A human gene present in 75 percent of the population is a key reason why a class of drugs for Alzheimer’s disease seemed promising in animal studies but failed in human studies.
While a previous study investigated the function of the gene in tissue culture, this is the first time that researchers have clinically shown the drugs’ effect based on a patients’ genotype.
The researchers caution that the study has its limitations and randomized double blind studies are necessary to confirm the results.
Different approaches for Alzheimer’s disease
“This research provides proof of concept that since different mechanisms are at work in Alzheimer’s in different patients, we need to develop more personalized treatments that will prove more effective in individuals,” says Kinga Szigeti, director of the Alzheimer’s Disease and Memory Disorders Center at the University at Buffalo, part of UBMD Neurology, and associate professor of neurology in the Jacobs School of Medicine and Biomedical Sciences.
The gene, CHRFAM7A, is a fusion between a gene that codes for an Alpha 7 receptor for acetylcholine, a neurotransmitter involved in memory and learning and long associated with Alzheimer’s, and a kinase, a type of enzyme.
Szigeti explains that the gene is present in two flavors, a functional gene and one that is not made into protein.
“This splits the population 1-to-3 between non-carriers and carriers,” says Szigeti. CHRFAM7A has been implicated in many neuropsychiatric disorders, such as schizophrenia and bipolar disease.
Szigeti explains that three of the four drugs now available for Alzheimer’s work by stimulating all receptors that respond to acetylcholine. More specific drugs for Alpha 7 have been in development for over 10 years but failed when moved to the clinical phase.
The human fusion gene modulates the Alpha 7 receptor, one of the receptors binding amyloid beta, the protein that is the hallmark of Alzheimer’s that disrupts neuronal communication.
“Since this human fusion gene was not present in the animal models and screening systems used to identify drugs, 75 percent of Alzheimer’s patients who do carry this gene are less likely to benefit and therefore are at a disadvantage,” she says. “This may account for the translational gap.”
With and without CHRFAM7A
“With this study, we compared the effect of cholinesterase inhibitors in patients who did or didn’t carry this gene,” says Szigeti. “People who don’t have the gene respond better to the drugs available now.”
She adds that neurons vulnerable to Alzheimer’s express Alpha 7 and that may be the reason why they die first.
“Our work confirms that Alpha 7 is a very important target for treating Alzheimer’s but the right model—a human model—has to be used when testing new drugs,” says Szigeti.
The findings suggest that a more personalized approach to each patient may be required, based on their CHRFAM7A genotype. One drug may work in 25 percent of the patients, while another will work in 75 percent.
The research used data from a ten-year, longitudinal, multicenter cohort study by the Texas Alzheimer Research and Care Consortium (TARCC) on 345 Alzheimer’s patients.
The researchers presented the work at the annual Alzheimer’s Association International Conference in Los Angeles. Additional coauthors are from the University of Texas Southwestern Medical Center, Baylor College of Medicine, and the University at Buffalo.
The Alzheimer’s Association, the Clinical and Translational Science Award pilot grant program, the Edward A. and Stephanie E. Fial Fund, the Community Foundation for Greater Buffalo, and the Dr. Louis Sklarow Memorial Trust funded the work.
Source: University at Buffalo