Fetal Rapid Eye Movement Sleep Dysfunction as a Potential Early Indicator for NALCN-Related CLIFAHDD Syndrome: A Case Report.

What's already known about this topic? ◦. NALCN variants, especially gain‐of‐function variants, increase neuronal excitability and reduce REM sleep. ◦. CLIFAHDD syndrome, caused by NALCN gain‐of‐function variants, includes congenital contractures, hypotonia, and developmental delay. What does this study add? ◦. This report provides detailed prenatal documentation of absent REM‐associated cycling and extremely low fetal heart rate (FHR) variability in a fetus with CLIFAHDD syndrome. ◦. We demonstrated the absence of FHR variability and REM sleep cycling as potential early indicators of autonomic and sleep state dysregulation. ◦. REM sleep loss may contribute to neurodevelopmental abnormalities in affected fetuses.