REM sleep behavior disorder is most commonly associated with which category of neurodegenerative diseases?

• A. Synucleinopathies (e.g., Parkinson's disease)
• B. Tauopathies (e.g., Alzheimer's disease)
• C. Prion diseases
• D. Huntington's disease

Answer: (A)

REM sleep behavior disorder happens when the normal REM sleep atonia fails, so people act out their dreams. The strongest and most consistent link is with synucleinopathies—neurodegenerative diseases driven by abnormal alpha-synuclein deposits. In Parkinson’s disease, as well as dementia with Lewy bodies and multiple system atrophy, alpha-synuclein pathology is central, and REM sleep behavior disorder often emerges years before motor symptoms in PD. This prodromal relationship makes synucleinopathies the best answer. Tauopathies, prion diseases, and Huntington’s disease have different underlying proteins and disease patterns, so REM sleep behavior disorder is not as characteristically associated with them.