Thinking positively: The genetics of high intelligence

Can someone explain this for someone like me with no education in biology or psychology?

For mentally challenged people, researchers have done an analysis of the distribution of certain genes that are associated with the handicap. They have shown with high likelihood that mental handicap is actually different than just being on the low end of the intelligence distribution.

This study tries to answer the question, "is the same true for high intelligence?" The two general theories are the Continuity Hypothesis and Discontinuity Hypothesis. As its name suggests, the Continuity Hypothesis predicts that the high end of the intelligence distribution is continuous; extremely intelligence individuals don't violate the intelligence distribution the way mentally challenged people do. The Discontinuity Hypothesis predicts the opposite.

By analyzing the genes of twins and other close family members, the researchers found strong evidence of the Continuity Hypothesis.