Another reason for possible reduction in sleep-related GH levels in HD gene carriers may be linked to a reduction in the night-time melatonin release we observed in these cohorts [99], since it has been shown that melatonin administration increases basal GH release and GH responsiveness to GHRH, possibly by inhibiting endogenous somatostatin release at the hypothalamic level [100,101]. This evidence concerns the gene GHRH and Huntington disease.