FASPS is the first disorder to link known core clock genes directly with human circadian sleep disorders. As the PER2 mutation is not exclusively responsible for causing FASPS, current research has continued to evaluate cases in order to identify new mutations that contribute to the disorder. Mechanisms (Per2 and CK1)
Two years after reporting the finding of FASPS, Ptáčeks and Fus groups published results of genetic sequencing analysis on a family with FASPS. They genetically mapped the FASPS locus to chromosome 2q where very little human genome sequencing was then available. Thus, they identified and sequenced all the genes in the critical interval. One of these was Period2 (Per2) which is a mammalian gene sufficient for the maintenance of circadian rhythms. Sequencing of the hPer2 gene (h denoting a human strain, as opposed to Drosophila or mouse strains) revealed a serine-to-glycine point mutation in the Casein Kinase I (CK1) binding domain of the hPER2 protein that resulted in hypophosphorylation of hPER2 in vitro. The hypophosphorylation of hPER2 disrupts the transcription-translation (negative) feedback loop (TTFL) required for regulating the stable production of hPER2 protein. In a wildtype individual, Per2 mRNA is transcribed and translated to form a PER2 protein. Large concentrations of PER2 protein inhibits further transcription of Per2 mRNA. CK1 regulates PER2 levels by binding to a CK1 binding site on the protein, allowing for phosphorylation which marks the protein for degradation, reducing protein levels. Once proteins become phosphorylated, PER2 levels decrease again, and Per2 mRNA transcription can resume.
Fruit flies and mice engineered to carry the human mutation also demonstrated abnormal circadian phenotypes, although the mutant flies had a long circadian period while the mutant mice had a shorter period. The genetic differences between flies and mammals that account for this difference circadian phenotypes are not known. Most recently, Ptáček and Fu reported additional studies of the human Per2 S662G mutation and generation of mice carrying the human mutation. These mice had a circadian period almost 2 hours shorter than wild-type animals under constant darkness. Genetic dosage studies of CKIδ on the Per2 S662G mutation revealed that depending on the binding site on Per2 that CK1δ interacts with, CK1δ may lead to hypo- or hyperphosphorylation of the Per2 gene. See also
Delayed sleep phase disorder
Irregular sleep–wake rhythm
Non-24-hour sleep–wake disorder

References


== External links ==