A few rare highly penetrant genetic mutations have been found that explain only a small number of cases in single families (the SLITRK1, HDC, and CNTNAP2 genes).Psychosocial or other non-genetic factors—while not causing Tourettes—can affect the severity of TS in vulnerable individuals and influence the expression of the inherited genes. Pre-natal and peri-natal events increase the risk that a tic disorder or comorbid OCD will be expressed in those with the genetic vulnerability. These include paternal age; forceps delivery; stress or severe nausea during pregnancy; and use of tobacco, caffeine, alcohol, and cannabis during pregnancy. Babies who are born premature with low birthweight, or who have low Apgar scores, are also at increased risk; in premature twins, the lower birthweight twin is more likely to develop TS.Autoimmune processes may affect the onset of tics or exacerbate them. Both OCD and tic disorders are hypothesized to arise in a subset of children as a result of a post-streptococcal autoimmune process. Its potential effect is described by the controversial hypothesis called PANDAS (pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections), which proposes five criteria for diagnosis in children. PANDAS and the newer pediatric acute-onset neuropsychiatric syndrome (PANS) hypotheses are the focus of clinical and laboratory research, but remain unproven. There is also a broader hypothesis that links immune-system abnormalities and immune dysregulation with TS.Some forms of OCD may be genetically linked to Tourettes, although the genetic factors in OCD with and without tics may differ.
The fourth revision of the DSM (DSM-IV) in 1994 added a diagnostic requirement for "marked distress or significant impairment in social, occupational, or other important areas of functioning", which led to an outcry from TS experts and researchers, who noted that many people were not even aware they had TS, nor were they distressed by their tics; clinicians and researchers resorted to using the older criteria in research and practice. In 2000, the American Psychiatric Association revised its diagnostic criteria in the fourth text revision of the DSM (DSM-IV-TR) to remove the impairment requirement, recognizing that clinicians often see people who have Tourettes without distress or impairment. Society and culture
Not everyone with Tourettes wants treatment or a cure, especially if that means they may lose something else in the process. The researchers Leckman and Cohen believe that there may be latent advantages associated with an individuals genetic vulnerability to developing Tourette syndrome that may have adaptive value, such as heightened awareness and increased attention to detail and surroundings.Accomplished musicians, athletes, public speakers and professionals from all walks of life are found among people with Tourettes.