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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 was considered moderate for the first and third factors, h2r=0.21 and 0.25 respectively. Heritability for narrower tic phenotypes is considerably lower than the heritability estimates obtained when comorbid conditions, such as OCD and ADHD are included, which results in heritability estimates of up to 0.65. These results suggest support the argument  that OCD and ADHD cannot easily be separated from tics in people with TS.  ### Environmental risk factors