PROK2 is expressed in the suprachiasmatic nucleus (SCN) and has been proposed to have a role in the regulation of circadian rhythms.17 Circadian rhythm alterations have been shown to correlate with cognitive impairment in HD36 and in HD models pharmacological imposition of sleep slows cognitive decline and reverses deregulation of PROK2. 37 As a blood marker of HD progression PROK2 is very promising, since this could also be reflecting brain changes. This evidence concerns the gene PROK2 and Huntington disease.