For so many of us, the essence of happiness lies in the taste of a piece of good chocolate. However, my friend doesn’t much care for it. Could such almost criminal dislike of chocolate be explained by genetics? Indeed, scientists have been puzzled by the origin of complex human traits ranging from personal behavior to the occurrence of diseases since early civilisation. Twins can be valuable subjects to pull apart and study our inherent and environmentally influenced characteristics.
Identical or monozygotic twins share almost all of their genes. In contrast, dizygotic or fraternal twins share about 50 percent of their genes like any other sibling. Studying twins is the only real way of finding out how human traits are inherited. Victorian scientist Francis Galton was one of the first to note the value of twins for studying hereditary traits. He was highly interested in the effects of “nature versus nurture”, a term coined by himself. However, his interpretations from twin studies led him to the dark belief that genetic qualities of the human race could be improved by selective breeding, and thus to the rise of “eugenics”. Nowadays, large-scale twin registers serve as a grand platform to study complex traits and diseases. The Swedish twin registry managed by Karolinska Institutet contains extensive information about 85,000 twin pairs and has approximately 30 ongoing research projects.
When astronaut Scott Kelly landed on Earth last March, breaking the US record for the most time spent in space, he also set a landmark for twin studies. Scott and Mark Kelly are identical twins and astronauts, who came up with the idea of an unprecedented experiment to figure out how extended space travel affects the human body. During the study, between 2015 and 2016, Mark was on Earth and Scott was in space. Biological samples were taken from the Kelly brothers before, during and after the space flight, allowing for the most thorough molecular profiling of human beings done by ten research groups. Preliminary results from the study are truly exciting to the scientific community.
“The greatest importance
of the study is to show
that we can do it.”
“Almost everyone is reporting that we see differences”, said Christopher Mason, a geneticist at Weill Cornell Medicine in New York City, in a Nature report. Researchers found that Scott’s telomeres, protective caps at the end of chromosomes, to grow longer during the spaceflight and return to original length after landing on Earth. They discussed that physical activity and special diet might have counteracted the damaging effects of space travel. An independent study including ten astronauts has been initiated by NASA on telomere length to figure out what the results really mean. Mason’s research team reported around 200,000 RNA molecules to be differentially expressed between the twins. A closer look will reveal if a “space gene” was activated during the spaceflight.
The fact that the Kelly brothers are just two people poses a challenge for the scientists to untangle natural variations from real effects of space travel. Despite the limitation of having only one twin pair, the current study generates an enormous amount of new knowledge about the responses of the human body to gravity-free life. Scientific team member Andrew Feinberg said at the NASA Human Research Program’s annual workshop, highlighting the success of ‘omics in science: “The greatest importance of the study is to show that we can do it.” Knowledge obtained from the Kelly study will be of great significance for Mars journey preparations. As a mission to Mars will likely last for three years, it is crucial to understand the challenges that humans may face on the way.
Numerous twin studies have led us to important discoveries. And what about chocolate? You guessed it: Twins helped us to figure out the genetics of taste preferences, too! •