Handedness in mental handicap: investigation into populations of Down's syndrome, epilepsy and autism.

The handedness in three randomly sampled groups of people with learning disabilities consisting of patients with Down's syndrome, epilepsy, and autism were studied using a validated instrument. All subjects were controlled for neurological and other medical disorders. A statistically significant increase in left-handedness and ambiguous handedness compared with the general population was found in all groups. There was no significant difference in the rate of left-handedness between the three groups.