My 500th curation is a 2019 Portuguese human study of Azorean islanders:
“This study demonstrates a transgenerational epigenetic inheritance in humans produced by exposure to high TH [thyroid hormone] in fetal life, in the absence of maternal influences secondary to thyrotoxicosis. The inheritance is along the male line.
The present work took advantage of the relatively frequent occurrence of fetal exposure to high TH levels in the Azorean island of São Miguel. This is the consequence of a missense mutation in the THRB gene causing the amino-acid replacement R243Q, resulting in reduced affinity of the TH receptor beta (TRβ) for TH and thus RTHβ.
Its origin has been traced to a couple who lived at the end of the 19th century. F0 represented the third generation and F3 the sixth and seventh generation descendant.”
The study added evidence for human transgenerational epigenetic inheritance. However, the lead sentence in its Abstract wasn’t correct:
“Evidence for transgenerational epigenetic inheritance in humans is still controversial, given the requirement to demonstrate persistence of the phenotype across three generations.”
Although found in this study, there is no “requirement to demonstrate persistence of the phenotype.” Observing the same phenotype in each generation is NOT required for human transgenerational epigenetic inheritance to exist!
Animal transgenerational studies have shown that epigenetic inheritance mechanisms may both express different phenotypes for each generation:
- A study not cited in – but completely appropriate for – The lack of oxygen’s epigenetic effects on a fetus found heart disease effects in the F1 generation that were different from the heart disease effects found in the F2 and F3 generations;
and entirely skip a phenotype in one or more generations!
- Transgenerational pathological traits induced by prenatal immune activation found a F2 and F3 generation phenotype of impaired sociability, abnormal fear expression and behavioral despair – effects that weren’t present in the F1 offspring;
- The transgenerational impact of Roundup exposure “Found negligible impacts of glyphosate on the directly exposed F0 generation, or F1 generation offspring pathology. In contrast, dramatic increases in pathologies in the F2 generation grand-offspring, and F3 transgenerational great-grand-offspring were observed.” (a disease phenotype similarly skipped the first offspring generation);
- Epigenetic transgenerational inheritance mechanisms that lead to prostate disease “There was also no increase in prostate histopathology in the directly exposed F1 or F2 generation.” (a prostate disease phenotype skipped the first two male offspring generations before it was observed in the F3 male offspring); and
- Epigenetic transgenerational inheritance of ovarian disease “There was no increase in ovarian disease in direct fetal exposed F1 or germline exposed F2 generation. The F3 generation can have disease while the F1 and F2 generations do not, due to this difference in the molecular mechanisms involved.” (an ovarian disease phenotype similarly skipped the first two female offspring generations before it was observed in the F3 female offspring).
Details of epigenetic inheritance mechanisms were provided in Another important transgenerational epigenetic inheritance study. Mechanisms from fetal exposure to the fungicide vinclozolin were compared with mechanisms from fetal DDT exposure, and summarized as:
“The fetal exposure initiates a developmental cascade of aberrant epigenetic programming, and does NOT simply induce a specific number of DMRs [DNA methylation regions] that are maintained throughout development.“
I emailed references to the studies in the first five above curations to the current study’s corresponding coauthor. They replied “What is the mechanism for the transgenerational inheritance you describe?” and my reply included a link to the sixth curation’s study.
Are there still other transgenerational epigenetically inherited effects due to fetal exposure to high thyroid hormone levels?
https://www.liebertpub.com/doi/full/10.1089/thy.2019.0080 “Reduced Sensitivity to Thyroid Hormone as a Transgenerational Epigenetic Marker Transmitted Along the Human Male Line”