Circadian rhythm sleep disorder

CRSDs cause a persistent pattern of sleep/wake disturbances that arise either by dysfunction in one's biological clock system, or by misalignment between one's endogenous oscillator and externally imposed cues.

As a result of this misalignment, those affected by circadian rhythm sleep disorders can fall asleep at unconventional time points in the day, or experience excessive daytime sleepiness if they resist.

These occurrences often lead to recurring instances of disrupted rest and wakefulness, where individuals affected by the disorder are unable to go to sleep and awaken at "normal" times for work, school, and other social obligations.

These biological clocks control processes that fluctuate daily (e.g., body temperature, alertness, hormone secretion), generating circadian rhythms.

ipRGCs (intrinsically photosensitive Retinal Ganglion Cells), for example, are involved in modulating the circadian rhythm because of the expression of melanopsin, which absorbs light in the blue part (around 480 nm).

[5] Although these rhythms will persist in constant light or dark conditions, different zeitgebers (time givers such as the light-dark cycle) give context to the clock and allow it to entrain and regulate expression of physiological processes to adjust to the changing environment.

In order to be diagnosed with CRSD, there must be either a misalignment between the timing of the circadian oscillator and the surrounding environment, or failure in the clock entrainment pathway.

[10] Among people with typical circadian clock function, there is variation in chronotypes, or preferred wake and sleep times, of individuals.

Note that having a preference for extreme early or late wake times is not related to a circadian rhythm sleep disorder diagnosis.

The second category consists of disorders in which the external environment and the endogenous circadian clock are misaligned, called extrinsic type CRSDs.

[24] Therefore, further studies exploring this field have been highly recommended, mainly considering the increasing life expectancy and significance of neurodegenerative diseases in clinical practices.