Large twin study on Alzheimer's, Inheritance and environment
The largest sample research project to evaluate the genetic and environmental influences of Alzheimer's disease has found a strong genetic basis for the disease. 11,884 twins from the Swedish Twin Registry aged 65 years and over were screened for cognitive dysfunction (Cognitive meaning mental activity such as thinking, attention, reasoning, decision making and dealing with concepts).
Of the nearly 12000 twins there were 392 pairs in which 1 or both of them had Alzheimer's disease. All the twins with suspected dementia were given additional diagnostic tests.
The research findings showed high heritability for Alzheimer disease,"58% in the full model and 79% in the best-fitting model, with the balance of variation explained by nonshared environmental influence". In other words, Alzheimer's appears to be triggered by a number of factors but a person's genetic make-up is the strongest risk factor. The study found no differences for men and women in their susceptability to Alzheimer's or their heritability to it.
Scientists often use twins to try to determine whether genetic or environmental factors influence disease risk. All the types of twins were studied, monozygotic (one egg where twins share all their genes i.e. identical twins), dizygotic (two eggs fertilized at one time who usually share about 50% genetic material).
What the Alzheimer's twin study means for you
Although this research does indicate that genes are more significant than environment in your risk factors for Alzheimer's it does not mean you will get Alzheimer's because a close family member has it. It just means that in this research there was a significant genetic link. We know that the biggest risk factor for Alzheimer's is age. In this study all the participants were over 65 years of age!
At 65 to 70 years your risk is about 1.5%
At 70 to 74 years your risk is about 3.5%
At 75 to 79 years your risk is about 6.8%
Your risk of Alzheimer's nearly doubles every 5 years so by the age of 95 nearly one half will have Alzheimer's disease.
Article Source: Role of Genes and Environments for Explaining Alzheimer Disease Margaret Gatz, PhD; Chandra A. Reynolds, PhD; Laura Fratiglioni, MD, PhD; Boo Johansson, PhD; James A. Mortimer, PhD; Stig Berg, PhD; Amy Fiske, PhD; Nancy L. Pedersen, PhD. Arch Gen Psychiatry. 2006;63:168-174. 02/15/2006
