['Clinical and genetic studies suggest circadian clock genes may contribute to biological mechanisms underlying alcohol use disorders (AUD). In particular, the Per2 gene regulates alcohol consumption in mutant animals, and in humans with AUD, the 10870 variant in PER2 has been associated with alcohol consumption. However, with respect to function, the molecular clock remains largely uncharacterized in AUD patients.', 'In skin fibroblast cultures from well-characterized human AUD patients (n = 19) and controls (n = 13), we used a bioluminescent reporter gene (Per2::luc) to measure circadian rhythms in gene expression at high sampling density for 5 days. Cells were genotyped for the PER2 10870 variant. The rhythm parameters period and amplitude were then analyzed using a case-control design and by genetic and clinical characteristics of the AUD subjects.', 'There were no differences between AUD cases and controls in rhythm parameters. However, period was inversely correlated with illness severity (defined as the number of alcohol dependence criteria met). The PER2 variant 10870 was not associated with differences in rhythm parameters.'] Does circadian clock period inversely correlate with illness severity in cells from patients with alcohol use disorders?