A 35-year-old woman in Brazil was discovered to possess XY chromosomes – typically associated with males – exclusively in her blood, while the rest of her body maintained a standard female XX chromosomal profile. The unusual finding emerged after she experienced a miscarriage and sought genetic testing to determine if an underlying condition was responsible.
The Diagnostic Puzzle
Standard karyotype analysis (a chromosomal profile) revealed a 46,XY pattern in her blood cells, a result normally seen in men. Further investigation, including tests on skin cells, confirmed a 46,XX karyotype in other tissues. This discrepancy pointed to a rare condition called chimerism, where an individual carries at least two genetically distinct cell populations. Chimerism can occur through medical intervention (like transfusions or transplants) but can also develop naturally, particularly in twins sharing the same placenta.
The Twin Connection
The woman’s case was traced back to feto-fetal transfusion during her development with a twin brother. This means blood cells were exchanged in the womb due to intertwined blood vessels, giving her XY chromosomes in her blood while her other tissues remained XX. Genetic analysis of her brother and parents confirmed the match, revealing that he carried the same XY genetic variants as those found in her blood.
Implications for Reproduction
Notably, the patient had no other physical or hormonal abnormalities. She developed normally, experienced regular menstruation, and had no previous health complications. More importantly, after a precautionary progesterone regimen following another pregnancy, she successfully gave birth to a healthy child. This case is unique because it demonstrates that complete blood chimerism does not necessarily disrupt reproductive ability.
Undiagnosed Cases Likely Remain
The patient’s condition was only detected because of a miscarriage-triggered genetic test, which is not standard practice. This suggests that many individuals may carry hidden chromosomal anomalies without ever knowing, and blood chimerism is likely underreported. The authors note that other chromosomal variations, like extra sex chromosomes, also go undetected in many cases.
“There was a transfusion process that we call feto-fetal transfusion… At some point, the veins and arteries of the two children became intertwined in the umbilical cord.” — Dr. Gustavo Arantes Rosa Maciel
This case is the first documented instance of a woman with complete blood chimerism who otherwise displayed typical female traits, had no health issues, and was able to conceive successfully. It underscores how little is known about the prevalence and impact of chimerism in humans.
