Twin Study Finds Genetics and Environment Affect Different Brain Regions

A recent study, reported in the March issue of The Journal of Nuclear Medicine, found evidence that genetic influence on cerebral glucose metabolism played a major role in the bilateral parietal lobes and the left temporal lobe of the human brain, while environmental influences after birth dominated in other regions.

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.

Image shows twin women.

Twins have long been the subject of studies in the quest to determine the influences of nature vs. nurture. Image is for illustrative purposes only.

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.”

About this neuroscience research

Funding: Funding was provided by KAKENHI grants-in-aid for scientific research, Osaka Medical Research Foundation for Intractable Disease.

Source: Laurie Callahan – SNM
Image Credit: Image is in the public domain.
Original Research: Abstract for “Genetic and Environmental Influences on Regional Brain Uptake of 2-deoxy-2-18F-fluoro-D-glucose: a PET Study in Monozygotic and Dizygotic Twins” by hinichiro Watanabe, Hiroki Kato, Eku Shimosegawa, and Jun Hatazawa in Journal of Nuclear Medicine. Published online November 19 2015 doi:10.2967/jnumed.115.164004


Abstract

Genetic and Environmental Influences on Regional Brain Uptake of 2-deoxy-2-18F-fluoro-D-glucose: a PET Study in Monozygotic and Dizygotic Twins

Genetic or environmental influences on cerebral glucose metabolism are unknown. We attempted to reveal these influences in elderly twins by means of 18F-FDG PET.

Methods: 18F-FDG uptake was studied in 40 monozygotic and 18 dizygotic volunteer twin pairs aged 30 y or over. We also created 18 control pairs by pairing age- and sex-matched genetically unrelated subjects from dizygotic and monozygotic pairs. SUV images of the brain were reconstructed and analyzed by voxel-based statistical analysis with automated region-of-interest setting. The 18F-FDG uptake in each cerebral lobe was semiquantified by taking a ratio of SUVmean in each region of interest to whole-brain SUVaverage. We calculated an intraclass correlation coefficient of SUV ratio in each region of interest for monozygotic and dizygotic pairs. By comparing differences in coefficients between monozygotic and dizygotic pairs, genetic and environmental contributions were estimated.

Results: The intraclass correlation coefficient in monozygotic pairs was significantly higher than that in dizygotic pairs in the parietal lobes bilaterally (P < 0.001) and in the left temporal lobe (P < 0.05) but was not significantly different in other lobes.

Conclusion: The present study indicated that in the right and left parietal lobes and left temporal lobe, cerebral glucose metabolism is influenced more by genetics than by environment, whereas in other brain regions the influence of environment is dominant.

“Genetic and Environmental Influences on Regional Brain Uptake of 2-deoxy-2-18F-fluoro-D-glucose: a PET Study in Monozygotic and Dizygotic Twins” by hinichiro Watanabe, Hiroki Kato, Eku Shimosegawa, and Jun Hatazawa in Journal of Nuclear Medicine. Published online November 19 2015 doi:10.2967/jnumed.115.164004

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