What You Should Know About Mosaic Turner Syndrome

What is mosaic Turner syndrome?

Chromosomes are what carry genetic information (also called DNA) from each cell throughout the human body. Each person is born with 23 pairs of chromosomes — 46 total — including one pair of sex chromosomes, X and Y.

Turner syndrome affects people who were assigned female at birth. While people assigned female at birth typically have two X chromosomes (XX), people with Turner syndrome have just one X chromosome.

Because so much genetic information is missing at such an early stage of development, Turner syndrome can cause a variety of medical and developmental concerns, including failure of the ovaries to develop, heart defects, and short height.

There are two main types of Turner syndrome:

• Monosomy X Turner syndrome: This type is defined as a complete loss of the second X chromosome.
• Mosaic Turner syndrome: This type is defined as a partial loss of the second X chromosome.

In general, symptoms for people with mosaic Turner syndrome tend to be less severe than symptoms for people with complete Turner syndrome. This is because the number of cells that are affected by the missing or deficient X chromosome is fewer with mosaicism.

Some cells contain the usual two XX chromosomes and, therefore, do not contribute to health issues.

What are the symptoms of mosaic Turner syndrome?

Symptoms may vary greatly between people with mosaic Turner syndrome. Some people may not even realize they have this condition until puberty or later in life.

Symptoms may include:

• short height
• amenorrhea, or missed menstrual periods
• infertility from ovary issues
• congenital heart disease, like bicuspid aortic valve
• difficulties with spatial awareness
• hearing issues from repeat ear infections

In addition to these symptoms, a person with mosaic Turner syndrome may have certain physical characteristics, including:

• low hairline on the back of the head
• narrow upturned fingernails
• webbing skin on the neck
• broad “shield” chest with wide-set nipples
• puffy hands and feet (lymphedema)
• pigmented moles (nevi)

Again, these symptoms may be milder than people experience with complete Turner syndrome. A 2018 study revealed that people with the mosaic (partial) form tended to be closer to average height with fewer reproductive and heart issues.

What does “intersex” mean?

During the diagnostic process, you may hear the term “intersex.”

Medically, the term simply means a person has biological traits of more than one sex. It may mean a person has external characteristics of one sex but internal reproductive anatomy of another sex. For example, a person may be born with a penis and ovaries.

In the case of Turner syndrome, the term “intersex” relates to genetic material. While the external reproductive anatomy may appear to be female, some or all of the pair of sex chromosomes, which typically determine the physical characteristics of reproductive anatomy, may be missing the second X chromosome. For this reason, Turner syndrome is considered an “intersex condition.”

However, people with mosaic Turner syndrome are likely to be assigned female at birth and may never display any intersex characteristics outside of changes to their second X chromosome in some cells of their body.

“Intersex” also has a meaning in a broader social context. The “I” in LGBTQIA+ is for “intersex.” People with intersex traits may identify as male or female rather than as intersex. Some people may be unaware they have intersex traits, like changes in their chromosomes or internal organs.

Language matters

In the past, the term “hermaphrodite” was used instead of “intersex.” This term is now outdated and considered very offensive.

What causes mosaic Turner syndrome?

Turner syndrome is rare. It affects roughly 1 in every 2,000 to 2,500 female births across the globe.

The mosaic form of this condition is caused by a partial loss of the second X chromosome. The one-chromosome form is caused by a complete loss of the second X chromosome.

A 2013 study found that between 30% and 40% of people with Turner syndrome have the mosaic form.

What causes the loss of this second sex chromosome isn’t fully understood yet. Researchers believe it may happen at random during reproduction. It could occur soon after the sperm meets the egg or early in fetal development.

Turner syndrome does not appear to be genetically inherited. This means it does not run in families.

How is mosaic Turner syndrome diagnosed?

Diagnosis is often made after a baby is born, in either childhood or adolescence. The physical features of infants with Turner syndrome may be recognizable at birth or emerge during infancy.

If your child shows signs after birth, their pediatrician may order tests, such as:

• Blood tests to examine the chromosomes: Tests of chromosomes like karyotyping are used to identify whether any chromosomes or chromosomal material is missing or altered.
• MRI: MRIs produce images that may be used to detect issues with the heart, liver, or kidneys.
• Cardiac testing: Tests like echocardiogram may be used to evaluate heart issues.
• Ear, nose, and throat (ENT) exams: These tests may help detect hearing issues.
• Other tests: Tests such as thyroid function tests, liver function tests, and high blood pressure screening may be used to help diagnose conditions that affect organs or systems in the body.

Prenatal diagnosis (during pregnancy)

In some cases, a doctor may diagnose Turner syndrome before a baby is born through prenatal genetic testing. In particular, karyotyping may be performed by sampling a mother’s blood, bone marrow, or other tissue that can identify any chromosomal abnormalities in the fetus.

Ultrasound may also help doctors diagnose Turner syndrome during pregnancy. Some babies may have lymphedema (swelling) or issues with the kidneys or the heart that are visible on prenatal ultrasounds.

Is there a treatment for mosaic Turner syndrome?

There’s no cure for Turner syndrome. Instead, treatment aims to address whatever signs or symptoms a person with Turner syndrome is experiencing. Treatment varies by the person and their needs.

A 2018 study involving people with mosaic Turner syndrome found that treatment may not be necessary — particularly in cases when the syndrome is found by chance.

This means some people may have mosaic Turner syndrome that doesn’t cause symptoms or health issues, so there’s no need for any treatment.

Otherwise, treatment options may include:

• Growth hormone therapy: Growth hormone therapy can help address short stature.
• Estrogen or progesterone hormone therapy: Hormone therapy, like estrogen or progesterone therapy, may help address sexual development.
• Psychological support: Psychological support, like cognitive behavioral therapy and other types of counseling, can help address depression, stress, or learning issues people with Turner syndrome may experience.

What’s the outlook for people who have mosaic Turner syndrome?

Symptoms of mosaic Turner syndrome tend to be milder than those of complete Turner syndrome. As a result, people with this condition may lead relatively healthy lives.

Early diagnosis and treatment can help with growth and development issues before and during puberty. That said, not all people with mosaic Turner syndrome will have delays in their development. Or if they do, these issues may only be minor.

Frequently asked questions

Do people with mosaic turner syndrome have difficulties with fertility?

Most people with mosaic Turner have either reduced fertility or infertility. In vitro fertilization may help address fertility issues.

However, people with mosaic Turner syndrome who do become pregnant are at risk of blood pressure–related complications, which can lead to premature birth or fetal growth restriction.

Pregnancy in people with mosaic Turner syndrome is also associated with an increased risk of maternal complications, including heart conditions like aortic dissection and aortic rupture.

Is there a relationship between mosaic Turner syndrome and autism?

Researchers are exploring the potential link between Turner syndrome and autism. In one British study from 2018, the rate of autism in people with Turner syndrome was 21% compared with the U.K. rate in females of 0.3%.

Bottom line

Mosaic Turner syndrome is a developmental abnormality involving the sex chromosomes. Turner syndrome results when one of the X chromosomes (sex chromosomes) is missing or partially missing following conception.

Treatment can help with a person’s specific health issues but may not be necessary if symptoms are mild.

People with this condition may have a range of health and development issues, but they generally may lead healthy lives.

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