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Background: The genetic foundations of sleep disorders are manifold. Most forms of sleep disorder are multifactorial diseases and single gene defects are not expected to be responsible as candidate genes in the sense of Mendelian inheritance of the disease. The discovery of isolated monogenetic associations to sleep disorders will also be a rarity even in the future. Against this background, molecular genetic diagnostics are currently a little used diagnostic instrument in sleep medicine. Objectives: This article presents an overview of the molecular genetic results, which already have a relevant importance in the diagnostics of isolated sleep disorders and molecular genetic results which can contribute to strengthening a suspected diagnosis in the context of the clinical and electrophysiological (polysomnography) results. Results and discussion: The well-known association of HLA loci with narcolepsy and the less significant association of HLA loci to other sleep disorders, such as sleepwalking and the Kleine-Levin syndrome may help to strengthen the diagnostic evidence to differentiate them from other possible diagnoses. For the group consisting of restless legs syndrome, periodic limb movements and the most commonly diagnosed form of sleep-related disorders, obstructive sleep apnea syndrome, molecular genetic findings do not have any diagnostic impact: however, there are many findings from large cohorts relating to associations with various genes but the biological significance is not yet fully understood. For clinicians working in the field of sleep medicine the molecular genetic findings concerning these sleep disorders are mainly important to obtain a better understanding of the biology, such as in insomnia and hypersomnia with the exception of narcolepsy. The group of clock genes may be of interest to better understand the biological basis of these sleep disorders as data on differential expression in idiopathic hypersomnia are available. [ABSTRACT FROM AUTHOR]

Abstract Genetic improvement in traits associated with seasonal breeding in sheep is challenging because these traits have low heritabilities, are generally not expressed until late in life, are commonly recorded only in females, and are expressed only in some lambing seasons and management systems. Detection of quantitative trait loci and their use in marker-assisted selection could therefore substantially enhance selection responses. A population of sheep with an extended breeding season was developed through selection for fertility in spring matings and provides opportunities for further study of candidate genes influencing seasonal breeding. In particular, the melatonin receptor 1a gene is polymorphic in many sheep breeds and appears to influence a number of seasonal reproductive responses. In addition, a variety of clock genes have been identified in laboratory mammals and shown to influence biological rhythms. Mutations in these clock genes have been identified and shown to influence circadian periodicities and reproductive patterns in golden hamster and mouse. In sheep, expression of clock genes in the suprachaismatic nucleus and pars tuberalis (PT) suggests that "calendar" cells in the ovine PT play a role in maintaining circannual rhythms. Thus the various clock genes represent potentially important candidate genes that may be involved in control of seasonal breeding.