Delayed sleep phase disorder and advanced sleep phase disorder cause disruption of the circadian clock and present with extreme morning/evening chronotype with unclear role of the genetic etiology, especially for delayed sleep phase disorder. To assess if genotyping can aid in clinical diagnosis, we examined the presence of genetic variants in circadian clock genes previously linked to both sleep disorders in Slovenian patient cohort. Based on Morning-evening questionnaire, we found 15 patients with extreme chronotypes, 13 evening and 2 morning, and 28 controls. Sanger sequencing was used to determine the presence of carefully selected candidate SNPs in regions of the,andgenes. In a patient with an extreme morning chronotype and a family history of circadian sleep disorder we identified two heterozygous missense variants ingene, c.1243C>G (NM_001377275.1 (p.Pro415Ala)) and c.1250A>G (NM_001377275.1 (p.His417Arg)). The variants were significantly linked to Advanced sleep phase disorder and were also found in proband's father with extreme morningness. Additionally, a rare SNP was found ingene in a patient withDelayed sleep phase disorder. The novel variant in(NM_022817.3):c.1901-218 G>T. We identified a family with autosomal dominant inheritance of twoheterozygous variants that can be linked to Advanced sleep phase disorder. We revealed also a rare hereditary form of Delayed sleep phase disorder with a newvariant with autosomal dominant inheritance, shedding the light into the genetic causality. CSNK1D PER2/3CRY1PER3PER2clinical picture of PER2was found in proband's parent with eveningness, indicating an autosomal dominant inheritance PER3PER2
