Which of the following is a circadian rhythm disorder type?

• A. Delayed sleep-wake phase disorder is a type of circadian rhythm disorder.
• B. Shift-work disorder is a mood disorder.
• C. Jet lag disorder is not a circadian disorder.
• D. Advanced sleep-wake phase disorder is not circadian.

Answer: (A)

Circadian rhythm sleep-wake disorders occur when the body’s internal clock is out of sync with the external environment, leading to sleep timing problems and daytime impairment. Delayed sleep-wake phase disorder fits this pattern: a person’s natural sleep is significantly later than conventional norms, making it hard to fall asleep at a typical time and to wake up for obligations. This misalignment is a hallmark of a circadian rhythm disorder, not just a generic sleep issue.

The other statements mischaracterize the conditions. Shift-work disorder is a circadian rhythm sleep-wake disorder caused by rotating or night work disrupting normal sleep timing, not a mood disorder. Jet lag disorder results from crossing time zones and also reflects circadian misalignment. Advanced sleep-wake phase disorder involves an earlier-than-desired sleep and wake pattern, which is another circadian rhythm disorder. Therefore, identifying delayed sleep-wake phase disorder as a circadian rhythm disorder best matches the concept being tested.