How 30,000 twins are advancing research
December 3, 2025 - Shelly DeJong
When it comes to understanding why people have certain behaviors, traits and illnesses, twins are science’s superpower. That is why over 30,000 twins and their families from Michigan and surrounding states participate in Michigan State University’s Twin Registry.
The primary aim for researchers at the MSU Twin Registry is to examine how developmental differences in genetic, environmental, and neurobiological factors shape internalizing symptoms, such as eating disorders and depression, as well as externalizing symptoms, such as acting out behaviors.
Co-directed by Professors Alex Burt and Kelly Klump, the MSU Twin Registry, housed in MSU’s Department of Psychology, helps answer big questions about genetics, environment and health.
For over 24 years, the Twin Registry has served as a tool for a recruitment pool to earn grants totaling $45 million to date. The MSU Twin Registry and its participants have made invaluable contributions to better understanding prevention, treatment and support for individual and public health.
But why are twins so uniquely special for research?
The influence of genes and environment
Traits and disorders come from a mix of genes and the environment. Twin studies are one of the strongest tools we have for teasing apart those influences.
Here is how:
- Monozygotic, or identical, twins are the same sex and share 100% of their genes.
- Dizygotic, or fraternal, twins share on average 50% of their genes (just like regular siblings) and can be the same or opposite sex.
If identical twins are more similar to each other on a trait than fraternal twins are, it provides evidence that genes play a big role in shaping that characteristic. If identical and fraternal twins are equally similar, it indicates that environmental factors are more important.
Participants in the MSU Twin Registry span several developmental stages from early childhood to later adulthood, allowing researchers to identify age-specific risk factors for mental and physical disorders.
Another very cool side bonus — the scientific value of twins extends to their children. Because identical twins share all their genes, they are as genetically related to their co-twin’s children as they are to their own children! That also means that the children of one identical twin are genetic half-siblings with their cousins from the other twin. As cousins typically live in different households, this relationship allows for a unique perspective into possible interactions between genetic influences and environmental factors.
Impacting health care
Twin studies do not identify the location of specific genes, but they are extremely useful for understanding the extent to which psychological and medical disorders, as well as behaviors and traits, are influenced by genetic factors.
This knowledge can then be used to develop better ways to prevent and treat disorders like disordered eating or other maladaptive behaviors.
Some of the most effective medical interventions, including the ability to detect the early onset of breast cancer, have been developed in part because of twin study research.
An invitation to participate
Twin studies give researchers a rare insight into the complex interplay of genes and environment. They help answer some of the most fundamental questions about human development — and they do it in a way no other research method can.
The MSU Twin Registry is proud to be at the forefront of this work, partnering with thousands of twins to push our understanding of genes, environment and health.
If you’re a twin or a parent of twins, you are invited to participate. Your contributions can help us better understand the origins of traits, behavior and medical disorders, with the ultimate goal of informing treatment and prevention efforts for a variety of psychological and medical conditions.
Due to the unique characteristics twins share, your participation can have a meaningful impact on efforts to improve the health and well-being of us all.