This is a longitudinal open-ended observational study. Participants will attend two annual study visits, an Annual Screening Visit followed by an Annual Sampling Visit, and may also attend an optional visit during the first year of enrollment, an Optional Repeat Sampling Visit.
During the Annual Screening Visit, medical history, and clinical and phenotypic data will be obtained. Participants who meet the eligibility requirements of the study and are willing to continue in the study, will return for an Annual Sampling Visit. During that visit, biosamples will be collected following a fast of at least 6 hours, or overnight: blood will be obtained via venipuncture and CSF will be obtained via lumbar puncture. Some participants may be invited to return for an Optional Repeat Sampling Visit approximately 4-8 weeks after the Annual Sampling Visit during their first year of enrolment.
The annual visits are at regular intervals after the first Annual Screening Visit (i.e. at 1, 2, 3 years and so on) ± 2 months. Participants will be encouraged to complete all annual visits; however, they are under no obligation to take part and will be able to skip annual visit without being discontinued from the study. Participants who do not come for an Annual Sampling Visit for three consecutive years will be discontinued from the study, but they may enrol again at a later date, if they so consent. Participants who have already completed HDClarity Sampling Visits under earlier versions of this protocol may also participate in the longitudinal study if they meet the eligibility criteria.
