The three-headed 'Chimera' is one of Greek mythology’s most fantastical creatures. She had a lion’s front—legs, chest, and a mane-framed head—while her midsection was that of a she-goat, with a second goat’s head rising from her back that could breathe fire. Her hindquarters were dragon-like, ending in a serpent’s tail tipped with a snake’s head. This blend of lion, goat, and serpent made the Chimera an enduring mythical icon.
Today, 'Chimera' describes anything made of parts that don’t usually belong together, a term used in fields from art and architecture to cybersecurity and genetics. Natural human chimeras also exist—people who carry more than one genetically distinct cell line from different zygotes. Recently, medical literature reported the case of a woman who carried her twin brother’s DNA in her blood, yet showed typical female traits and could become pregnant. She never knew she was a 'chimera' until age 35, when she had a miscarriage.
The case, published in Gene Reports, involved this patient from Brazil who arrived at the hospital after losing a pregnancy at seven weeks. When her gynaecologist ran chromosomal tests to check for possible causes, a startling detail emerged: her blood cells had a 46,XY profile—typically male. Confused, doctors tested other tissues and discovered her skin cells were 46,XX, the usual female pattern.
A physical examination showed typical female traits and a healthy reproductive system. It was observed that her sexual development was also normal. The patient had a twin brother, and when doctors tested samples from him and their parents, they found that the genetic variants in the brother’s XY blood cells matched the ones present in her blood.
Doctors eventually concluded she carried two sets of DNA—her own and her twin brother’s—absorbed early in development. Medical science refers to this as feto-fetal transfusion, which can occur when the veins and arteries of twins become intertwined in the umbilical cord.
The case became the first instance of complete blood chimerism. It was observed that though rare, this phenomenon is possible and can appear without any sexual or reproductive abnormalities.
Also read
- Surgeon operates from 5,000 km away: How Mumbai patients were operated on from another country
- FACT CHECK: Can rabies REALLY spread through infected cow's milk?
- New Year, new skin: The everyday mistakes you need to avoid in 2026
- From Paresh Rawal's urine therapy to Tamannaah's skincare myths: Top 5 viral health claims in 2025
It was also observed that the woman’s body created a brand-new immune 'ID tag' by mixing her own DNA with her absorbed twin brother’s DNA. This showed that when twins share blood cells very early in the womb, the immune system can learn to accept the “foreign” cells forever, instead of attacking them.
Most previously documented human chimeras with mixed sex chromosomes showed significant physical or reproductive issues. This patient did not. In fact, 11 months after the miscarriage, she conceived again. With progesterone support during pregnancy, she reportedly delivered a healthy boy—a child for whom she is both mother and, genetically speaking, an uncle.
