Genetic Risk or Not?

Most reports say that children of LBD patients do not have a clear genetic risk for the disease.
But the children of Alzheimer's patients do have a risk factor.
"Q & A: Late-onset Alzheimer's" in USA Today, 2/14/06, reports that a study of twins shows a definite genetic risk for this illness.
"...genetic factors accounted for 58% to 79% of the risk of developing late-onset Alzheimer's."
Factors such as lifestyle and other diseases made up the rest of the risk.
"According to the Alzheimer's Association, the risk is two or three times higher than for someone who does not have a family history of the disease." http://www.alz.org
Dr. Margaret Gatz of the University of Southern California is interviewed by the USA Today reporter, following a study published in February in Archives of General Psychiatry.
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In Time Magazine's special issue "The Year in Medicine from A to Z" (Dec. 5, 2005), a short notice on Alzheimer's lists one of the factors that can cause the disease:
"...inflammation caused by lost or loose teeth, and the resulting infection, can quadruple the risk of developing Alzheimer's. Treating those inflammatory episodes could help stave off the disease" p. 63.
Mom replaced the teeth in her upper jaw and four teeth in her lower jaw when she was in her early forties. I wonder if there was infection present and whether it affected her brain.