Tasimelteon for the Treatment of Non-24-hour Sleep-Wake Disorder (N24HSWD) in Blind Individuals With no Light Perception

Non-24-Hour Sleep-Wake Disorder (N24HSWD) occurs when individuals are unable to synchronize their endogenous circadian pacemaker to the 24-hour light-dark cycle, and the timing of their circadian rhythm instead reflects the intrinsic period of their endogenous circadian pacemaker. As a result, the circadian rhythm of sleep-wake propensity in these individuals moves gradually later and later each day if there circadian period is \> 24 hours and earlier and earlier is \< 24 hours. These individuals will be able to sleep well at night when their sleep-wake propensity rhythm is approximately aligned with the 24-hour light-dark and social cycle. However, after a short time, the endogenous sleep-wake propensity rhythm and the 24-hour light-dark cycle will move out of synchrony with each other, and they may have difficulty falling asleep until well into the night. In addition to problems sleeping at the desired time, the subjects experience daytime sleepiness and daytime napping. As time progresses, the endogenous circadian rhythm of sleep-wake propensity in these individuals moves further and further away from the 24-hour light-dark cycle and gradually, these individuals are unable to sleep at night and as a result experience extreme sleepiness during the daytime hours and more frequent naps with a longer duration. Eventually, the sleep-wake time moves back into alignment with the social time for sleep and the individuals sleep well at night and have decreased daytime napping. The alignment between their endogenous circadian rhythms and the 24-hour day is temporary as they are continually drifting later and later each day. The study is comprised of one 24-month treatment phase, as all subjects enrolled in the trial have already been diagnosed with N24HSWD. Frequency of study visits will depend on the subject's prior length of exposure to tasimelteon; accordingly, subjects will be assigned to one of two groups upon enrollment into the study. The short-term exposure group will consist of subjects for which it is possible at screening that they have been exposed to tasimelteon for less than 6 months. The long-term exposure group will consist of subjects who have more than 6 months of exposure to tasimelteon. After completion of the 24-month treatment phase, subjects have the option to enroll into the optional open-label extension sub-study for an additional 52 weeks. Frequency of visits will be identical regardless of previous exposure (short term/long term).