Home BiologyFascinating Facts the World Knows Thanks to Twin Studies
BiologyBy Trista -

Fascinating Facts the World Knows Thanks to Twin Studies
Obesity is a disease that occurs when a person’s body accumulates and stores excessive amounts of body fat. Shutterstock

9. A twin study suggested that genetics contribute to 40 to 70 percent of obesity. 

The modernization of our society has contributed to higher rates of obesity through an environment that promotes increased calorie intake and decreased physical activity. It was discovered that more than 50 genes are strongly associated with obesity. While changes in the environment have significantly increased obesity rates over the last 20 years, the presence or absence of genetic factors protect us from or predispose us to obesity. Most commonly, obese individuals have multiple genes that predispose them to gain excess weight. One gene is the fat mass and obesity-associated gene (FTO) found in 43 percent of the population. In the presence of food, those with this particular gene may have challenges limiting their caloric intake. The presence of the FTO gene in combination with other genes can cause increased hunger levels, increased caloric intake, reduced control overeating, and an increased tendency to store body fat.

The classic twin study completed in 1990 looked at the importance of genes for body-fat storage. A dozen lean young male twins were housed and overfed by 1,000 calories a day for three months to do this. Although every participant was heavier by the end of the experiment, the weight gained ranged from nine pounds to 29 pounds. Weight gain within pairs was much more similar than weight gain between different twin pairs. The twins in each pair tended to gain weight in the same places, whether in the abdomen or thighs. This similarity among twins suggests that genetics play a role in the likelihood of obesity and where body fat will be stored. Understanding your family history can help you better understand your risk for obesity or obesity-related conditions. While your genes might predispose you to obesity, it does not have to be your destiny. 

Fascinating Facts the World Knows Thanks to Twin Studies
While in the womb, the brain is changing more rapidly during this time compared to any other time in development. Shutterstock

8. Twin studies have been conducted to show that the environment in the womb sets the tone for your future health. 

It has long been suggested that a mother’s stress during her pregnancy can impact the brain of her developing child. Twin studies have long been used to estimate the unique contributions of genetic and environmental influences on variation in human traits. The prenatal environment is a specific and crucial environmental influence on many human characteristics. Slow growth in utero may be associated with increased allocation of nutrients during development and may result in accelerated weight gain during childhood. Many factors can contribute to the environment in the womb. These include the mother’s age and how many pregnancies she has had.

Beyond these factors, fetal development can be further impaired by poor placental function or maternal disease. An altered long-term risk of illness is initially induced by the fetus’s adaptive responses to the mother’s cues about her health or physical state. Fetal responses can include metabolism changes, hormone production, and tissue sensitivity to hormones that can later affect various organs’ development. The effects of subsequent environmental exposures during infancy, childhood, and adult life may be influenced by these past exposures and may condition the disease’s risk later on in life. The twin studies have helped researchers understand the impacts of lifestyle factors such as diet and stress on our health and how these are possibly passed down through the generations.

Fascinating Facts the World Knows Thanks to Twin Studies
There has been significant research that has examined the influence of our inherited biology on alcohol intoxication. Shutterstock

7. Twin studies have revealed that our genetics play a role in how severe our hangover is. 

Genes interact with environmental factors to influence how much we drink and our susceptibility to becoming dependent on alcohol. Researchers utilized twin studies to assist in untangling the contribution of genetic and environmental factors for a given behavior. To be accurate, researchers looked at the differences in hangover experiences in fraternal and identical twins. Identical twins share all of their genes, and fraternal twins only share 50 percent of their genes, so any differences are assumed to result from genes rather than the environment.  The first study was conducted in 1972, where twins were asked questions to understand their hangover experiences better.

The results indicated that the experience of hangovers is exponentially influenced by genes, with unshared environmental factors accounting for the rest of the variation. A second study was conducted to examine genetic influences on several measures of an alcohol hangover, including frequency, resistance, and susceptibility. This study showed that genetic factors accounted for 45 percent of the difference in hangover frequency in males and 40 percent in females. Our genes might contribute to our ability to drink alcohol without falling victim to a terrible hangover. However, these studies cannot identify which specific genes contribute to the risk of a hangover. The likelihood of identical twins getting hangovers were much more similar in comparison to fraternal twins. This determination revealed that genetics play a decisive role in the chances of having a hangover. 

