Sleep-onset vasomotor myoclonus: Reframing chronic hypnic jerks through a neurovascular lens—informed by case study and group trends

Background: Hypnic jerks are considered benign, transient motor events during sleep onset. However, in a subset of individuals, they evolve into chronic, disruptive episodes marked by neurovascular instability, autonomic dysregulation, and impaired sleep continuity. Because these symptoms superficially resemble common benign variants, severe forms remain under-recognized and lack a formal diagnostic classification. Results: This paper introduces Sleep-Onset Vasomotor Myoclonus (SOVM), a proposed condition defined by myoclonic bursts at sleep transition accompanied by vasomotor delay, impaired baroreflex adaptation, and oscillatory cerebrovascular instability. A 22-year case review synthesizes structural, autonomic, endocrine, immune, and genetic findings into a unified neurovascular framework. Objective data revealed delayed sympathetic vasoconstriction, cervical/CSF flow vulnerability, episodic RAAS underactivity, and neuronal hyperexcitability responsive to ion-channel modulation. Genomic analyses from the broader patient community add a new dimension: 55 individuals with chronic sleep-onset myoclonus have undergone whole-genome sequencing, and every dataset demonstrates unresolved or atypical structural complexity within the RCCX locus —a multiallelic region containing CYP21A2 , TNXB , C4A , and C4B . Among those who underwent targeted CAH testing , all six showed a CYP21A2 duplication , a classic RCCX rearrangement associated with altered steroidogenesis, variable RAAS signaling, connective-tissue fragility, and complement dysregulation. These domains parallel clinical observations in the index case, including low Angiotensin II, cervical mechanical sensitivity, C4/C4a elevation, and blood-brain barrier vulnerability. Taken together, the RCCX signal suggests a shared structural-genetic susceptibility that may amplify neurovascular tone instability at sleep onset. Conclusions: SOVM may represent a distinct sleep-transition disorder rooted in neurovascular mismatch—a failure to synchronize neuronal and vascular tone during the transition into sleep. Integrating community-level genomic findings, especially RCCX structural variation and CYP21A2 duplication patterns, strengthens the hypothesis of a multifactorial susceptibility spanning RAAS, connective tissue, immune, and autonomic pathways. Recognizing SOVM as a coherent phenotype may facilitate mechanism-based treatment strategies and motivate cross-disciplinary research into cerebrovascular–autonomic dynamics during sleep initiation.