Double Take: What Twin Studies in Scientific and Medical Research Tell Us
Twins are an intriguing phenomenon due to their relative rarity. While not as uncommon as a lightning strike, the 0.4% chance of conceiving twins naturally makes them a subject of fascination and scientific inquiry.
Twins come in two varieties: monozygotic (identical) and dizygotic (fraternal). Identical twins emerge from a single fertilized egg that splits into two, while fraternal twins result from two separate eggs fertilized by different sperm cells. Fraternal twins can be of different sexes and as similar or dissimilar in appearance as any other non-twin siblings.
Identical twins present opportunities for scientific and medical research that may yield knowledge beneficial both to twins and to the wider population alike. Let’s consider some of what we’ve learned through twin studies and related research.
Outcomes of Twin Studies in Scientific and Medical Research
Twin DNA Is Not Identical
Until recently, the scientific community believed that identical twins share 100% of their DNA. This theory has since been debunked, and recent studies suggest that in approximately 15% of identical twin cases, one twin may have significant genetic mutations (differences) compared to the other.
These differences, which begin in the womb, explain the subtle physical variations in identical twins that become more pronounced over time. Fraternal twins share about 50% of the same DNA, which is on par with what non-twin siblings share.
Twins’ Health Prognoses Differ
Since twins do not invariably have 100% identical DNA, they won’t necessarily develop the same diseases or conditions over their lifetimes. Equipped with this knowledge, medical personnel can advise a nonaffected twin to be alert and undergo testing for any conditions or diseases their twin may have but not to consider such issues a certainty.
Environmental Factors May Play a Significant Role in Twin Health
Twin studies have also helped shed light on the age-old nature vs. nurture debate. Twins who are raised in different environments and who have different habits (e.g., diet, exercise and smoking) can provide valuable information about their health through medical research. In many cases, these studies have shown that lifestyle factors outweigh genetic predispositions in determining overall health.
An Australian study of female twins, for example, provided compelling evidence of smoking’s detrimental effects. In pairs where one twin was a heavy smoker, that individual faced double the risk of bone fractures and a significantly higher rate of osteoporosis.
Identical Twins Aren’t Necessarily Identical at Birth
Even identical twins can have significant differences at birth. The timing and location of an egg splitting in the uterus can lead to birth weight variations of greater than 20%, potentially placing the smaller of the two twins at higher risk for poor health outcomes.
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Sources:
https://www.nature.com/articles/s41562-023-01609-6
https://pmc.ncbi.nlm.nih.gov/articles/PMC4919929/
https://www.cambridge.org/core/journals/twin-research-and-human-genetics/article/value-of-twins-for-health-and-medical-research-a-third-of-a-century-of-progress/7D16B5947FE5A97981355F2A6DFE43EF
https://theconversation.com/5-things-research-from-twins-taught-us-about-health-behaviour-and-what-makes-us-unique-172145
