 The primary efficacy endpoint is the reduction from placebo-baseline in cortical arousal intensity associated with PLMs after treatment with GEn. A sample size of 20 subjects is estimated by a priori power analysis GPower 3.1.9.2 to achieve 92 power for a 2-sided 5 paired t-test with an effect size of 0.80. The primary efficacy analysis will be performed on the per-protocol population who completed the study taking 600 mg GEnday of the study drug. For subjects who prematurely withdraw from the study, EOS PSG will be acquired provided they received at least 2 weeks of treatment with GEn. All data for primary and secondary endpoints will be analyzed using a paired t-test. 95 confidence intervals will be provided for the true mean treatment difference. Descriptive statistics will be reported for the primary and secondary endpoints by placebo-baseline visit and treatment group. To further evaluate treatment effects, the association between the changes from baseline in primary objective and secondary subjective endpoints will be evaluated using Pearson correlation coefficients. Safety and tolerability analyses will focus primarily on frequency of treatment emergent adverse events. 