There has been no conclusive, scientific evidence that any part of a vaccine causes autism. A link was initially suspected by some because the first symptoms of autism emerge around the time children receive vaccinations. This link has been thoroughly reviewed, studied, and rejected by scientific consensus, and some of the original research purporting this link has been repudiated. Recent studies have shown that autism is tied to genes that influence brain cell connections. Although the identity of all the genes responsible for autism spectrum disorders is not yet known, scientists continue to seek genetic factors that may cause autism.