Other Sex Chromosome Differences | Prenatal Screening Ontario

What are sex chromosome differences?

Each of us is usually born with two sex chromosomes. If you are a female, you were likely born with two X chromosomes. If you are a male, you were likely born with a X chromosome and a Y chromosome.

A sex chromosome difference is when there are extra or missing sex chromosomes. About 1 in 500 to 1 in 1000 people are born with a sex chromosome difference. It is possible for someone to have a sex chromosome difference and not be aware of it, so these conditions may be more common than we think.

Most of the time, sex chromosome differences happen by chance and are not passed down from other family members.

What will a sex chromosome difference mean for the baby?

People with a sex chromosome difference have a greater chance to develop certain health issues and other challenges that also happen in the general population. Some people with sex chromosome differences do not have any of these issues, while others have several. These include:

Differences in height - taller or shorter than average.
Reaching milestones later than other children (such as learning how to talk or walk).
Learning difficulties. Most individuals with a sex chromosome difference do not have an intellectual disability, but may have certain problems with learning.
Puberty happening later than expected.
Fertility challenges.
Problems with the ability to plan, focus attention, and juggle multiple tasks.
Anxiety and other mental health challenges.

There is effective treatment and support to help people with a sex chromosome difference if needed. Many people go on to lead full and healthy lives.

For information on Turner Syndrome (Monosomy X), click on the link below

Learn more about Turner syndrome

Common sex chromosome differences

There are different types of sex chromosome differences. Symptoms vary a lot from one person to another even when they have the same type of sex chromosome difference. People with sex chromosome differences have their own strengths and challenges, like anyone else. There is no way to know how a sex chromosome difference will impact someone until they grow and develop.

Trisomy X syndrome (47, XXX)

Trisomy X syndrome (also called Triple X syndrome) happens in females. Females with trisomy X syndrome have an extra X chromosome.

Girls with trisomy X syndrome generally have no physical differences, except that they might be taller than average. Other girls may have more symptoms, including:

Learning challenges (like problems with reading)
Reaching some milestones later than other children (like learning how to walk, and talk).

Most women with trisomy X syndrome are able to go through puberty at the expected time, and can get pregnant.

Klinefelter syndrome (47, XXY)

Klinefelter syndrome happens in males. Males with Klinefelter syndrome have an extra X chromosome.

Boys might have certain physical differences, such as:

Being taller than average.
Having extra breast tissue.
Less muscle mass.
Less body and facial hair.
Small testes.

Most males with Klinefelter syndrome have normal intelligence. There is an increased chance for:

Learning disabilities (like problems with reading and writing).
Attention-deficit hyperactivity disorder (ADHD).
Reaching milestones later than other children (like taking longer to crawl, walk and speak).
Difficulties with social interaction.

Most men with Klinefelter syndrome make little or no sperm. Fertility treatments can help some men have children, either by using their own sperm or donor sperm. Men with Klinefelter syndrome also have a higher chance to develop:

Diabetes mellitus.
Thyroid problems.
Osteoporosis (weak bones).
Autoimmune diseases.

Some of the symptoms happen because less testosterone (a male hormone) is made. Treatment involves giving male hormones to help with some of these symptoms. This treatment will not improve infertility.

Since symptoms can be mild, boys are often not diagnosed with Klinefelter syndrome until puberty or when they are trying to have children. Many men will go on their entire lives without knowing they have this diagnosis.

XYY syndrome (47, XYY)

XYY syndrome happens in males. Males with XYY syndrome have an extra Y chromosome.

Boys with XYY syndrome generally have no physical differences, except that they are often taller than average.

Most males with XYY syndrome have normal intelligence but there is an increased chance of learning issues (especially problems with talking and reading) and social interaction difficulties. Some boys with XYY syndrome have behavioral issues.

Men with XYY syndrome are expected to go through puberty at the expected time, and to have their own children.

How can sex chromosome differences be detected during pregnancy?

With the use of prenatal screening and diagnostic testing, sex chromosome differences are found during pregnancy more frequently now than ever before.

| Prenatal screening tests

If you choose to have Non-Invasive Prenatal Testing (NIPT), this prenatal screening test can tell you the chance for having a baby with a sex chromosome difference. The test is covered by OHIP in certain situations. Keep in mind that screening for sex chromosome differences is not as accurate as it is for other conditions. Many people who get a "high risk" result through NIPT do not end up having a baby with a sex chromosome difference.

Sex chromosome differences cannot be screened through other OHIP-funded prenatal screening tests - enhanced First Trimester Screening (eFTS) or Second Trimester Screening (STS).

| Diagnostic testing

The only way to know for sure if the baby has a sex chromosome difference is through a diagnostic test. This testing can be done by looking at cells from the placenta (chorionic villus sampling) or from the fluid around the baby (amniocentesis).

Diagnostic testing is not generally done during the pregnancy unless there are signs that the baby might have a chromosome difference or another genetic concern. Sometimes, a diagnostic test is done as a follow up to a "high risk" NIPT result. Other times, it is done for an unrelated reason and a sex chromosome difference is found by chance.

Some people do not wish to have diagnostic testing during the pregnancy. In that case, diagnostic testing can be done after birth by getting some blood from the umbilical cord, or through a regular blood draw from the baby.

| Ultrasound

Generally, a baby with a sex chromosome difference will not show any signs on ultrasounds. Turner syndrome (Monosomy X) is an exception. Turner syndrome can have serious implications for the baby's health before birth, and certain signs on ultrasound can be seen.

More information

You can get more information from other medical and advocacy organizations. These can be helpful resources when looking for a range of views on living with sex chromosome differences and when you are looking for information in other languages.

The Association for X and Y Chromosome Variations (AXYS)
Rare Diseases - XYY syndrome, Trisomy X, XXY syndrome
Mayo Clinic - Klinefelter syndrome, Trisomy X (available in English, Arabic, Spanish and Simplified Chinese)
Living with XXY