Editing Penetrance (section)

=== Epigenetic regulation ===
[[File:Epigenetic mechanisms.png|thumb|Illustration of epigenetic related methylation of histone tail. Giving cause to alterations. ]]
Sometimes, genetic alterations which can cause genetic disease and phenotypic traits, are not from changes related directly to the [[DNA]] sequence, but from [[Epigenetics|epigenetic]] alterations such as DNA [[methylation]] or [[Histone|histone modifications]]. Epigenetic differences may therefore be one of the factors contributing to reduced penetrance.<ref name=":0" /><ref name=":3" /><ref>{{Cite journal |last1=Safi-Stibler |first1=Sofiane |last2=Gabory |first2=Anne |date=1 January 2020 |title=Epigenetics and the Developmental Origins of Health and Disease: Parental environment signalling to the epigenome, critical time windows and sculpting the adult phenotype |url=https://www.sciencedirect.com/science/article/pii/S108495211830154X |journal=Seminars in Cell & Developmental Biology |series=SI: Chromatin dynamics in regeneration |volume=97 |pages=172–180 |doi=10.1016/j.semcdb.2019.09.008 |pmid=31587964 |s2cid=203849316 |issn=1084-9521 |url-access=subscription }}</ref> A study done on a pair of genetically identical [[Twin|monozygotic twins]], where one twin got diagnosed with [[leukemia]] and later on [[Thyroid neoplasm|thyroid carcinoma]] whilst the other had no registered illnesses, showed that the affected twin had increased methylation levels of the BRCA 1 gene. The research concluded that the family had no known [[DNA repair|DNA-repair syndrome]] or any other hereditary diseases in the last four generations, and no genetic differences between the studied pair of monozygotic twins were detected in the BRCA1 regulatory region. This indicates that epigenetic changes caused by environmental or behavioral factors had a key role in the cause of promotor hypermethylation of the BRCA1 gene in the affected twin, which caused the cancer.<ref>{{Cite journal |last1=Galetzka |first1=Danuta |last2=Hansmann |first2=Tamara |last3=El Hajj |first3=Nady |last4=Weis |first4=Eva |last5=Irmscher |first5=Benjamin |last6=Ludwig |first6=Marco |last7=Schneider-Rätzke |first7=Brigitte |last8=Kohlschmidt |first8=Nicolai |last9=Beyer |first9=Vera |last10=Bartsch |first10=Oliver |last11=Zechner |first11=Ulrich |last12=Spix |first12=Claudia |last13=Haaf |first13=Thomas |date=1 January 2012 |title=Monozygotic twins discordant for constitutive BRCA1 promoter methylation, childhood cancer and secondary cancer |journal=Epigenetics |language=en |volume=7 |issue=1 |pages=47–54 |doi=10.4161/epi.7.1.18814 |issn=1559-2294 |pmc=3329502 |pmid=22207351 }}</ref>