Genetics and Twins: the TWIN-E Project

Risk for mental illnesses like depression, anxiety, attention deficit disorder and schizophrenia is determined by our genetics and environment. Twin studies compare identical to non-identical twins to determine how much is determined by genetics and how much by environment. Neuroscience is helping us understand that genes and environment impact behaviors, both in healthy individuals and in patients with mental illness, by modifying the way our brain systems function. That means that a second way that twin information can be valuable is to investigate how genes versus environment impacts measures of these brain systems. We have undertaken a series of interlinked studies to investigate how gene-environment interactions affect healthy behavior, the heritability of these behaviors and their role in predicting mental health outcomes.

The studies in this research program have gathered information from both non-twin and twin samples to understand the role of genetics and environment in behaviors relevant to mental health. The aims of these studies are:

(1) To study non-twin healthy people to understand how genetics map onto brain systems and the behavior these brain systems relate to. We investigate both emotional and cognitive behaviors. We have focused on single nucleotide polymorphisms (SNPs) and other common genetic variants known to modulate neurotransmitters and hormones in the brain. We have also investigated how environmental stressors, especially early life trauma, interact with these SNPs to impact brain function.

(2) To study twins to determine the level of heritability of different aspects of brain systems, including brain structure and function measured using MRI and EEG, autonomic function, cognition and behavior. By comparing identical twins (or monozygotic, MZ) who share 100% of their genetic make-up to non-identical (or dizygotic, DZ) twins who share only 50%, we are able to derive the relative percentage contribution of genes and environment to each measure.

To address the first aim we drew on the BRAINnet Database and to address the second aim we have undertaken the TWIN-E Study, a national study of twins. Both datasets have the same standardized set of MRI, EEG, autonomic, cognitive and behavioral measures.

The study involves the testing of over 1,600 healthy adult twins from 18 to 65 years of European ancestry. The study protocol involves three phases. All participants are asked to complete some web-based tests and to provide a saliva sample to assess their DNA. Up to 25% of participants are then given the opportunity to participate in some further brain tests in our labs located in Adelaide or Westmead Hospital. These tests involve completing some simple computer tasks during an EEG recording and/or an MRI brain scan. Following a 12-month period, participants are re-contacted and asked to repeat the web-based tests again in their own time. Twin pairs are then provided the opportunity to participate in a randomized controlled trial where each twin out of a twin pair are randomly allocated to a treatment or waitlist control group to test the effects of brain training on mental health over a 30-day period.