Fascinating Facts the World Knows Thanks to Twin Studies
Although our genes impact many factors, we cannot ignore that our environment also influences our genes. Shutterstock

6. Researchers have learned that our environment influences genes through twin studies. 

Twin studies have played a critical role in understanding phenotypic heritability. Furthermore, these now offer an opportunity to study epigenetic variation. Epigenetics can be more specifically defined as cellular modifications that can be heritable and modified by the environment. Studies of twins have been critical to distinguish the contribution of genetic factors to numerous complex traits. Twin studies in epigenetics have the potential to address two questions. The two questions include the extent to which epigenetic changes are heritable and how much variation there is in epigenetic heritability across the genome. Identical twins are traditionally referred to as genetically identical. Therefore, any phenotypic differences within identical twin pairs are attributed to environmental factors.

Epigenetic modifications control which genes are essentially switched on and off in a particular cell or tissue. It can be altered by many environmental factors, including diet, exercise, and smoking. Researchers looked at the epigenome of 79 pairs of identical twins. One individual had rheumatoid arthritis and the other was healthy to study if epigenetics was disrupted in rheumatoid arthritis. Although identical twins have identical genomes, they have different epigenomes. The epigenomes’ changes were uncovered to be in genes involved in pathways within a cell that controls cells’ reaction to stress. Cellular stress could have been caused by many factors, including environmental exposures such as smoking. The changes in the DNA methylation can alter how the immune cells react to stress, further sensitizing them and causing an increased immune activity. This heightened sensitivity consequently leads to the progression of the disease. 

Fascinating Facts the World Knows Thanks to Twin Studies
Despite identical twins having the same genome, both twins can have different diseases at different times. Shutterstock

5. Twin studies have helped to identify the genetic and epigenetic risk of breast cancer.

Through the study of twin pairs, researchers have identified which gene increases the risk of breast cancer. Epigenetic marks help to send chemical signals to DNA to tell it to switch on or off. The epigenetic marks can vary from one twin to the next. One research team was able to identify the epigenetic change in the twin who will develop breast cancer even though the other will not. The research group studied DNA methylation levels, which is the best known epigenetic mark, in the blood of 36 pairs of twins diagnosed with breast cancer or healthy. Over half a million pieces of the genome were analyzed in each twin and compared to one another. 

What was uncovered was that women who have developed breast tumors showed a pathological gain of methylation in the DOK7 gene. This epigenetic alteration is associated with an increased risk of breast cancer detected in the sick twin a few years before the clinical diagnosis. The next step in understanding the whole situation is knowing the exact function of the DOK7 gene. It is thought to be a regulator of tyrosine kinases, an antitumor drug target already used to treat breast cancer. If DOK7 performs this function, new studies to test drugs with tumor chemopreventive effects in breast cancer could be planned in the future. 

Fascinating Facts the World Knows Thanks to Twin Studies
Contrary to popular belief that eating disorders are only a result of societal pressures, it has since been revealed that there is a strong genetic component. Shutterstock

4. Twin studies are a helpful tool in behavioral genetics and understanding the complexity of eating disorders. 

By studying twins, researchers can vary family environments and differ in genetic makeup. By comparing twins, scientists can better understand the roles of a shared environment, the impact of genetics, and possible unique environments that influence behavioral traits. Research findings from twin studies on eating disorders have found significant genetic components, including behaviors and attitudes associated with clinical eating pathology. One twin study investigated the ‘thin-ideal internalization’ to determine if genetic factors make individuals more susceptible to this outside pressure than others. Sets of twins were studied and evaluated. When one twin has a disease, the other twin’s chances of having it is called the concordance rate. 

