From epigenetic marks to biomarker qualification in fetal alcohol spectrum disorder: a critical review of DNA methylation, chromatin and regulatory RNA

INTRODUCTION: Fetal alcohol spectrum disorder (FASD) is a preventable cause of neurodevelopmental disability, yet diagnosis remains multidisciplinary and affected people may be identified late. Epigenetic research has expanded since the 2017-2018 primer series. AREAS COVERED: This critical narrative review evaluates DNA methylation, chromatin and regulatory RNA by tissue, developmental window, intended use and evidence maturity. An author-generated, unvalidated four-gate heuristic separates discovery, analytical validation, clinical validation and clinical utility. A fetal alcohol syndrome blood methylation classifier has promising development-stage evidence, while maternal extracellular-vesicle-associated microRNA remains a proof-of-concept prenatal candidate. Acetyl-CoA synthetase 2 (ACSS2) provides one experimentally supported metabolism-chromatin link in mice alongside other plausible mechanisms. Small cohorts, tissue differences, ancestry, parental exposure histories and limited independent validation constrain interpretation. EXPERT OPINION: No epigenetic assay reviewed here is suitable for stand-alone FASD diagnosis. Clinical utility discussions describe future research, not demonstrated benefit. Progress requires reproducible assays, independent evaluation in the intended population, and evidence that testing improves care without increasing stigma or inequity.