Article

Epigenetics

Epigenetics is the study of biochemical modifications that change how genes are expressed without altering the underlying DNA sequence. These modifications can be stable through cell divisions and, in some cases, may be transmitted across generations. Epigenetic mechanisms control cell identity, development and plasticity by regulating chromatin structure and access to the genetic code.

Main mechanisms

DNA methylation: addition of methyl groups (usually to cytosine bases) that commonly reduces gene transcription in promoter regions. See DNA methylation.
Histone modification: chemical changes to histone proteins (acetylation, methylation, phosphorylation etc.) that alter chromatin compaction and gene accessibility. See Histone modification.
Non-coding RNAs: short and long RNAs (microRNA, lncRNA, siRNA, piRNA) that regulate transcription, mRNA stability and translation. See Non-coding RNA.
Chromatin remodelling and higher‑order chromatin structure: ATP-dependent complexes and nuclear architecture that reposition nucleosomes and shape gene regulatory interactions.

Why epigenetics matters

Development: Epigenetic programmes drive differentiation (for example, how a fertilised egg produces neurons, muscle and skin) by switching suites of genes on or off.
Environment <> gene interaction: Nutrition, stress, toxins, medication and infection during critical windows (such as prenatal life) can alter epigenetic marks and influence health and behaviour.
Disease and ageing: Aberrant epigenetic marks are implicated in cancer, metabolic disease, neurodegeneration and some psychiatric and neurodevelopmental conditions.

Epigenetics and neurodevelopment

Epigenetic processes are central to brain development and plasticity. They help explain how the same genome produces diverse neural cell types and how experience (learning, stress, early adversity) can leave lasting molecular traces that change neural function.

Epigenetics and autism

Epigenetic variation is an active area of research in autism spectrum disorder (ASD). Epigenetic mechanisms may:

Modify the expression of autism-associated genes (either increasing or reducing expression).
Mediate environmental risk effects (for example, prenatal exposures or parental age) on neurodevelopment.
Contribute to sex differences through processes such as X‑chromosome inactivation, sex‑specific hormone effects on epigenetic enzymes, and genomic imprinting.

See also the focused summary: Epigenetics of autism.

Epigenetics and physical traits

Many external traits (skin pigmentation, tissue elasticity, adipose distribution, breast tissue composition) are shaped by both genetic sequence and epigenetic regulation. Hormones (oestrogen, progesterone), ageing and environmental exposures (UV radiation, smoking) commonly alter epigenetic marks and thereby influence phenotype.

Research and clinical implications

Biomarkers: Epigenetic signatures in blood or tissues are being investigated as disease biomarkers (for example, for cancer or neurodevelopmental risk).
Therapeutics: Drugs that modify epigenetic enzymes (histone deacetylase inhibitors, DNA methyltransferase inhibitors) are used in oncology and are being explored experimentally in other conditions. Their effects are broad and require careful evaluation.
Ethical issues: Because epigenetic marks can respond to environment and behaviour, findings can be misinterpreted. The field requires careful communication to avoid deterministic or stigmatizing conclusions.