deletions | additions       diff --git a/Etiology.md b/Etiology.md  index 9fa0d01..bcbc8df 100644  --- a/Etiology.md  +++ b/Etiology.md 
...
### Environmental risk factors  Researchers used data from the Avon Longitudinal Study of Parents and Children to identify maternalpsychological risk  factorsduring 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 mothers also  completed questionnaires about themselves and their children's development every 6 months from the child's birth to the  age of  7 and then every year thereafter. In the final multivariate model, chronic maternal anxiety, evident both before and after parturition, the child's birth,  was associated with TS or chronic tic disorder in their offspring. children.  The authors suggest that this association may reflect shared genetic susceptibility or prenatal exposure.