Bridging pleiotropic mechanisms in leprosy type-1 reactions and neurodegenerative diseases.

Leprosy is an infectious disease of the skin and peripheral nervous system. Sudden episodes of hyperinflammation, known as Type 1 Reactions (T1R), are a main contributor to permanent nerve damage in leprosy. The genetic component associated with the neuro-inflammatory phenotype of T1R displays pleiotropic effects with Parkinson's disease (PD). In this study, we explored the genetic overlap between PD and T1R and expanded the evaluation of pleiotropic effects between T1R and other neurodegenerative disorders. We replicated the association of PD-linked rare variants in PRKN with T1R in Vietnamese leprosy patients. Analysis of 24 PD associated-genes revealed compound effects between rare protein-altering variants and T1R in the interacting genes PRKN/PINK1 (P = 2.7; OR = 4.0) and a combination of rare/low frequency variants in the LRRK2/GAK pair (P = 6.7; OR = 0.54). These findings validated a genetic overlap between T1R and PD with two distinct axes, one of shared risk via PRKN/PINK1 and a second of antagonistic pleiotropic via LRRK2/GAK. When testing an additional 94 genes associated with neurodegenerative diseases we identified variants in the amyotrophic lateral sclerosis disease-linked gene TBK1 associated with T1R (P = 0.004; OR = 12.9). Our results highlight shared biological processes between leprosy and neurodegenerative diseases, which may indicate candidate drugs for repurposing to improve T1R management.