After five years of researching genetics among different ethnic groups, Boston University researchers, along with researchers from Columbia University and the University of Toronto, said they are one step closer to understanding the code to late-onset Alzheimer’s disease, which affects 4.5 million Americans today.

Published Jan. 14 in Nature Genetics, the study identifies the gene, named sortilin-related receptor (SORL1), as a major player in the development of Alzheimer’s in individuals 65 years and older. Because the SORL1 gene has 500 variants — any of which could be responsible for Alzheimer’s — the discovery is only the beginning of the challenge to understanding the disease completely, said School of Public Health professor Dr. L. Adrienne Cupples.

“There is still a long way to go, but if we can understand the effects of this gene, then we may be able to enhance or block its action through the development of new therapies,” she said.

Instead of finding an immediate treatment, School of Medicine professor Dr. Lindsay Farrer said the discovery of SORL1 “identifies a new pathway for understanding the biology of the gene” and provides scientists, including Columbia researcher Dr. Richard Mayeux and Toronto researcher Dr. Peter St. George-Hyslop with “an opportunity to regulate the regulator” in potential Alzheimer’s therapy.

Dr. Ekaterina Rogaeva, another Toronto team researcher, said the journey to an Alzheimer’s cure is a long one – and will take at least two to three years to identify the variants and at least another 10 years before the drug can be approved and available for use.

The study, which receives funding from a variety of institutions including the Alzheimer’s Association of the United States and the Canadian Institute of Health Research, began in 2002. The three universities collaborated to examine 6,000 volunteers from four ethnic groups: whites, blacks, Caribbean-Hispanics and Israeli-Arabs. Rogaeva said the study’s ethnic variety is necessary because certain genes affect ethnic groups differently. Some previous studies suggested the gene’s effect in blacks is weak in comparison to other ethnic groups, according to a Jan. 14 BU press release.

Farrer said researchers have confidence in the SORL1 gene discovery because of its prevalence in all four ethnic groups.

“[The study] is clearly illustrating the importance [of representing a variety of ethnicities] both from a scientific standpoint and from a clinical health standpoint . . . the findings are more robust when we can show . . . different ethnic groups,” he said.

As the research work continues, Farrer said he would like to enhance the quality of the research by making it a more collaborative effort within the university.

“Within the Medical Campus, it’s already a multi-departmental enterprise,” he said. “Now, as the nature of the research based on this discovery becomes multi-disciplined, we are trying to extend our collaboration to departments on the Charles River Campus. It’s a natural thing to do.”

Researchers discovered the first gene linked to Alzheimer’s, apolipoprotein E (APOE), in 1993. The variant of the gene, called e4, is responsible for an increased number of amyloid plaques, clumps of protein found in the brain tissue of those affected by Alzheimer’s, according to a U.S. National Library of Service website.

According to the press release, variants of SORL1, which are more commonly found in Alzheimer’s victims than in their healthy peers, distort the normal behavior of SORL1. In healthy adults, the gene sends the amyloid precursor protein (APP) down a brain pathway so that it can be recycled. When affected by its variants, SORL1 misguides the APP by sending it down another route that increases the toxic production of the amyloid beta peptide, leading to Alzheimer’s.

“I’d like to say [we could identify these variants] tomorrow, but the variants that we’re looking for are not going to be obvious,” Farrer said. “They’re not associated with amino acids, so [they’re] not involved with structure.”