Gene Hunting

strated that mental illnesses—such as schizophrenia, bipolar disorder, earlyonset depression, anxiety disorders, autism, and attention deficit hyperactivity disorder—have a genetic component. It is now clear that these disorders are not due to a single defective gene, but to the joint effects of many genes acting together with nongenetic factors. 1-3 Despite the daunting complexity, progress is being made. Researchers are hunting genes because they are likely to be a vital key to deciphering what goes wrong in the brain in mental illness.