Do identical twins show different ADHD epigenetics?

PostedOctober 8, 2025

UpdatedOctober 10, 2025

ByMy Patient Advice

Author: Victoria Rowe, MSc | Reviewed by: Dr. Rebecca Fernandez, MBBS

Yes, even though identical twins share 100% of their DNA, they can still differ in their expression of ADHD due to differences in ADHD twin epigenetics. These differences are often shaped by gene environment interactions, particularly through mechanisms like DNA methylation, which can turn genes on or off without changing the underlying genetic code.

Why do identical twins differ?

Identical twins can differ in ADHD traits because, despite sharing the same DNA, environmental influences, epigenetic changes, and life experiences shape how their genes are expressed.

Shared DNA, different environments

From womb conditions to childhood experiences, twins are exposed to subtle environmental differences. These can lead to epigenetic divergence changes in how genes are regulated, even when the DNA itself is identical.

Methylation and ADHD traits

Studies have found that methylation patterns can vary between twins, especially in genes linked to dopamine transport (DAT1) or receptor function (DRD4). In twin pairs where only one has ADHD, these differences may help explain the variation in symptoms.

Developmental timing matters

Epigenetic changes can emerge at different life stages. One twin might experience stress, illness, or a shift in parenting style that triggers a methylation change, while the other does not, leading to divergent developmental outcomes.

What this means for ADHD research

Twin studies have been essential in showing that epigenetics can bridge the gap between shared genetics and different outcomes. This not only advances our understanding of ADHD’s complexity but also reinforces the idea that environment and timing are just as critical as DNA.

Visit providers like ADHD Certify for personal consultations that consider both genetic and environmental influences on ADHD.

For a deeper dive into the science, diagnosis, and full treatment landscape, read our complete guide to Genetic studies and biomarkers.

Victoria Rowe, MSc

Author

Victoria Rowe is a health psychologist with a Master’s in Health Psychology and a BS in Applied Psychology. She has experience as a school psychologist, conducting behavioural assessments, developing individualized education plans (IEPs), and supporting children’s mental health. Dr. Rowe has contributed to peer-reviewed research on mental health, including studies on anxiety disorders and the impact of COVID-19 on healthcare systems. Skilled in SPSS, Minitab, and academic writing, she is committed to advancing psychological knowledge and promoting well-being through evidence-based practice.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the author's privacy.

Dr. Rebecca Fernandez, MBBS

Reviewer

Dr. Rebecca Fernandez is a UK-trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence-based approaches such as CBT, ACT, and mindfulness-based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well-being.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the reviewer's privacy.