Motor speech and non-motor language endophenotypes of Parkinson's disease.

Introduction: Idiopathic Parkinson's Disease (PD) results in a range of motor and non-motor impairments. Clinical diagnosis commonly occurs after substantial neurophysiological damage limiting the opportunity for neuroprotective treatments. Uncovering sensitive objective markers with the capacity to detect pre-symptomatic disease and track disease progression is therefore a priority. Speech may provide an ideal proxy marker for PD; a quantifiable biometric that displays salient changes in early disease and appears to evolve with disease progression.Areas covered: This review describes the endophenotype of speech, voice, cognition and language modalities in PD and investigates the speech as a 'proxy marker' of PD disease state.Expert opinion: Detailed characterization at different disease stages are needed and must incorporate longitudinal assessment to capture small but significant changes in speech, voice, cognition and language modalities within patient changes over time. Advances in technology are leading to new opportunities for acquiring data remotely and more frequently, offering more ecologically valid testing environments. Combined with automated signal processing and analysis, symptoms may also be tracked in-home readily. Features extracted may provide a 'proxy marker' for early identification of PD and objective monitoring of disease progression.