Twin study: Genetics, environment affect different regions of the brain

Twins have long been the subject of studies in the quest to determine the influences of nature vs. nurture. An earlier study, published in the journal Nature Genetics in May 2015, examined more than half a century of research collected on 14.5 million pairs of twins and concluded that the nature versus nurture debate is a draw; both have nearly identical influences on a person's traits and diseases. But we still didn't know specifically how nature and environment can affect our brains.

Now, researchers at Osaka University Graduate School of Medicine in Japan have begun to focus in on just that. In their study of 40 monozygotic (identical) and 18 dizygotic (fraternal) twin pairs, ages 30 or older, they used positron emission tomography (PET) scans with the radiopharmaceutical 2-deoxy-2-F-18-fluoro-D-glucose (FDG) targeting regional cerebral glucose metabolism. Eighteen control pairs matched genetically unrelated individuals of the same age and gender as the twins in the study.

Jun Hatazawa, MD, PhD, corresponding author of the study, explains, "Glucose is an essential fuel for brain energy metabolism as well as oxygen. Functional activation of neurons is normally associated with increases in the local cerebral glucose utilization and blood flow."

They evaluated the F-18 FDG uptake in each cerebral lobe for the identical and fraternal twins as well as the controls. By comparing differences, they could estimate the genetic and environmental contributions.

Hatazawa notes that previous studies have revealed strong genetic influence on the volume of frontal gray matter, whereas this study shows that frontal glucose metabolism is preferentially influenced by environmental factors. Knowing which areas of the brain are more influenced by the environment will help with understanding particular neurological and psychiatric disorders.

He states, "The frontal lobes of monozygotic twins are anatomically identical, but they are metabolically and functionally different under environmental influences. This twin-imaging research can be applied to amyloid imaging in Alzheimer's disease and neurotransmitter-receptor imaging in psychiatric disorders where genetic, epigenetic and environmental influences remain unknown. In future twin studies, we may be able to identify specific environmental risk factors."