenerative disorders, is becoming increasingly clear. To explore their relevance in sporadic Parkinson disease, we performed whole-exome sequencing in blood and four brain regions of ten patients. We identified 59 candidate somatic single nucleotide variants (sSNVs) through sensitive calling and extensive filtering. We validated 27 of them with amplicon-based deep sequencing, with a 70% validation rate for the highest-confidence variants. Most of the sSNVs were exclusively called in blood but were also found in the brain tissues with the ultra-deep amplicon sequencing, demonstrating the strength of multi-tissue sampling designs. We could confirm between 0 and 6 sSNVs per patient and generally those with a shorter lifespan carried more variants. Remarkably, the validated sSNVs are enriched in genes with synaptic functions that are co-expressed with genes previously associated with Parkinson disease.