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δ Scores Identify Subsets of "Mild Cognitive Impairment" with Variable Conversion Risks
Donald R Royall1,2,3,4, Raymond F Palmer3
1Departments of Psychiatry, The University of Texas Health Science Center, San Antonio, TX, USA.
Journal of Alzheimer'S Disease : JAD
|May 26, 2019
Summary
A new dementia severity score, dDx, strongly predicts mild cognitive impairment (MCI) to Alzheimer's disease (AD) conversion. Misdiagnosis of MCI cases, particularly in minority groups, may explain disproportionate AD conversions.
Area of Science:
- Neuroscience
- Cognitive Science
- Gerontology
Background:
- The latent variable "delta" (δ) is a transdiagnostic measure of dementia severity, applicable as a composite d-score.
- Multiple validated δ homologs exist, all associated with dementia severity and mild cognitive impairment (MCI) conversion risk.
Purpose of the Study:
- To assess the impact of a novel δ homolog, dDx, on MCI conversion risk.
Main Methods:
- A new δ homolog (dDx) was developed using data from 1,230 Mexican-American (MA) and 2,215 non-Hispanic White (NHW) participants in the Texas Alzheimer's Research and Care Consortium (TARCC).
- Normal controls (NC) and MCI participants (n=1,445 and n=723, respectively) were followed annually for up to 6 years.
Main Results:
- Each standard deviation decrease in dDx score significantly increased MCI conversion risk (OR=16.39).
- Functionally salient cognitive impairment (FSCI) cases, identified below the Alzheimer's disease (AD) diagnostic threshold, showed a 73-fold increased risk of AD diagnosis.
- MCI cases identified as FSCI(+) disproportionately accounted for prospective conversions, with risk factors including younger age, absence of APOE ε4, lower education, and MA ethnicity.
Conclusions:
- A significant minority of MCI cases may be misdiagnosed as FSCI.
- These misdiagnosed MCI cases disproportionately contribute to Alzheimer's disease conversions.