Since 2005, Alzheimer’s Disease Research Centers (ADRCs) have been contributing data to the Uniform Data Set (UDS), using a prospective, standardized, and longitudinal clinical evaluation of the participants in the National Institute on Aging’s ADRC Program. The UDS consists of rich multi-domain neurocognitive, clinical, and phenotypic data, and robust criteria-based diagnoses that are considered gold-standard by the field. Participants attend annual visits to monitor their health and cognitive state, and this longitudinal data collection allows researchers to track disease progression over the years. 

The National Alzheimer’s Coordinating Center (NACC) UDS comprises the bulk of the data currently collected at NACC from all clinical core participants across all the ADRCs. Clinical core enrollees are each assigned a unique NACCID within the NACC database. 

Together with our 36 ADRCs, we have compiled data on more than 54,000 participants, each with up to 20 annual visits, and are actively following more than 20,000 participants. This includes participants who are cognitively normal and those with mild cognitive impairment or dementia symptoms, with a range of pure and mixed etiologies. 

NACC also houses a large quantity of standardized neuropathology data, with nearly 60% of deceased participants serving as brain donors. The UDS includes over 200,000 clinical assessments and has been used in over 1,500 published studies. NACC has worked successfully to streamline access to the NACC data by providing full data files that are available as "Quick Access" files.

NACC data is available on the NACC Data Platform and available to researchers everywhere through the Data Front Door (DFD), which is designed to make ADRC data as findable, accessible, interoperable, and reusable (FAIR) as possible. It is scalable to new data streams, interoperable with other data repositories, and provides secure sandbox options for collaborative data analysis to support AI-driven discovery.

The UDS Study Population

• The UDS reflects the total enrollment of the ADRC Program since 2005 and includes participants with cognitive status ranging from no cognitive impairment to dementia.
• Each Center enrolls its participants according to its own protocol — clinician referral, self-referral by participants or family members, active recruitment in community organizations, etc. Most Centers also enroll volunteers with normal cognition, and these participants tend to be highly educated.
• NACC participants are not a statistically based sample of the U.S. population — with or without dementia. Rather, they are best regarded as a referral-based or volunteer case series. Therefore, NACC data do not lend themselves to estimates of the prevalence or incidence of dementia subtypes in the general U.S. population.
• Some ADRCs require that participants agree to autopsy before being accepted for UDS participation; this may impose further selection pressures on the makeup of the NACC sample.
• ADRCs collect written informed consent from all participants and co-participants.

How UDS Data Are Collected

• The UDS data are collected using a standardized protocol for all participants enrolled in ADRC clinical cores. Data are recorded directly on UDS forms (hard copy or electronic) during the evaluation process, by clinicians or clinical staff and then processed by ADRC data cores before submission to NACC.
• Information is collected during in-person UDS related office visits, home visits, and video/telephone calls. In addition, Milestone Forms are used to document participant change in residence and living situation as well as reported death or decline to participate or administrative discontinuation by the ADRC.
• The UDS is longitudinal, and its protocol requires annual follow-up (within a +/- 6-month window) for as long as the participant is able and willing to be involved. Visit dates are important and used to calculate protocol compliance, beginning with the date of the first visit. Late-stage participants forced to drop out due to health may continue to be followed strictly for autopsy purposes (as noted on the Milestone form) where no further UDS visit is expected, without loss of protocol.
• Data are collected by trained clinicians and clinic personnel from direct observation and/or examination of participants and their co-participants (usually a close friend or family member).
• Depending on a given ADRC’s practice, assigned UDS diagnosis is made by either a consensus panel or a single physician (usually the clinician who conducted the neurological examination).
• Although the focus of the ADRCs is generally Alzheimer’s disease (AD), each ADRC also enrolls persons with other neurologic conditions or with no neurological or cognitive issues at all. This is done consistent with the individual theme of each ADRC and is consistent with the understanding of Alzheimer’s disease and related dementias (AD/ADRD) as well as the current understanding that single etiology dementias rarely occur and it is much more common to individuals to have co-existent combinations of AD, Lewy Body Disease (LBD), vascular disease, TDP-43 and other factors.

Modules

The UDS has three condition-specific modules. These are voluntarily completed by ADRCs, to document specific diseases or syndromes. The modules are completed at the choice of the ADRC, usually when the result of the main UDS indicates an additional predominant diagnosis or syndrome. Module data are held separately but linked by NACCID to UDS and other data captured by NACC.

• The Frontotemporal Lobar Degeneration (FTLD) Module has been collected since 2012 and is available to researchers via the NACC Quick-Access File. The Module is aimed at evaluating those suffering from or at risk for any of the forms of frontotemporal lobar degeneration and includes controls. To receive the FTLD Module data in the NACC Quick-Access file, submit a data request.
• The Lewy Body Disease (LBD) Module has been collected since 2017 and is available to researchers via the NACC Quick-Access File. The shortened version of the LBD Module (v3.1) was implemented in 2020. The Module evaluates those with clinically determined Lewy Body syndrome and includes controls. To receive the LBD Module data in the NACC Quick-Access file, submit a data request.
• The Down Syndrome Module was implemented in 2020 and was designed to be used with a subset of UDS participants; specifically, adults with Down syndrome. Due to trisomy 21, adults with Down syndrome have an increased risk for early onset of Alzheimer’s disease. Centers have begun collecting data which will be made available via the NACC Quick-Access File within the next year.

Stand-alone Forms

• The COVID Impact Survey F2/F3 v2 aims to collect valuable information about COVID vaccinations, infections, and hospitalizations of the UDS participants. Collecting this valuable data will be important in understanding the impact of COVID in the AD community. These forms can be administered outside of a UDS visit but can be linked to UDS data via NACCID. The data from version 1 of the forms is only distributed upon special request; all data, including version 2 form data, will be included as part of the NACC Quick-Access file within the next year.
• The Linguistic History Form (CLS) is used to collect additional information on UDS participants who indicate they are of Hispanic/Latino ethnicity on the UDS demographics form. It can be administered any time and is linked to UDS data. The data is only distributed upon special request and is not currently part of the NACC Quick-Access file.
   

Minimum Data Set (MDS)

Beginning in 1984 and ending with the 2005 implementation of the UDS, brief, single-record descriptions of ADRC participants were collected retrospectively to form the Minimum Data Set (MDS). They were abstracted from ADRC enrollment records, primarily by data managers, research assistants, and others at each ADRC. The MDS data are cross-sectional and were not originally recorded following a standard protocol. They were merely abstracted from ADRC records which primarily followed local definitions. Because of the lack of detailed, longitudinal, and standardized clinical data in the MDS, the utility of the MDS for research is limited, and combining the clinical data in the MDS with the UDS is generally not recommended. For this reason, it is not currently part of the NACC Quick-Access file but is available upon special request.