What is Turner syndrome and how does it occur?
One of the most common genetic disorders affecting females (estimated to be present 1 in 2,000 live female births), Turner syndrome occurs when one of the two X chromosomes is missing or at least only partially present.
This condition can be seen in all cells or just in some (where other cells are the conventional and correctly occurring double X chromosomal expression in females). This genetic error is a random occurrence and not an inherited condition. The karyotype in the diagnosis of TS MUST be obtained postnatally to confirm the diagnosis.
Turner syndrome has been linked to a wide variety of physical issues, such as impaired or delayed growth resulting in short stature for a given age, infertility, and problems with heart and kidneys. Cognitive and emotional symptoms are also observed, as are abilities visual and spatial perception.
In fact, the broad array of symptoms seen in Turner syndrome are such that it may be overlooked in diagnosis because these symptoms are seen in many other conditions. The range of age at diagnosis varies greatly – from before birth to decades later in life, although the average age for identifying Turner syndrome has decreased in recent decades.
Lack of federal funding for neonatal screening does not mean that individual states are unable to make the informed decision to add TS to their individual state’s newborn screen. There is currently a voluntary study in North Carolina that provides free health tests to newborn babies—including screening for TS. Learn more here.
How are female twins affected by Turner syndrome?
Image source: inviTRA
Turner syndrome is caused by a random error in cell division during egg or sperm formation, or very early after fertilization.
Because fraternal twins come from two separate eggs and two separate sperm, the chromosomal error can easily occur in one embryo only leading one twin to have Turner syndrome, while the other twin has no effects at all.
For identical twins originating from one egg but splitting into two embryos, there still may be chromosomal mosaicism or cell division errors that affect one twin differently, if those differences arise after the embryo splits. Rare but documented cases exist where only one identical twin has Turner syndrome
Challenges in the Relationship of Twin Sisters
For cases where one twin is affected by Turner syndrome and the other is not, there may be physical, mental, and emotional differences that can present as a challenge throughout the lifespan. Currently there is little research on how an errant genetic variation between twins can affect relationships, developmental milestones, and overall well-being, but it is important for parents to be aware of these differences that may arise and consult with their care team on the best course of action to ensure each twin receives the care and support they need.
Although much has been discovered and learned since Turner syndrome was identified in 1938, the effect on the ongoing lives and relationships of affected and unaffected twin sisters warrants further study.
If you are a twin with Turner syndrome, we would love to share your story to help bring awareness to these circumstances!
Written by Robert Burleson, Edited and designed by Gerely Caba, TSF Blog Coordinator.
© Turner Syndrome Foundation, 2026
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I am a mom of monochorionic (identical) twins. They were supposed to be two male babies, but a genetic mutation affecting one of those babies caused a mosaic TS and the baby developed as female (XY, X).
I always have issues speaking about our stories, as anyone who has a little knowledge about twins is always speaking about how “impossible” it is to have identical twins who are a boy and a girl.
But it is! I am raising them!
There is an important need to spread more information about this topic.