The purpose of this study is to investigate whether speed-dependent measures of gait (so called gait signatures) can be identified in patients with neurological conditions that affect gait, particularly in subjects with parkinsonian disorders.

This study aims to determine whether the gait patterns, modeled as gait signatures, in these subjects differ in predictable and quantifiable ways from those of age- and sex-matched healthy controls (cross sectional data). This will be conducted by asking 40 Parkinsonian disorder subjects and 40 age-matched healthy control subjects to walk 9 trials over an 18 ft walkway embedded with pressure sensors at baseline, self-selected slower and faster speeds. In addition, the protocol aims to investigate whether clusters of gait patterns can be identified within subgroups of individuals with parkinsonian disorders with varying co-morbidities or treatment conditions as well as patients with ataxia or huntington's disease. For this aim an additional 20 Parkinsonian disorder subjects need to be recruited. Patients with parkinsonism as defined by UK PD Brain Bank Criteria (n=60), subjects with acquired or inherited ataxic syndromes (n=10), age- and sex matched controls (n=40) and young healthy controls (n=30) will be recruited. The cohort of young healthy controls serves to validate gait analysis modeling.There is an optional second visit in the protocol during which approximately 20 subjects with Parkinsonian disorders, who are willing to come off antiparkinson medication and if applicable, off both medication and deep brain stimulation, are asked to walk an additional 9 trials. The PD and older healthy control subjects have to option to be followed longitudinally.

Inclusion Criteria:

• Age 18-85 (for both healthy and affected subjects).
• Presence of at least 2 of the following: bradykinesia, rest tremor, rigidity, postural instability (UK PD Brain Bank Criteria) (Affected subjects only).
• Montreal Cognitive Assessment will be employed to determine whether subjects will need the assent of a legally authorized representative. Subjects with MOCA ≤ 21 will be consented only with the assent of the subject and informed consent of the authorized legal representative (Affected subjects only).
• These may include subjects who may have indeterminate parkinsonism, when it is not clear whether they have idiopathic Parkinson's Disease versus one of the Atypical Parkinsonisms, such as Vascular Parkinsonism, Multiple System Atrophy, Progressive Supranuclear Palsy, Normal Pressure Hydrocephalus or Corticobasal Degeneration (Affected subjects only).
• Subjects with assistive devices will be eligible for the study and may use them during the study (Affected subjects only).
• Absence of complaints regarding difficulty walking such as arthritic pain, fatigue during walking or slowness of walking (Healthy subjects only).

Exclusion Criteria:

• Presence of alternative explanation for parkinsonism such as head trauma, drug-induced parkinsonism (affected subjects only).
• Currently being treated for major medical illness requiring recent hospitalization (<14 days) (for both healthy and affected subjects).
• Currently participating in another clinical study with an intervention arm (for both healthy and affected subjects).
• Inability to consent due to cognitive impairment and absence of legally authorized representative (for both healthy and affected subjects).
• Subjects with any cardiac, pulmonary conditions (congestive heart failure requiring hospitalization within the past 90 days, recent myocardial infarction < 90 days, supplemental oxygen-requiring subjects due to cardiac or pulmonary conditions) that limit their ability to safely participate in a walking trial (for both healthy and affected subjects).

Subjects with Parkinsonism as defined by UK PD Brain Bank Criteria. The study population includes subjects with Parkinson's Disease and may also include subjects who may have indeterminate parkinsonism, when it is not clear whether they have idiopathic Parkinson's Disease versus one of the Atypical Parkinsonisms, such as Vascular Parkinsonism, Multiple System Atrophy, Progressive Supranuclear Palsy, Normal Pressure Hydrocephalus or Corticobasal Degeneration. Subgroups include subjects with ataxia and huntington's disease and control subjects without known neurological disease.