twins: picture: pexels
Imagine discovering that a person carries a twin within themselves—a hidden, undeveloped sibling that shares space, blood flow, or even physical features. This rare and mysterious phenomenon, known as parasitic twinning, unveils some of the most extraordinary facets of human development.
Parasitic twins occur when one twin ceases to develop fully in the womb, becoming physically dependent on the other for survival. Often a mystery to those who encounter it, parasitic twinning challenges our understanding of life itself, sparking curiosity and offering insights into genetics, and the human body’s adaptability. Dive into the science behind parasitic twins, where reality meets the edge of medical marvels and mysteries.
In medical terms, the Cleveland Clinic states that “A parasitic twin is a rare condition that happens when a conjoined twin stops developing. The parasitic twin never fully develops but stays attached to its twin, who continues to develop until birth. A parasitic twin happens early in embryonic development, so its organs or limbs can be nearly unrecognisable.”
The clinic continues to explain that the developed twin, also known as the “dominant or autositic twin”, ends up being born with additional limbs, organs, or tissue from its parasitic twin. The dominant twin is said to require medical care after birth since they are very susceptible to health issues.
According to WebMD, two theories suggest parasitic twins occur, fission theory, where the fertilised egg splits into two parts, and fusion theory, where the egg separates but both parts interact, resulting in conjoined twins.
The above source claims that researchers are also studying the impact of the Sonic Hedgehog protein (SHH) on parasitic twin development, as abnormal levels can lead to fused eyes, legs, and feet. “The SHH protein family is a fundamental compound involved in the development and maintenance of cells.”
Healthlinementions the different types of this condition and how it manifests in terms of location.
- Cephalopagus: back of the head
- Craniopagus parasiticus: cranium
- Cpigastric: upper abdomen, above the stomach
- Ischiopagus: pelvis
- Omphalopagus: abdomen
- Parapagus: trunk
- Pygomelia: limbs attached to buttocks; might appear as a pseudo-tail
- Pyopagus: lower spine
- Rachipagus: back
- Thoracopagus: upper chest
Also see: Understanding the difference between a gynaecologist and a midwife
