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Summary: Background: Mutations in THAP1 were recently identified as the cause of DYT6 primary dystonia; a founder mutation was detected in Amish–Mennonite families, and a different mutation was identified in another family of European descent. To assess more broadly the role of this gene, we screened for mutations in families that included one family member who had early-onset, non-focal primary dystonia. Methods: We identified 36 non-DYT1 multiplex families in which at least one person had non-focal involvement at an age of onset that was younger than 22 years. All three coding exons of THAP1 were sequenced, and the clinical features of individuals with mutations were compared with those of individuals who were negative for mutations in THAP1. Genotype–phenotype differences were also assessed. Findings: Of 36 families, nine (25%) had members with mutations in THAP1, and most were of German, Irish, or Italian ancestry. One family had the Amish–Mennonite founder mutation, whereas the other eight families each had novel, potentially truncating or missense mutations. The clinical features of the families with mutations conformed to the previously described DYT6 phenotype; however, age at onset was extended from 38 years to 49 years. Compared with non-carriers, mutation carriers were younger at onset and their dystonia was more likely to begin in brachial, rather than cervical, muscles, become generalised, and include speech involvement. Genotype–phenotype differences were not found. Interpretation: Mutations in THAP1 underlie a substantial proportion of early-onset primary dystonia in non-DYT1 families. The clinical features that are characteristic of affected individuals who have mutations in THAP1 include limb and cranial muscle involvement, and speech is often affected. Funding: Dystonia Medical Research Foundation; Bachmann–Strauss Dystonia and Parkinson Foundation; National Institute of Neurological Disorders and Stroke; Aaron Aronov Family Foundation. [Copyright &y& Elsevier]

Background: Tourette syndrome is a disorder characterized by persistent motor and vocal tics, and frequently accompanied by the comorbidities attention deficit hyperactivity disorder and obsessive-compulsive disorder. Impaired synaptic neurotransmission has been implicated in its pathogenesis. Our aim was to investigate the association of 28 candidate genes, including genes related to synaptic neurotransmission and neurotrophic factors, with Tourette syndrome., Methods: We genotyped 506 polymorphisms in a discovery cohort from the United States composed of 112 families and 47 unrelated singletons with Tourette syndrome (201 cases and 253 controls). Genes containing significant polymorphisms were imputed to fine-map the signal(s) to potential causal variants. Allelic analyses in Tourette syndrome cases were performed to check the role in attention deficit hyperactivity disorder and obsessive-compulsive disorder comorbidities. Target polymorphisms were further studied in a replication cohort from southern Spain composed of 37 families and three unrelated singletons (44 cases and 73 controls)., Results: The polymorphism rs3096140 in glial cell line-derived neurotrophic factor gene (GDNF) was significant in the discovery cohort after correction (P = 1.5 × 10(-4) ). No linkage disequilibrium was found between rs3096140 and other functional variants in the gene. We selected rs3096140 as target polymorphism, and the association was confirmed in the replication cohort (P = 0.01). No association with any comorbidity was found., Conclusions: As a conclusion, a common genetic variant in GDNF is associated with Tourette syndrome. A defect in the production of GDNF could compromise the survival of parvalbumin interneurons, thus altering the excitatory/inhibitory balance in the corticostriatal circuitry. Validation of this variant in other family cohorts is necessary., Competing Interests: Relevant conflicts of interest/financial disclosures: Nothing to report. Full financial disclosures and author roles may be found in the online version of this article., (© 2015 International Parkinson and Movement Disorder Society.)

Some twin studies suggest that substance initiation and dependence are part of a complex, two-stage process and that some genetic influences are stage-specific, acting on either the transition from abstinence to initiation, or on the transition from use to dependence. However, questions remain about the two-stage model, especially for illicit drugs. Using a familial aggregation design, we tested the hypothesized two-stage model of dependence on illicit substances and alcohol in a large, nationally representative sample. Family history of drug or alcohol problems is significantly associated with initiation that does not progress to dependence (i.e., conditional initiation). Furthermore, family history of drug or alcohol problems is significantly associated with dependence even after conditioning on factors influencing initiation (i.e., conditional dependence). These results suggest that substance initiation and dependence involve at least partially distinct familial factors. The possibility that different genetic factors affect initiation and dependence has important implications for control group selection in case-control genetic association studies, and may explain some inconsistent results for drug dependence. If some genetic factors are stage-specific (i.e., not common across initiation and dependence), inclusion of abstainers in the control group may mix the genetic effects for initiation with those for transition to dependence, providing unclear results. Depending on the specific question about the nature of the genetic effect (whether on initiation, on dependence, or both), investigators designing case-control genetic association studies should carefully consider inclusion and exclusion criteria of the control group.