It has been determined that almost 3% of all our genes are devoted to smell. Although humans have about 1000 odor receptors, only about 40% are usable. Each time a new odor is encountered, a combination of receptors are stimulated. As a result, an infinte number of smells can be recognized by the receptors.
However, some ask whether this is an ethical practice. In my opinion, I do not think it would be ethical to provide gene technology to an individual to improve what was already normal. However, physiological changes brought about to allow a person to function normally are very welcome indeed!