A Standardized Four-Domain Operational Workflow for Postmortem Research in Initially Unexplained Infant Deaths

Purpose: Routine medicolegal autopsies generally do not include systematic assessment of hepatic CYP450 protein abundance, inflammatory markers, and oxidative stress markers as potential indicators of physiological vulnerability in initially unexplained sudden infant deaths. Building on the published five-domain Metabolic Vulnerability Index (MVI), this paper introduces a streamlined four-domain operational framework designed to facilitate standardized postmortem research while preserving medicolegal priorities. The immediate objective is to establish specimen-acquisition feasibility and measurement reproducibility. Longer-term objectives include calibration and validation of the proposed measurements and classification thresholds, followed by investigation of candidate mechanistic vulnerability patterns for concordance with clinical, developmental, environmental, and toxicologic contextual variables to inform subsequent hypothesis-generating studies.Methods: The operational MVI narrows the original framework to four biologically interconnected domains. Domain 1 assesses hepatic CYP450-mediated metabolic capacity indirectly through measurement of age-referenced CYP3A4, CYP2C19, and CYP2D6 protein abundance in qualified frozen liver. Domains 2 and 3 assess inflammation-associated processes through hepatic C-reactive protein (CRP) immunoreactivity and oxidative stress through 4-hydroxy-2-nonenal (4-HNE) protein-adduct immunoreactivity, respectively, using immunohistochemistry in formalin-fixed, paraffin-embedded liver tissue. Domain 4 addresses documented xenobiotic exposure through contextual interpretation of finalized routine forensic toxicology findings. The revised workflow eliminates additional research requirements for femoral venous blood and specifically oriented medulla/pons specimens. Original quantitative measurements and supporting assessment data are retained independently of their provisional Tier 0–3 classifications, preserving the underlying evidence for subsequent empirical analyses of distributions, variability, interdomain associations, and refinement of classification thresholds rather than reducing the data permanently to categorical scores. Specimen qualification, analytical evaluability, interpretive scorability, missing evidence, and scoring-rule versions are documented separately. Missing or unevaluable evidence is not assigned Tier 0 or interpreted as a normal finding.Results: The proposed framework specifies provisional Tier 0–3 classifications for each scorable domain. Complete four-domain profiles generate an unweighted composite MVI score ranging from 0 to 12 and one of 16 descriptive four-bit configurations representing candidate patterns of physiological vulnerability. The framework establishes standardized documentation requirements, scoring rules, and specimen-adaptive procedures intended to support consistent implementation across participating medicolegal investigations. These represent methodological outputs rather than empirically validated findings.Discussion: Consolidating three research measurements within hepatic tissue and incorporating existing forensic toxicology findings may reduce additional specimen demands and facilitate integration with routine autopsy procedures. This narrower approach preserves investigation of selected interconnected metabolic, inflammatory, oxidative, and exposure-related processes but excludes direct assessment of brainstem serotonergic and respiratory-autonomic vulnerabilities addressed by the original MVI. Prospective investigations must evaluate specimen acquisition, laboratory performance, reproducibility, personnel burden, potential autopsy delays, and incremental costs.Conclusions: The four-domain operational MVI provides a standardized, specimen-aware framework for investigating candidate physiological vulnerabilities in initially unexplained sudden infant deaths. Its operational feasibility, measurement reproducibility, and biological interpretability remain to be established through prospective investigation. The framework incorporates provisional, heuristically derived, literature-informed age-specific minimum-abundance thresholds for CYP450 proteins and investigator-selected immunohistochemical staining conventions. If reliable specimen acquisition and reproducible measurements can be demonstrated, subsequent adequately powered studies may empirically calibrate and validate these thresholds, characterize biological variability, and investigate candidate mechanistic vulnerability patterns and their concordance with contextual variables. The framework remains exploratory, is not a diagnostic test, and does not establish individual causation of death.