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Carriers of genetic marker for Alzheimer’s disease show signs of attention impairment, study finds

In a recent study, researchers investigated memory and attention in individuals carrying a genetic marker for Alzheimer’s disease.

Alzheimer’s disease (AD) is a chronic condition and the most common cause of dementia. Our knowledge of the disease has grown significantly since the first diagnosis in 1907, but effective treatments still lack. Genetic factors account for about 70% of the risk of developing AD. Among the over 20 known genetic risk factors, the Apolipoprotein (APOE) gene is the biggest risk factor for AD. This gene can appear in three different variants in the population, namely APOE2, APOE3, and APOE4. People carrying only the APOE4 variant are at higher risk of AD than those with non-APOE4 variants or with a combination of different versions of the gene. The disease usually goes unnoticed in its early stages and it may take years for the development of symptoms such as memory loss. There is therefore a need for methods to detect AD in its early stages to allow for immediate intervention. Researchers at Baycrest, Canada, in collaboration with colleagues from the University of Oxford, UK, developed a new method to study memory and attention in people carrying the genetic marker for Alzheimer’s disease APOE4. Their results are published in the journal Scientific Reports.

The study involved 60 participants of age between 40 and 61 years. The scientists divided the participants into three groups: individuals carrying the APOE4 gene, those with a combination of APOE3 and APOE4, and individuals carrying only the APOE3 variant. All individuals then participated to a listening test. Each participant listened to 92 audio clips and had to pay attention to where the sound came from. They then reported the information to the scientists, and had to repeat the test in case of incorrect answers. After a one-hour break, the participants listened to two more rounds of the audio clips. The first play-through allowed the participants to become familiar with the direction the sound was coming from, while an additional sound was added at the end of each clip during the second play-through. The researchers then asked the participants whether they could hear the additional tone, and used the data collected from the listening tests to perform a statistical analysis.

The researchers found the participants capable of learning and remembering the location the sound came from independently of the APOE version carried. However, APOE4 carriers had a harder time than the other two groups at detecting the sound added at the end of the audio clips. This finding suggests that participants with the APOE4 gene could not take advantage of recently learned information to improve their performance in the listening test. The attention deficit in APOE4 carriers also appeared to get worse as the age of participants increased. The participants in this study were healthy individuals of an average age –  over two decades younger than the age at which the first symptoms normally appear. Yet, the method developed by the researchers proved sensitive enough to detect an attention deficit in people carrying a gene that increases the risk of developing AD about 15-fold. This work might be a starting point for the development of more sensitive approaches to detect AD in its very early stages.

Written by Raffaele Camasta, PhD

References:

Zimmermann, J., Alain, C., & Butler, C. (2019). Impaired memory-guided attention in asymptomatic APOE4 carriers. Scientific Reports, 9(1), 8138.

Carriers of Alzheimer’s genetic marker have greater difficulty harnessing past knowledge. https://www.eurekalert.org/pub_releases/2019-08/bcfg-coa082119.php

Lane, C. A., Hardy, J., & Schott, J. M. (2018). Alzheimer’s disease. European Journal of Neurology, 25(1), 59–70.

Image by Karolina Grabowska from Pixabay

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