Olivocerebellar circuit development as a substrate for dystonia pathogenesis

Despite the progress in identifying genetic and molecular contributors to dystonia, the synaptic and circuit mechanisms that disrupt motor maturation and serve as the substrate for disease pathogenesis are only beginning to emerge. In this chapter, we highlight evidence implicating the olivocerebellar node as a key site of pathogenesis in the dystonia network. As an example of aberrant olivocerebellar circuit activity leading to dystonia, here we examine a mouse model in which excitatory neurotransmission is silenced at inferior olive to cerebellum synapses upon Vglut2 mediated conditional complex spike knockout (CSKO mice). In this model, dystonic postures emerge postnatally in a time-locked manner coinciding with disrupted olivocerebellar circuit refinement. These mice fail to undergo typical transitions from rudimentary to coordinated motor behaviors, implicating cerebellar activity as a critical driver of motor maturation, which we link to clinical observations from human patients. Anatomical and physiological evidence suggests that loss of climbing fiber signaling impairs Purkinje cell and cerebellar nuclei development, disrupting cerebellar output. We propose that a subset of dystonia etiologies, conceptually, reflect perpetual immaturity of motor commands due to these cerebellar circuit deficits, potentially identifying critical periods to restore proper motor function. Formulating dystonia as an immature motor state raises the intriguing perspective that broader etiologies of dystonia (both cerebellar and otherwise) may in part reflect a reversion of the developed motor network, similar to how strokes and neurodegenerative diseases "uncover" primitive reflexes. As a result, the CSKO mouse model provides a framework for understanding diverse etiologies of dystonia and highlights cerebellar output as a promising therapeutic target across developmental and acquired forms.