Birth weight discordance, gene expression, and DNA methylation: A scoping review of epigenetic twin studies
Bibliographic record
Abstract
BACKGROUND: Birth weight is considered as an important indicator of environmental conditions during prenatal development. Molecular mechanisms, including epigenetic modifications, play central roles in the body's adaptation to ever-changing environmental conditions. Twin study designs offer a powerful approach for distinguishing environmental from genetic effects. Specifically, within-pair comparisons of monozygotic twins can be used to differentiate unique individual environmental factors from shared environmental and genetic contributions. Notably, numerous studies in monozygotic twins have shown associations between prenatal environment and birth weight discordance (BWD), and suggested a potential involvement of gene expression and epigenetic factors mediating the association. OBJECTIVE: To conduct a scoping review of the literature on definitions of BWD and on epigenetic modifications and gene expression changes associated with BWD in twins. METHOD: Following PRISMA guidelines, we searched PubMed and Ovid MEDLINE(R) databases and included 34 twin studies focusing on birth weight and epigenetic or gene expression outcomes. RESULTS: There is a lack of consensus on BWD values when comparing groups of twins for their risks of perinatal mortality and morbidity, which vary between 15-30% depending on the type of placentation and gestational age. The gene expression twin studies measured mostly metabolism-related candidate genes in placental tissues. Only small-scale twin studies measured BWD associated with gene expression patterns on genome-wide level using neonatal cells. Most DNA methylation twin studies conducted epigenome-level analyses, and studies differ substantially in terms of tissue type and age of the children. Differences in DNA methylation patterns measured in blood or saliva samples of the twins later in life were mostly in genes related to signal transduction, cell differentiation and proliferation processes. CONCLUSION: Transcriptional changes of placental glucose transporters and hypoxia-induced proteins possibly reflect compensatory processes in twin pregnancies. Gene ontology analysis of the differentially methylated genes associated with BWD pointed to transcription regulation and tissue development.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.015 | 0.071 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.006 | 0.004 |
| Bibliometrics | 0.019 | 0.018 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.002 | 0.003 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".