Despite strong evidence for a genetic contribution to Tourette disorder (TD), progress in the identification of specific risk genes has been, until quite recently, halting. However, building upon NIMH's support for our initial efforts to ascertain TD trios as well as our highly successful experience with genomic investigations of autism spectrum disorders (ASD), we have now demonstrated a clear path forward for reliable, systematic gene discovery in TD. Our TD work, recently published in the journal Neuron, identified one high confidence and three probable novel TD risk genes collectively pointing to neurite outgrowth and axon pathfinding as potential pathological mechanisms1. More importantly, however, our findings demonstrate, for the first time, a clear excess of de novo damaging point mutations in individuals with TD, with effect sizes that rival our recent findings in ASD. This discovery strongly suggests that sequencing of larger cohorts will reliably and rapidly lead to the identification of many more highly penetrant risk genes. Moreover, our recent work suggests an increased yield of highly penetrant damaging de novo variants in probands who are affected both with TD and obsessive compulsive disorder or attention deficit hyperactivity disorder, suggesting that our efforts may well also offer avenues to study the overlap in genetic risks for these often-comorbid conditions. Our current application proposes to: (1) expand our well characterized TD trio cohort by an additional 1,000 simplex trios and make the phenotypic data and biological materials widely and rapidly available to the broad scientific community; (2) accelerate gene discovery, via genotyping (for large de novo CNV identification) and whole exome sequencing (for de novo single nucleotide variant, insertion/deletion variant, and small CNV identification) of these additional TD trios, making these data rapidly and widely available as well; (3) extend the process of in silico and in vitro genomics investigations to elaborate the biology of TD with the long term goal of developing novel and more effective treatment strategies; and (4) begin biological characterization of TD variants using iPSC-derived neuronal cells. Given the potentially debilitating nature of TD alone, and a population prevalence of approximately 1 in 100 individuals, such advances would confer a significant public health benefit. The study design again rests heavily on the collaborative R01 mechanism that will bring together deep experience with the TD phenotype at multiple sites across the globe with scientists with a strong track record of success in rare variant human genomics and gene discovery. Specifically, the proposal includes seven primary US sites, four direct subcontracts (two USA sites for clinical supervision and data analysis and two foreign coordinating sites), and fourteen secondary clinical sites within Europe and South Korea.
Tourette disorder (TD) is a poorly understood, often debilitating developmental neuropsychiatric disorder, characterized by a combination of persistent vocal and motor tics, affecting between 0.3 to 1% of people worldwide. Our international team of collaborating clinicians and geneticists has established the contribution of new (de novo) variants to TD risk and demonstrated that the continued identification of recurrent de novo variants, via sequencing of the protein coding segment of the genome, is a reliable, systematic path forward for gene discovery. Therefore, our group plans to recruit 1,000 additional parent-child simplex trios, sequence these families, identify additional high confidence TD genes, and begin the process of leveraging these molecular clues to elaborate the biological basis of TD, while making all the collected biomaterials, clinical and genomic data rapidly available to the broad scientific community.
