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\citet{25158072} reported a genome-wide association study (GWAS) from 1,310 people with OCD, 834 with Tourette syndrome, 579 with both OCD and a chronic tic disorder, and over 5,500 controls matched for ancestry. A significant polygenic component was identified for OCD without tics, but not for the combined patient group or other subgroups. Overall, this study is consistent with previous work but it provided disappointingly few novel results.  An international study examined tic symptoms in the United States and the Netherlands \citep{25714449}. Three factors were identified: complex vocal tics and obscene behavior, body tics, and head/neck tics. Heritability There  was considered moderate no evidence of heritability for the second factor while the h2r was approximately 0.2  for the first and third factors, h2r=0.21 factors when age  and 0.25 respectively. sex were included as covariates.  Heritability for these  narrower tic phenotypes is considerably lower than the heritability estimates obtained estimates, which range up to 0.65,  when comorbid conditions, such as OCD and ADHD are included, which results in heritability estimates of up to 0.65. included.  These results support the argument that OCD and ADHD cannot easily be separated from tics in people with TS. ### Environmental risk factors