Positive association of a Cry1 polymorphism with EDS

Introduction: Excessive daytime sleepiness (EDS) is the most common symptom related to organic, psychiatric and to other sleep disorders. It presents as the dissociation from the circadian rhythm and is the leading symptom of sleep disorders, which are summarized as hypersomnias of central origin. Our question was to what extent EDS, which could be interpreted as a symptom of a disturbed circadian rhythm may be linked to members of the clock genes. Therefore we performed an association study of Cry1.

Methods: We performed an association study in 86 German Caucasian patients (33 female, 53 male, mean age 39.3±13.7 years) suffering from EDS and 89 healthy controls (36 female, 53 male, mean age 53.0±9.0 years) in order to analyze if there is a genetic predisposition resulting from the involvement of sequence variants in the gene CRY1.

EDS as the cardinal clinical sign of central hypersomnia including narcolepsy was diagnosed in the Sleep Disorder Section of the University Clinics of Muenster, the Hephata Klinik in Schwalmstadt and the Klinikum Bremen Ost. The identification of SNPs was performed using sequence-based methods and by analysis of the Hapmap database. Genomic-DNA was extracted from peripheral blood using the blood mini kit (Qiagen GmbH, Hilden, Germany). Primers were designed for all protein coding exons of CRY1 (12 exons) using the program Exon Primer. PCR and sequencing was performed using standard protocols. Statistical calculations were performed using SPSS12.

Results: Seven known SNPs were identified in CRY1 (rs11113153, rs10861684, rs10861685, rs8192440, rs17289712, rs3809237 and rs10778533). A significant association with EDS was shown for one SNP in CRY1: rs17289712 (p=0.03). After adjustment for gender and age the significance levels became higher for rs17289712 (p=0.008).

Conclusion: The positively associated SNP rs17289712 is located c.158 + 17613 A>G in intron1 which is believed to contain some functionally essential regulatory elements. If EDS accounts for a syndrome that is caused by a malfunction of the circadian rhythm it is a possible explanation of this finding. A possible impact of the SNP could be on the regulatory level – a direct impact on the aminoacid sequence of the protein is unlikely. I remains to be confirmed in a larger sample cohort whether this positive finding is a coincidence or the consequence of a regulatory shift.