Vanishing twin syndrome is a phenomenon that occurs during multiple pregnancies, where one of the fetuses disappears early in gestation. This usually happens when one embryo fails to develop or is reabsorbed by the surviving twin, the placenta, or the mother’s body. The presence of DNA from the vanished twin in the surviving individual leads to questions about how long this genetic material can persist and be detected.
The Phenomenon of Vanishing Twin Syndrome
Vanishing twin syndrome describes the loss of one twin or multiple embryos during pregnancy, typically in the first trimester. With widespread early ultrasound use, this phenomenon is estimated to occur in approximately 20% to 30% of twin pregnancies. The lost fetal tissue is absorbed, giving the appearance of the twin “vanishing.”
This reabsorption can lead to chimerism or microchimerism in the surviving individual. Chimerism refers to the presence of cells from two or more genetically distinct individuals within a single organism. The surviving twin can acquire some of the deceased twin’s cells, effectively carrying an extra set of DNA.
Where Vanishing Twin DNA Can Be Found
DNA from a vanished twin, existing as microchimeric cells, can be detected in various tissues and bodily fluids of the surviving individual. These cells, originating from the absorbed twin, can integrate into different parts of the body. They have been identified in circulating blood cells, including granulocytes, lymphocytes, and monocytes.
Beyond the bloodstream, these microchimeric cells can also reside in solid organs and tissues. Research indicates their presence in the bone marrow, liver, kidney, spleen, lungs, heart, and skin. Additionally, DNA from a vanished twin can sometimes be found in cheek swabs and hair follicles, indicating widespread distribution throughout the body.
Factors Influencing DNA Persistence and Detection
DNA from a vanished twin can persist in the surviving individual for many years, often for decades. This persistence is attributed to the transferred cells’ stem cell-like properties, allowing them to integrate and multiply within the recipient’s tissues. These cells can establish long-lasting lineages within the body, contributing to their long-term presence.
The detectability of this DNA depends on several factors, including the initial amount of genetic material exchanged and the specific tissues where the cells engraft. The sensitivity of DNA testing methods also plays a crucial role. While older methods like STR-PCR have a sensitivity of approximately 1% to 5%, newer technologies such as quantitative PCR (qPCR) and Next-Generation Sequencing (NGS) can detect much lower concentrations. Although some DNA might persist indefinitely, its concentration can decrease over time, potentially falling below the detection limits of standard tests.
Implications for Genetic and Health Testing
The presence of DNA from a vanished twin can have significant implications for genetic and health testing. In paternity and maternity testing, the existence of a second DNA profile can lead to ambiguous or confusing results, occasionally causing individuals to appear unrelated to their biological children. Instances have been reported where a parent’s DNA from a vanished twin caused unexpected outcomes in paternity disputes.
For forensic analysis, chimerism presents a challenge, as DNA samples from different tissues of the same individual might yield varying genetic profiles. This can complicate identification and lead to misinterpretations of genetic evidence. In prenatal screening, particularly non-invasive prenatal testing (NIPT), the DNA from a vanished twin can cause false positive or false negative results for chromosomal abnormalities or sex determination. Delaying NIPT until later in pregnancy, such as after 14 weeks, may improve accuracy as the contaminating DNA may have faded.