Nongenetic Factors in Gilles de la Tourette's Syndrome

To the Editor.— Interest in a possible hereditary component in the transmission and expression of Gilles de la Tourette's syndrome (TS) is longstanding. Although no specific genetic mechanism has been identified, several studies have reported a pattern of transmission that is consistent with an incompletely penetrant autosomal gene (D.L.P., J.F.L., unpublished data, 1985).¹⁻⁴The importance of nongenetic factors has also recently been emphasized by a twin study of TS reported by Price et al⁵in which seven (23%) of the 30 monozygotic pairs were fully discordant for TS. In preparing for a more extensive evaluation of these discordant twin pairs, we recently examined unpublished data from the original study and found that in each case the unaffected co-twin had a higher birth weight than the affected twin (Table). These data must be considered as preliminary, since detailed case histories of the twin pregnancies were not obtained as part