I agree with Alwayschanging about epigenetics. Science is learning much more about how genetics work and it seems that pretty much everything about a person comes down to how the environment impacts upon what genes they are born with.
With identical twins they have the exact same genes (you can't have boy/girl identical twins!) but how the genes express themselves is dependent upon the interactions with the physical and emotional environment. Identical twins will have the same susceptibility to a genetic disorder as each other but maybe only one twin will have that gene "switched on" by the physical or emotional interactions with the environment. That is why so many studies are done on identical twins, we have so much to learn about gene expression from them! Science is finding that there is a gene responsible for pretty much everything about our physical and psychological makeup. Emotional "hyper" sensitivity would be one for sure although I don't know if the gene responsible (or genes more likely) has been identified yet. I know there have been studies done on emotional response to music... they have found an emotional area of the brain that "lights up" in response to music in some people.... if they took the study further they would no doubt find the gene responsible for that emotional sensitivity to music by comparing that group of people to others who are not so emotionally responsive to music.