Why Does the Same Mutation Kill One Person but Not Another?

Nearly all genetic disorders have different effects in different people, and individuals with a certain mutation can develop a disease while others with the same mutation may not. The extent to which a gene is turned on or off varies greatly among individuals. A recent study has demonstrated that this variation can have a significant impact on the phenotype of animals, and that its measurement can help to reliably predict the chances of developing an abnormal phenotype such as a disease. The study suggests that even if all of the genes important for a certain disease are completely understood, we may never be able to predict what will happen to individuals from their genome sequence alone. To develop personalized and predictive medicine it will also be necessary to consider the varying extent to which genes are turned on or off in each individual.

Link to the article:  http://www.sciencedaily.com/releases/2011/12/111207152310.htm