Open Label Study Investigating Safety and Efficacy of NPL2009 50 mg - 150 mg on Prepulse Inhibition Tests and Continuous Performance Tasks, 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