This is an open label exploratory study to investigate the safety and effects of a single dose of NPL-2009(50 mg - 150 mg) on Prepulse Inhibition (PPI) Tests and Continuous Performance Tasks (CPT) in adults with Fragile X Syndrome

Inclusion Criteria:

• Male or female patients, 18 to 45 years of age.
• Diagnosis of Fragile X Syndrome.
• Females must demonstrate a negative pregnancy test at screening.
• Females of child-bearing potential must be using a medically accepted means of contraception or must remain abstinent for the duration of the study.
• Each Legally Authorised Representative (LAR, usually parent or caregiver) must have a level of understanding sufficient to provide written informed consent to all required study tests and procedures.
• Each patient must consent/assent (depending on center-specific procedures) to all required study tests and procedures.
• Permitted concomitant medications must be stable for at least 6 weeks prior to enrollment. The following concomitant medications are permitted: psychostimulants, SSRIs, atypical antipsychotics, anticonvulsants which do not have liver inducing effects, clonidine.
• Each patient must be able to swallow the capsules (2, 3 or 4) to be provided in the study.

Exclusion Criteria:

• Current treatment with anticonvulsants known to induce liver enzymes e.g. depakote
• Current treatment with N-methyl-D-aspartate (NMDA) antagonists
• Current treatment with tricyclic antidepressants
• Current treatment with typical antipsychotics
• Current treatment with lithium
• Patients planning to commence cognitive behaviour therapy during the period of the study or those who have begun cognitive behavioural therapy within 6 weeks prior to enrolment.
• History of, or current cardiovascular, renal, hepatic, respiratory and particularly gastrointestinal disease which may interfere with the absorption, distribution, metabolism or excretion of the study medication.
• History of, or current cerebrovascular disease or brain trauma.
• History of, or current significant endocrine disorder, e.g. hypo or hyperthyroidism.
• History of, or current malignancy.
• Presence of psychotic symptoms or lifetime history of schizophrenia, bipolar disorder, or other psychotic disorder, as assessed by the Investigator.
• Current major depressive disorder (patients must be free of the disorder for 3 months prior to enrolment).
• Judged clinically to be at risk of suicide (suicidal ideation, severe depression, or other factors), as assessed by the Investigator.
• Tourette's Disorder.
• Female patients who are either pregnant or nursing.
• Current drug abuse or dependence disorder or dependency in the 3 months prior to enrolment.
• Clinically significant abnormalities in safety laboratory tests, vital signs or EKG, as measured at screening
• Patients with significant hearing and/or visual impairments that may affect their ability to complete the test procedures
• Enrollment in another clinical trial within the previous 30 days