...Some people may be genetically predisposed to SAD, but the environment can trigger it as well, said Ignacio Provencio, a biology professor at the University of Virginia. A recent study led by Provencio shows that a genetic mutation in the eye could play a role in seasonal affective disorder. The mutation makes a person with SAD less sensitive to light. ... The information may also help predict which people with seasonal affective disorder will respond to light therapy, because the mutated genes involve light sensitivity, he said.