Poor lefties. It's not enough that they get teased in school playgrounds growing up, but it turns out that being left-handed also mean having increased risks of developing mental disorders:
Left-handedness appears to be associated with a greater risk for a number of psychiatric and developmental disorders. While lefties make up about 10% of the overall population, about 20% of people with schizophrenia are lefties, for example. Links between left-handedness and dyslexia, ADHD and some mood disorders have also been reported in research studies.
The reasons for this aren't clear. Scientists speculate it could be related to a concept known as brain lateralization. The brain has two halves. Each performs primarily separate, specialized functions, such as language processing, which mainly takes place in the left hemisphere. There is lots of communication between the hemispheres.