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Researchers used data from the Avon Longitudinal Study of Parents and Children to identify maternal psychological risk factors during pregnancy that increase the risk of tic disorders in offspring \citep{Ben_Shlomo_2015}. The Avon Longitudinal Study is an ongoing, prospective, pre-birth cohort study of all children born in Avon, United Kingdom, between April 1, 1991, and December 31, 1992. Maternal questionnaires were administered throughout pregnancy and they completed questionnaires about themselves and their children's development every 6 months from the child's birth to age 7 and then every year thereafter. In the final multivariate model, chronic maternal anxiety, evident both before and after parturition, was associated with TS or chronic tic disorder in their offspring. The authors suggest that this association may reflect shared genetic susceptibility or prenatal exposure.  An international study examined tic symptoms in the United States and the Netherlands \cite{25714449}. Three factors were identified: complex vocal tics and obscene behavior, body tics and head/neck tics. Heritability was considered moderate for the first and third factors, h24=0.21 and 0.25 respectively. Heritability for tic specific phenotypes is considerably lower than the heritability estimates for tic comorbid conditions such as OCD and ADHD for which heritability estimates of up to 0.65 have been obtained.