Researchers find genetic influences on memory performance in familial AD
Genetics may influence memory performance in families with a history of Alzheimer’s Disease according to researchers writing in the February 10, 2004 issue of Neurology. Previous human genetic studies focusing on memory have been limited primarily to twin studies. In this new study, NIA-supported grantees at Columbia University, Joseph Lee, DrPH, and Richard Mayeux, MD, MSc, examined the heritability of cognitive elements, including memory, in patients with AD and their family members across multiple generations. Their study included data from 1,036 individuals from 266 Caribbean Hispanic families from the Dominican Republic and Puerto Rico.
Neuropsychological tests were given to all family members and those with AD, in Spanish. Study participants were tested for memory, attention, abstract reasoning, language, and visual-spatial ability.
Researchers found that nearly 50 percent of assorted memory abilities among study participants were due to genetics, while the other half can be attributed to outside factors, such as education. Because traits, such as the genetic mutation that triggers early-onset AD, are dominant, memory performance may have an even higher genetic influence than the test results suggest.
Areas of mental ability that appear to be less influenced by genetics included attention, abstract reasoning, language, and visual-spatial ability. Even after the scores of those participants with AD were removed from analysis, researchers arrived at the same conclusions regarding memory performance. When adjustments for sex, age, education, and general intelligence were made, heritability approximations increased for cognitive tests, especially for those observed for memory. No other cognitive ability was estimated to be as closely linked to genetics as memory.
The relationship between the apolipoprotein E gene (APOE) and the risk of developing AD was tested. The g4 variant allele of APOE is strongly associated with AD. The APOE gene, however, appeared to have little influence on memory scores. When researchers controlled for the APOE gene, heritability estimates changed modestly with a slight increase in delayed recall; however, estimates made little to no changes for other memory scores.
More research is needed to establish whether these findings apply to families without multiple family members with AD and those living in the U.S. Because those who lived in the Dominican Republic received limited education between the years 1930 to 1961, the average education of those researched from this area is 6 years. Past research suggests that this group may be more susceptible to AD than those educated in the U.S., because education appears to have AD protective effects. A better grasp of which genetic influences affect memory and memory impairment in AD may shed light on which genetic factors cause this degenerative disease.