According to a new study, it is perhaps in the eye that the presence of Alzheimer’s disease will be detected tomorrow.
Alzheimer’s disease begins to change and damage the brain years, even decades, before symptoms appear. Identifying the risk of Alzheimer’s disease is therefore essential to slow its progression. A news studypublished online in the September 9, 2019 issue, Neurobiology of Aging, describes an innovative, inexpensive and non-invasive method. Scientists at the California School of Medicine in San Diego say that measuring the speed of a pupil’s dilation during cognitive tests can help screen individuals at increased genetic risk for Alzheimer’s disease before cognitive decline does not begin.
With the aging of the population, doctors are faced with pathologies that are still complex. Alzheimer’s disease is at the top of the list. This form of dementia causes progressive cognitive decline, particularly in memory. Those affected gradually lose their independence and usually require medical assistance. According to the FRM (Medical Research Foundation), 900,000 French people suffer from this debilitating disease in 2019. This figure is growing alarmingly and should reach more than two million in 2040. It is the leading cause of heavy dependency in the elderly and the leading cause of entering an institution (Alzheimer’s and related diseases).
Tau proteins develop in the locus coeruleus
The diagnosis is not simple and requires a complete analysis of the medical history of the patients as well as a detailed observation of their brain. In recent years, researchers who have studied the pathology of Alzheimer’s disease have primarily focused their attention on two factors: the buildup of protein plaques in the brain called beta-amyloid and another protein called tau. Both have been associated with the destruction of neurons, leading to progressive cognitive dysfunction.
This new research is based on the observation that tau proteins tend to grow initially and damage a region of the brain called the locus coeruleus (LC). Previous research had shown that LC largely induced responses to pupillary dilation. It therefore aimed to determine whether early accumulations of tau in the LC could modify pupil dilation in such a way as to allow the identification of pre-symptomatic Alzheimer’s disease.
A previously published study by the current research team demonstrated that adults with mild cognitive impairment had greater pupil dilation on a cognitive test, compared to a healthy adult. Importantly, these differences in pupil dilation emerged even when the two groups scored the same on cognitive tests.
The results therefore confirmed an association between pupillary responses during cognitive tasks and genetic risk scores for Alzheimer’s disease, despite the fact that all subjects still had normal cognition.
Proof that pupil measurement is effective
“Given the evidence linking LC, tau, and the association between pupillary response and polygenic risk scores for Alzheimer’s disease, these results are strong evidence that measuring pupillary response is effective. Cognitive tasks could be another screening tool to detect Alzheimer’s disease before the onset of symptoms,” says Willam Kremen, first author of this new study, who admits that this test is still in concept stage and more work is needed to verify these results.
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