The results showed that identical pairs had a closer level of a thin idealization than fraternal twin pairs. The concordance rate for identical twins was 59 percent compared to only 11 percent for fraternal twins. The exciting findings allowed researchers to determine that genetics play a significant role in this area. It is suspected that several susceptibility genes can contribute to an individual’s risk of an eating disorder. The search for specific genetic factors is still underway. 

Fascinating Facts the World Knows Thanks to Twin Studies
Like most human behavior, intelligence is a complex trait that is influenced by genetic and environmental factors. Shutterstock

3. Intelligence can be challenging to study because it is measured and defined in different ways. According to twin studies, intelligence is in your genes. 

Most of the definitions of intelligence include the ability to learn from experiences and adapt to changing environments. Elements of intelligence include the ability to plan, reason, solve problems, and think critically. Many studies rely on a measure of intelligence called the intelligence quotient, or IQ. Researchers have conducted many studies to look for genes that influence intelligence. Many look at the similarities and differences in IQ within families. These studies suggest that genetic factors contribute to about 50 percent of the difference in intelligence among individuals.

By studying both identical and fraternal twins, researchers found that certain brain regions were highly heritable. That included language areas and the frontal region, which plays a large role in cognition. These specific areas showed a 95 to 100 percent correlation between one twin and the other in identical twins. The frontal structure appears to be highly influenced by genes. Fraternal twins were near identical in the language areas but were less similar in other areas. The studies suggest that the environment, their own experiences, and what they learned in life play a negligible role in shaping their intelligence. 

Fascinating Facts the World Knows Thanks to Twin Studies
While mathematics and reading ability are known to run in families, the complex system of genes affecting these traits is largely unknown. Shutterstock

2. Up to 75 percent of differences in children’s abilities in math, reading, and spelling could be due to genetic differences. 

Twins and unrelated children were tested for reading comprehension and fluency. They then answered mathematics questions based on the national curriculum. The information collected as a result of these tests was combined with DNA data and showed a substantial overlap in the genetic variants that influence mathematics and reading. First, the similarities of thousands of twins were reviewed, and measured their tiny differences in DNA. Similar collections of subtle DNA differences are essential for math and reading. 

However, it would be best if you also were mindful that our life experiences are crucial in making us better at one or the other. That is the complex combination of nature and nurture as we grow up to shape whom we become. Although the study does not point to specific genes, it does suggest that genetics influence complex traits such as learning abilities. Children differ genetically in how easy or difficult they find learning. Furthermore, it is crucial not only to recognize but respect these individual differences. Even though the twin studies found such strong genetic influences does not mean anything can be done to assist if a child finds learning difficult. It may just mean that more effort is needed from schools, parents, and teachers to help bring the child up to speed.

Fascinating Facts the World Knows Thanks to Twin Studies
Numerous twin studies have been conducted in an attempt to clear the importance of genes in sexual orientation. Shutterstock

1. Through recent twin studies, researchers have been able to conclude that sexual orientation is genetically influenced.

Some people claim that sexual orientation is a choice or that being gay is a conscious decision individuals make. To determine the role of genetics, if any, in sexual orientation, researchers compared identical twins to fraternal twins. The 2001 review concluded that almost all identical twins were increasingly more likely to share a sexual orientation. That means that they are both either gay or straight compared to fraternal twins, who are genetically less close. These findings suggest that genes do play a factor in a person’s sexual orientation

Other studies have indicated that biological effects, including hormone exposure in the womb, contribute to shaping sexual orientation. These studies support that the differences in the central nervous system exist between heterosexual and homosexual individuals and that the differences are possibly related to early factors in brain development. There are also findings of physiological differences such as different inner ear shapes between homosexual and heterosexual women that contribute to the idea that biological effects play a role. These studies have been able to debunk the myth that sexual orientation is merely a choice. Instead, it relies heavily on genetic factors. 

Sources:

https://www.ranker.com/list/twin-study-findings/katherine-ripley?ref=browse_list&l=1

https://earthsky.org/human-world/5-discoveries-twin-studies

 

Advertisement