Heritability of Alzheimer's

1. Provide an estimate of h squared for the disorder. Based on this, discuss how much influence selection could have on this trait.
In a study, Heritability for Alzheimer's disease: the study of dementia in Swedish twins done in March of 1997, they wanted to find all cases of dementia in an established twin registry and to see what the heritability was for Alzheimer's. The study included sixty-five pairs of twins, both monozygotic and dizygotic twins, that either one or both of the twins had dementia. The concordance rate for monozygotic twins was 67 percent where as the dizygotic rate was 22 percent. According to this article, the estimated heritability for Alzheimer's is .74. The differences of when the onset of Alzheimer's came in the twins may be because of environmental factors. There is more known about the genetic effects of early onset Alzheimer's then known about late onset Alzheimer's. The influence of selection on Alzheimer's would not have a big impact because onset of Alzheimer's is after reproductive age. If there is a history of Alzheimer's in the family, a couple may choose not to have kids or adopt so that they would not be passing on the trait.

http://www.ncbi.nlm.nih.gov/pubmed/9060980- Heritability for Alzheimer's disease: the study of dementia in Swedish twins

2. What effect might inbreeding have on this disorder?
Since Alzheimer's has a heritability of .74, the effect of inbreeding may be substantial. The more inbred a population is, the higher the heritability could potentially be. The heterozygosity would go down, so there would be little variation in alleles.