Stuttering and tics in twins.

A total of 63 twin pairs (22 MZ and 41 DZ), with one or both members affected by not organic stuttering and/or tics, have been drawn out of the Mendel Institute's twin file. Concordance of stuttering was observed in 10:12 MZ, but only in 2:19 DZ twin pairs; concordance of tics in 6:10 MZ and in 2:22 DZ twin pairs. Stuttering did not come out significantly associated either with other disturbances of language or with an IQ under the average; almost always it was possible to find out a precipitating factor. Significant relations between stuttering and tics could not be stated. Sex ratio, obtained regarding any affected subject separately, clearly turned in favour of males both in stuttering (32:12) and in tics (27:12). Stutterers and left-handers incidence in the families of stuttering subjects appeared significant in comparison with families of subjects with tics.