Subjective cognitive decline (SCD) is gaining more recognition as a potential risk factor for developing AD. SCD appears before the onset of noticeable cognitive impairment, suggesting it could be a valuable focus group for early intervention studies. A new study, featured in JAMA Psychiatry, underscores the importance of SCD as a potential early indicator of Alzheimer’s disease and other dementias.
SCD refers to a self-perceived worsening of cognitive abilities, such as memory and thinking skills, despite normal performance on cognitive tests. It is often considered the earliest symptomatic stage of the Alzheimer’s disease continuum and can precede mild cognitive impairment (MCI) and dementia. Individuals experiencing SCD may notice subtle changes in their cognitive function before these changes become apparent to others or detectable through clinical tests.
The Framingham Heart Study, a renowned community-based prospective cohort study, assessed SCD from 2005 to 2019 with up to 12 years of follow-up. The analysis included 3,585 participants aged 60 and older who were cognitively normal at the start. The study enrolled 3,585 individuals with an average age of 68, comprising approximately 55.1% women and 91.6% non-Hispanic White participants. Among them, 50.3% were college graduates, and 21.5% carried a gene associated with AD. Each participant contributed an average of 2.1 valid visits during the study. Over the study period, 6.6% of participants developed MCI, 2.0% developed AD, and 2.5% developed dementia of any cause.
The study found that individuals with SCD were at a significantly higher risk for developing MCI, Alzheimer’s disease, and all-cause dementia. Specifically, SCD was associated with a 57% increased risk for MCI, a 198% increased risk for AD, and a 114% increased risk for all-cause dementia. On average, SCD preceded the diagnosis of MCI by 4.4 years, AD by 6.8 years, and all-cause dementia by 6.9 years, suggesting that SCD may serve as an early warning sign. The study highlighted that SCD could be an independent risk factor for cognitive decline, irrespective of the presence of the APOE ε4 gene or a high Alzheimer’s disease polygenic risk score (PRS).
Individuals reporting SCD during all visits were more frequently women and reported higher rates of depression. Rates of cognitive impairment were also elevated in this group compared to those without SCD: MCI (8.6% vs. 5.8%), AD (3.4% vs. 1.5%), and all-cause dementia (3.9% vs. 2.0%).
The study findings suggest that SCD, especially when reflecting SCD+ features, can be a crucial marker for identifying individuals at higher risk for cognitive decline. The researchers advocate for further investigation into SCD as a potential independent risk factor for AD and other dementias, beyond the genetic risks posed by APOE ε4 and AD PRS. This significant study contributes to the growing body of evidence that subjective cognitive decline is an early indicator of cognitive impairment and dementia. Recognizing and monitoring SCD in community settings could pave the way for earlier interventions and potentially slow the progression of Alzheimer’s and other dementias.
Reference
- Kang M, Li C, Mahajan A, Spat-Lemus J, Durape S, Chen J, et al. Subjective Cognitive Decline Plus and Longitudinal Assessment and Risk for Cognitive Impairment. JAMA Psychiatry [Internet]. 2024 Jul 3 [cited 2024 Jul 8]; Available from: https://doi.org/10.1001/jamapsychiatry.2024.1678
- Molinuevo JL, Rabin LA, Amariglio R, Buckley R, Dubois B, Ellis KA, et al. Implementation of subjective cognitive decline criteria in research studies. Alzheimer’s & Dementia. 2017 Mar 1;13(3):296–311.