Left-handedness: association with immune disease, migraine, and developmental learning disorder.

We report an experimental study designed to test the following hypothesis derived from clinical observations: There is an elevated frequency in left-handed individuals and in their families of immune disease, migraine, and developmental learning disorders. In two separate investigations the frequency of these conditions was compared in strongly left-handed subjects and in strongly right-handed controls. In each of the investigations we found markedly higher frequencies of immune disease in the left-handers than in the right-handers. The rate of learning disabilities was also much higher in the left-handers than in the right-handers in both investigations. In a second study the frequency of left-handedness was compared in patients with migraine or immune disease and in general population control subjects free of these disorders. There was a higher frequency of left-handedness in patients with migraine and myasthenia gravis than in controls. We present a brief outline of a hypothesis that may account for an increased frequency of immune disease in left-handers and in their families.