Margaret Gatz, professor of psychology, gerontology and preventive medicine, is lead researcher of an ongoing study on dementia in Swedish twins that last year revealed a genetic cause in up to 80 percent of Alzheimer’s disease cases.
Gatz, who chairs the psychology department in USC College, discussed her methodology and updated findings with a group of about 75 students, faculty and staff from across the campus at the USC Davis School of Gerontology’s first multidisciplinary research colloquium of the fall semester on Sept. 6.
Sweden, Gatz explained, possesses the largest comprehensive twin registry in the world, making her team’s examination the largest twin study ever undertaken, with close to 12,000 pairs.
Gatz offered three distinct reasons why twins, often raised in similar environments and sharing genetic makeup, are the ideal population group to study dementia.
First, they possess a relative similarity of genetic and environmental influences. Second, risk factors can be measured when comparing demented twins to their non-demented twin partners. Third, twin partners of probands, or the first affected family member who seeks medical attention for a genetic disorder, can be compared to the normal population.
All study participants were screened for cognitive dysfunction. Suspected cases of dementia received complete, in-home evaluations by a doctor and nurse.
“Sweden is about the size of California with the population of Los Angeles,” Gatz said. “Our nurses told stories of taking small boats to remote islands in order to get a diagnosis.”
Gatz found a 45 percent concordance rate for identical male pairs, demonstrating that identical twins sharing the same genetic makeup vary in their susceptibility to Alzheimer’s. In other words, if one sibling has dementia, the chances are less than half that the other twin will develop the disease.
Still, Alzheimer’s disease risk is strongly influenced by genetics. The audience was surprised by Gatz's assertion that environmental factors did little or nothing to prevent or slow the onset of Alzheimer’s disease in those born with the genetic allele ApoE-4, found in approximately 40 to 65 percent of Alzheimer’s patients.
The presence of ApoE-4, however, is not necessarily the sole determinant of the disease. At least a third of Alzheimer’s patients are ApoE-4 negative and some who possess the ApoE-4 allele never develop the disease.
For those who do not show a genetic predisposition, Gatz found a number of environmental factors that correlate to lower levels of dementia.
“Despite the fact that we found the odds of developing dementia are two times greater for those with less education than those with higher levels of education, we still think childhood illnesses, nutrition and natal environments could be the underlying risk factors,” Gatz said.
Gatz discussed other protective characteristics related to lifestyle, most notably that twins involved in complex work, or occupations with a high level of associations with people, are at lower risk of dementia and Alzheimer's disease, even when controlled for age, gender and level of education.
Gatz referred to research by USC professors Caleb Finch and Eileen Crimmins in her presentation. Her findings reinforced their assertion that environmental influences causing high inflammation early in life can adversely affect the immune system and may increase the likelihood of dementia in older adulthood.
Afterward, Finch, University Professor and holder of the ARCO/William F. Kieschnick Chair in the Neurobiology of Aging, praised her lecture as “a brilliant analysis that shows her collegiality.”
Crimmins, holder of the Edna M. Jones Chair in Gerontology, professor of sociology and associate dean of the USC Davis School, also offered acclaim for Gatz’s work.
“Margie’s work using twins to separate the effects of genes and environments is novel and deserves much praise. She is one of our most valued colleagues.”