The discovery of an enzyme biomarker that distinguishes even early Alzheimer’s disease from other dementias may allow physicians to reach accurate diagnoses easily with use of a simple skin test, according to an article published online by the Proceedings of the National Academy of Sciences.

The current research showed that the test can accurately distinguish between Alzheimer’s disease and other forms of dementia during the first one to two years of the disease’s progression. The biomarker showed high accuracy when tested with human fibroblasts from a tissue bank, as well as for samples obtained in a previous, unpublished study of patients with autopsy-confirmed diagnoses. The biomarker could also potentially be used with blood samples.

“When it begins, Alzheimer's disease is often difficult to distinguish from other dementias or mild cognitive impairment,” says Daniel L. Alkon, MD, scientific director of BRNI and coauthor of the study with Tapan K. Khan, PhD, assistant professor. “Potential treatments of Alzheimer’s, however, are likely to have their greatest efficacy before the devastating and widespread impairment of brain function that inevitably develops after four or more years.”

Many scientists have concluded in recent years that Alzheimer’s effects are found throughout the body, not just in the brain. By testing for signs of Alzheimer’s-related inflammation in fibroblasts, the team located a biomarker for the disease that can be tested without the invasive tests previously required.

Alzheimer’s disease stimulates a change in the enzyme MAP Kinase Erk 1/2. When fibroblasts are tested by exposing them to bradykinin, a common inflammatory signal, the Erk 1/2 response in skin cells of Alzheimer’s patients was sharply distinguished from the results in cells from age-matched controls. It was also differentiated from the skin cells from patients with non-Alzheimer’s dementias, such as Parkinson's disease, multiple infarct dementia and Huntington's chorea.

Drs. Khan and Alkon have created an Alzheimer’s Index that may contribute greatly to physicians’ evaluations of patients with dementia. The index is a mathematical formula that allows the scientists to convert the test results for each patient to a single number.

“The results demonstrate that when the Alzheimer’s Index agrees with the clinical diagnosis of the presence of Alzheimer’s, there is a high probability of accurate diagnosis,” Alkon said.