Lara:

Thanks for asking. This is undoubtably more than you wanted (and not all of the research is exactly on point) but it is the basis for the linkage between childhood stress and facial and other tics. And to clarify: The research does not state that childhood stress causes tics. It does, however, state that childhood stress can be a cause of tics and certainly can exacerbate tics. And that is consistent with my statements above.

Some of the research:

Bostic JQ, Prince JB. Child and adolescent psychiatric disorders. In: Stern TA, Rosenbaum JF, Fava M, Biederman J, Rauch SL, eds. Massachusetts General Hospital Comprehensive Clinical Psychiatry . 1st ed. Philadelphia, Pa: Mosby Elsevier; 2008:chap 69.

Jankovic J, Lang AE. Movement disorders: Diagnosis and assessment. In: Bradley WG, Daroff RB, Fenichel GM, Jankovic J, eds. Neurology in Clinical Practice . 5th ed. Philadelphia, Pa: Butterworth-Heinemann; 2008:chap 23.

Johnston MV. Movement disorders. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 597.

Franklin SA, Walther MR, Woods DW. Behavioral interventions for tic disorders. Psychiatr Clin N Am. 2010;33:641-655.

Also:

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th edition, text revision. Washington, DC: American Psychiatric Association,2000.

Kurlan, Roger, ed. Handbook of Tourette's Syndrome and Related Tic and Behavioral Disorders. New York: Marcel Dekker, Inc., 1993.

Leckman, James. F., and Donald J. Cohen. Tourette's Syndrome Tics, Obsessions, Compulsions: Developmental Psychopathology and Clinical Care. New York: John Wiley and Sons, Inc., 1999.

Robertson, Mary M., and Simon Baron-Cohen. Tourette Syndrome: The Facts. New York: Oxford University Press, 1998.

Chouinard, Sylvain, and Blair Ford. "Adult onset tic disorders." Journal of Neurology, Neurosurgery, & Psychiatry (June, 2000): 68.

Evidente, Virgilio G. H., M.D. "Is it a tic or Tourette's?: Clues for differentiating simple from more complex tic disorders." Postgraduate Medicine (October, 2000): 108.

Kurlan, R., M.D., and others. "Prevalence of tics in school-children and association with placement in special education." Neurology (October, 2001): 57.

Marcus, David, M.D., and Roger Kurlan, M.D. "Tic and its disorders." Movement Disorders (August, 2001): 19.

O'Connor, K. P., and others. "Evaluation of a cognitive-behavioural program for the management of chronic tic and habit disorders." Behaviour Research and Therapy (June, 2001): 39.

And psychological features distinguishing obsessive-compulsive and chronic tic disorders" Clinical Psychology Review (June, 2001): 21.