METHOD OF IMPROVING SLEEP

1 . In a method of treating patients with a circadian rhythm sleep disorder (CRSD) consisting essentially of administering to said patients an amount of tasimelteon effective to treat said disorder, the improvement comprising:

selecting a patient for said treatment by identifying that said patient has a period 1 (PER1) loss-of-function (LOF) genotype associated with said disorder.

2 . The improvement of claim 1 , wherein said disorder is delayed sleep wake phase disorder (DSWPD).

3 . The improvement of claim 1 , wherein treating the patient includes administering tasimelteon to the patient once daily before bedtime.

4 . The improvement of claim 1 , wherein administering tasimelteon to the patient includes administering 20 mg of tasimelteon.

5 . The improvement of claim 1 , wherein treating the patient with tasimelteon improves at least one sleep parameter selected from a group consisting of: latency to persistent sleep (LPS); sleep efficiency (%) during the first, second, and/or final thirds of the night; rapid eye movement (REM) sleep duration; total sleep time (TST), including during the first two-thirds of the night; and wake after persistent sleep (WASO).

6 . A method for treating a patient exhibiting one or more symptoms of a circadian rhythm sleep disorder, which comprises:

identifying that said patient has a period 1 (PER1) loss-of-function (LOF) genotype associated with said disorder, and

administering an amount of tasimelteon to said patient effective to treat said disorder.

7 . The method of claim 6 , wherein said disorder is delayed sleep wake phase disorder (DSWPD).

8 . The method of claim 6 , wherein the amount of tasimelteon is 20 mg.

9 . The method of claim 6 , wherein treating said disorder includes improving at least one sleep parameter selected from a group consisting of: latency to persistent sleep (LPS); sleep efficiency (%) during the first, second, and/or final thirds of the night; rapid eye movement (REM) sleep duration; total sleep time (TST), including during the first two-thirds of the night; and wake after persistent sleep (WASO).

10 . A method for improving one or more sleep parameters in an individual, the method comprising:

identifying that said individual possesses a variant of the period 1 (PER1) loss-of-function (LOF) genotype associated with a circadian rhythm sleep disorder (CRSD); and

administering to said individual daily, at a time proximately before the individual's established bedtime, an amount of tasimelteon effective to improve one or more sleep parameters in said individual.

11 . The method of claim 10 , wherein the CRSD is delayed sleep wake phase disorder (DSWPD).

12 . The method of claim 10 , wherein the amount of tasimelteon is 20 mg.

13 . The method of claim 10 , wherein improving sleep includes improving at least one sleep parameter selected from a group consisting of: latency to persistent sleep (LPS); sleep efficiency (%) during the first, second, and/or final thirds of the night; rapid eye movement (REM) sleep duration; total sleep time (TST), including during the first two-thirds of the night; and wake after persistent sleep (WASO).