The primary objective of this study is to discover blood-based biomarker of brain Huntingtin (HTT) protein using extracellular vesicles to be used in evaluating target engagement in HTT lowering clinical trials. Secondary objectives of this study include developing more accurate biomarkers of Huntington disease (HD) progression or conversion and to develop standard practices for extracellular vesicle biomarker discovery research. The investigators hypothesize that brain-derived extracellular vesicles (EVs) isolated from human biofluids contain biological cargo specific to their tissue of origin that could allow their use as brain biomarkers for HD. EVs are lipid bilayer-delimited particles that are naturally released from cells in the brain. The investigators will investigate if EVs contents reflect the pathological alterations occurring with disease progression when compared with EVs isolated from biofluids of healthy non-HD persons.