The Genetic Epidemiology for Tics

Grant Type
Grant Year
Institution Location
Institution Organization Name
VU Medical Center The Netherlands
Investigators Name
Cath, Danielle, MD, PhD

Tics and Tourette Syndrome (TS) often appear to be more frequent in some families than in the general population. This suggests that either tics have a hereditary component or that family members may unconsciously “copy” tics from each other. To disentangle the environment influence from a genetic effect, twin studies are useful. In these studies the association of a trait (in our case tics), are compared between monozygotic (MZ) twin-pairs (twins with identical DNA) and dizygotic (DZ) or fraternal twin-pairs, who share half of their DNA. When a trait is genetic, MZ twins are more likely to share that trait than DZ twins. When the trait is found equally in both MZ and DZ twin-pairs, then we may assume that the family environment is probably causing the similarities. The aim of this study is to investigate the contribution of genes and the environment on tics and TS in a large epidemiological sample of adult Dutch twins, their siblings, parents and spouses. Only one small clinical study of 43 twin pairs with TS has been reported. In that study, 30 twins were monozygotic and 13 were dizygotic. Similarity rates for TS were 53% for MZ pairs and 8% for DZ pairs. When criteria were broadened to include tics of any type, rates increased to 77% for MZ pairs and 23% for DZ pairs. Similarity rates for co-morbid Obsessive Compulsive Disorder (OCD) symptoms were 52% for MZ pairs and 15% for DZ pairs. These findings strongly indicate a genetic basis for both tics and co-morbid OCD. They also suggest that environmental factors (such as low birth weight and maternal smoking during pregnancy) may affect tic expression. To date, no large-scale epidemiological twin studies have investigated the relative contribution of genes and environmental factors on tic expression. The Dutch National Twin Registry is a population-based twin register that was established by Prof. Boomsma in 1987 at the Free University in Amsterdam. Currently over 30,000 twins and their family members (including parents, siblings, spouses and children) are registered. Each 2-4 years, a questionnaire on health, lifestyle, emotional and social factors is sent to registrants. This TSA funding has enabled us to include some additional questions about tic-symptoms in the next questionnaire that will be distributed in the fall of 2008. Information learned should elucidate the contribution of genes and environment to tics and TS. Danielle Cath, M.D., Ph.D., Dorret I. Boomsma, Ph.D. VU Medical Center, Amsterdam, The Netherlands Award: $75,000 Tourette Association of America Inc. – Research Grant Award 2008-2009