October 18, 2011

Cornell Professors Predict Alzheimer’s Disease

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With one in eight older Americans suffering from Alzheimer’s disease, Prof. Charles Brainerd, human development, and Prof. Valerie Reyna, human development, are developing mathematical models that can predict whether a person is likely to develop this disease in the future. These models analyze the changes in memory over time, and attempt to diagnose the disease as early as possible, so that preventative measures can be sought.

Essentially, as people age, their memory can be classfied either as healthy aging, mild cognitive impairment or Alzheimer’s dementia. Mild cognitive impairment is considered a precursor to Alzheimer’s dementia. Over time, patients might transfer from healthy aging to mild cognitive impairment, and eventually exhibit clinical symptoms of Alzheimer’s dementia.

However, a drawback is that there is no objective measure to distinguish between mild cognitive impairment and Alzheimer’s dementia. The diagnosis of either condition relies on the psychiatrist’s discretion of the significance of the memory loss. One of the goals of Brainerd and Reyna’s research is to predict that a patient will develop mild cognitive impairment later on in their lives, with the assumption that earlier detection will lead to better treatment.

Currently, there is no known cure for Alzheimer’s dementia. However, when asked what treatment options were available to patients with mild cognitive impairment, Brainerd said, “If you study people over 70 who become classified as mildly cognitively impaired and follow them up for two years, a significant proportion will spontaneously convert back to normalcy. So, if you had interventions at that stage, you could forestall that [impairment].”

For their research, Brainerd and Reyna used data that was collected by the Aging, Demographics and Memory Study, commissioned by the National Institute of Health. The sample used was statistically determined to be nationally representative and was conducted on approximately 840 people over the age of 70, whose memory was monitored over a period of time.

Each patient went through a series of recall tests. They were given lists to memorize, and asked to repeat these later, to test the extent of their recollection.

The current analysis conducted by Brainerd and Reyna is based on data collected over 18 months. Brainerd and Reyna used this data to develop mathematical models that predicted whether a person would develop cognitive impairment.

So far, Brainerd said, “In the 18 month longitudinal study, we were able to identify people, who [initially] showed normal memory performance and who would develop impairment later.”

Recently, the ADAMS database has been updated to include five years follow-up, so Brainerd and Reyna are working on refining their models to predict the development of dementia further in advance.

Reyna said they were also working on creating an improved assessment, by separating out the different kinds of memory that were being tested. This would allow the test to monitor, more specifically, which type of memory was failing.

There are essentially two main kinds of memory –– verbatim and gist memory. Verbatim memory is used to recall details such as exact words and numbers. This memory increases from childhood to adolescence, and reaches its peak in young adults. After that, as people age, verbatim memory deteriorates over time. Gist memory, on the other hand, is used to store substance, or information collected in a lifetime, and in healthy aging, is not found to be reduced at all.

The available data also showed a correlation between the presence of a certain genetic marker, and the development of mild cognitive cognitive impairment. While there was a consistent relation between the APOE E Genotype and the disease, the allele can only be used in limited circumstances to predict the occurence of impairment.

However, Reyna explained, the mathematical models they developed uncovered the empirical signature of verbatim vs. gist memory. When the data was considered in terms of a group, these measures performed reliably, better than the genetic markers. However, the accuracy with which the models can predict individual cases has yet to be evaluated.

Until now, the relation between mild cognitive impairment and Alzheimer’s dementia has been in contention. While most people show a marked transition from mild cognitive impairment to Alzheimer’s, according to Reyna, some directly develop “what clinically presents as Alzheimer’s.” Since there is no absolute measure for the diagnoses, the distinction is sometimes vague.

Brainerd and Reyna’s models measure what is actually impaired, before symptoms can be observed. This data defines a clear link between the two conditions, and also helps to clarify why the previous studies have shown conflicting results.

When asked about the importance of these findings, Reyna said, “If you can delay cognitive impairment only for a little while, it can help not only the individual, but also society … About 10 percent [of people over the age of 70] convert every year to mild cognitive impairment.”

When asked about a means of prevention, Brainerd said, “There are brain exercise programs…one, in particular that produced significant differences in people who participated in it, and people who didn’t.”

Original Author: Rujuta Natu