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<b>BACKGROUND.</b> The circadian clock is a fundamental and pervasive biological program
that coordinates
24-hour rhythms in physiology, metabolism, and behavior, and it is essential to health.
Whereas therapy adapted to time of day is increasingly reported to be highly successful,
it needs to be personalized, since internal circadian time is different for each individual.
In addition, internal time is not a stable trait, but is influenced by many factors,
including genetic predisposition, age, sex, environmental light levels, and season.
An easy and convenient diagnostic tool is currently missing.
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<b>METHODS.</b> To establish a validated test, we followed a 3-stage biomarker development
strategy:
(a) using circadian transcriptomics of blood monocytes from 12 individuals in a constant
routine protocol combined with machine learning approaches, we identified biomarkers
for internal time; and these biomarkers (b) were migrated to a clinically relevant
gene expression profiling platform (NanoString) and (c) were externally validated
using an independent study with 28 early or late chronotypes.
</p><p id="d4360706e390">
<b>RESULTS.</b> We developed a highly accurate and simple assay (BodyTime) to estimate
the internal
circadian time in humans from a single blood sample. Our assay needs only a small
set of blood-based transcript biomarkers and is as accurate as the current gold standard
method, dim-light melatonin onset, at smaller monetary, time, and sample-number cost.
</p><p id="d4360706e395">
<b>CONCLUSION.</b> The BodyTime assay provides a new diagnostic tool for personalization
of health care
according to the patient’s circadian clock.
</p><p id="d4360706e400">
<b>FUNDING.</b> This study was supported by the Bundesministerium für Bildung und
Forschung, Germany
(FKZ: 13N13160 and 13N13162) and Intellux GmbH, Germany.
</p><p class="first" id="d4360706e406">
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