PROJECT SUMMARY / ABSTRACT Charcot-Marie-Tooth disease (CMT) is the most commonly inherited peripheral neuropathy but is still a rare disease affecting approximately 150,000 people in the United States. CMT causes distal muscle weakness and contracture, impairing the ability to walk. Progressive loss of walking ability is the most significant contributor to reduced quality of life in persons with CMT. Because disease progression is highly heterogeneous, it is difficult to predict how an individual’s gait will change over time. The long-term goal of this research is to understand the natural history of changes in ankle function during gait in youth with CMT to be able to predict disease progression for individual patients. The current project aims to 1) obtain follow-up (longitudinal) gait analysis data on patients with prior gait analysis studies and 2) identify patient and clinical characteristics, including functional gait phenotypes, that predict patterns of deterioration of gait function over time. We hypothesize that changes in walking ability can be predicted by considering functional gait phenotypes based on ankle kinematics and kinetics in addition to clinical characteristics like CMT type, sex, age, range of motion, and strength. We have previously studied the association between gait and age in CMT, but this research is limited by the use of primarily cross-sectional data. Preliminary results from a small sample of longitudinal assessments suggest that there may be patterns of change that are not captured by the cross-sectional data. This study will collect follow-up gait analysis data on patients with CMT who have had prior gait analysis studies to create a larger longitudinal data set. These longitudinal data will be used to determine whether functional gait phenotypes can improve the prediction of future walking ability in youth and young adults with CMT. Better understanding and being able to predict the changes in gait expected for individual patients is important both to improve care for individual patients and also to be able to evaluate the effects of emerging treatments in future clinical trials.