Biomarkers predict cognitive impairment risk
medwireNews: US researchers have used population-based data to predict an individual’s absolute risk of developing cognitive impairment according to imaging-based biomarkers of amyloid (A) and neuronal injury (N).
Ronald Petersen (Mayo Clinic, Rochester, Minnesota) and colleagues found that risk increased with age and any biomarker abnormality, and was higher in men and people with a high school education relative to women and those with some college education, respectively.
The findings are based on data for 763 participants of the Mayo Clinic Study of Aging who were aged 70 years or older and cognitively unimpaired at baseline.
Of these, 26% were A–N–, meaning they had a negative amyloid positron emission tomography result as well as no evidence of neuronal injury by structural magnetic resonance imaging, 15% were A+N−, 30% were A−N+ and 28% were A+N+.
During a median 4 years of follow-up, 152 (19.9%) individuals progressed to mild cognitive impairment (MCI) and seven (0.9%) developed dementia.
The incidence of progression to MCI or dementia at age 75 and 85 years was 2.4 and 6.5 events per 100 person–years, respectively.
When stratified according to biomarker status, the progression rates, averaged for 75-year-old men and women with some college education, were 3.9 events per 100 person–years in the A+N+ group, 1.1 events per 100 person–years in the A−N− group and 2.3 events per 100 person–years among individuals who were either A+N− or A−N+.
By 85 years of age, the rates had increased to 8.9, 2.6 and 5.2 events per 100 person–years, respectively.
The researchers also created a grid giving the likelihood of an individual developing MCI or dementia within 5 or 10 years according to age, sex, education level and biomarker status.
As an example, they estimate that a 75-year-old man with some college education and abnormal amyloid and cortical thinning biomarkers (A+N+) has a 23% chance of cognitive impairment by age 80 years. With just one positive biomarker (either A or N) the risk is 14–15%, and with normal biomarkers (A–N–) the chance is just 7%.
For women, the corresponding risks are 19%, 12% and 6%.
The researchers note that previous studies have found conflicting results regarding the importance of an A–N+ biomarker status, with some reporting a similar risk of progression to MCI as A–N– and others finding an increased risk.
However, based on their findings and the fact that “brain atrophy on MRI is a well-established risk factor for cognitive impairment”, Petersen and team believe it is “likely that neurodegeneration in the absence of amyloidosis is an important risk factor for MCI.”
Writing in the Annals of Neurology, the authors say their “absolute risk estimates may be useful to clinicians in counseling patients with respect to the role of [Alzheimer’s disease] biomarkers”.
They conclude: “Our results provide easily interpretable estimates of the chance of becoming cognitively impaired in 5- and 10-year windows stratified by biomarker group.”
By Laura Cowen
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