The study will investigate the effects and the safety of a single-dose of ABX-1431 HCl on tics and other symptoms of Tourette Syndrome.

During part 1 (periods 1 and 2) each patient will receive study drug once and placebo once.

Patients who complete part 1 with adequate clinical safety will be offered the option to participate in part 2 (periods 3 and 4) and again willl receive study drug once and placebo once where, in contrast to part 1, administration will take place with a standard high fat meal.

This is a single dose, double-blind, randomized, placebo-controlled, cross-over study. This study will assess the single dose effects of ABX-1431 HCl on tics and other symptoms of Tourette Syndrome.

All patients will undergo a screening visit for enrollment criteria. Eligible patients will be treated with a single dose of ABX-1431 HCl or placebo followed by efficacy, safety and pharmacokinetics assessments. After a washout period of 1-3 weeks, patients will undergo identical procedures with the other treatment.

Only patients who complete the first part of the study with adequate clinical safety will be offered the option to participate in an additional two period crossover, where ABX-1431 HCl or placebo is taken with a standard high fat meal. Again, efficacy, safety and pharmacokinetics assessments will be done. After a washout period of 1-3 weeks, patients will undergo identical procedures with the other treatment.

This study will enroll 20 patients with a diagnosis of Tourette Syndrome OR chronic motor tic disorder.

Principal Inclusion Criteria:

• Patient is a male or female between the age of 18 and 65 years of age at the Screening Visit.
• Patient has a diagnosis of Tourette Syndrome OR chronic motor tic disorder as defined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria.
• Patient's Yale Global Tic Severity Scale (YGTSS) total tic sub-scale (TTS) results must be ≥ 18 (Range 0-50) at the Screening Visit.
• Patients taking daily medications for symptoms of Tourette Syndrome [e.g. neuroleptics (e.g. aripiprazole, risperidone) or selective serotonin reuptake inhibitors (e.g. fluoxetine)] must be on a stable dose of medication for at least 30 days before the Screening Visit and must be expected to remain on a stable dose during this study.

Principal Exclusion Criteria:

• Patient is taking potent cytochrome P450 3A4/5 inducers [e.g. carbamazepine, oxcarbazine, rifampin, St. John's Wort (Hypericum perforatum), or phenytoin]. Patient is taking strong P450 3A4/5 inhibitors including atazanavir, bocepravir, clarithromycin, grapefruit juice, indinavir, itraconazole, ketoconazole, nefazodone, nelfinavir, posaconazole, ritonavir, saquinavir, telithromycin, or voriconazole.
• Patients with a diagnosis of any psychiatric comorbidity (obsessive compulsive disorder, attention deficit hyperactivity disorder) OR generalized anxiety disorder, depression or post-traumatic stress disorder that is unstable or requires alteration in therapy are excluded. Patients with a past history of psychosis or schizophrenia at any time are excluded. Patients with stable OCD or ADHD requiring no alteration in therapy may be enrolled.