Swyer Syndrome (XY Gonadal Dysgenesis)

What is Swyer syndrome?

Swyer syndrome is when a person has XY (male) chromosomes and functional female genitalia (vulva). While XY chromosomes usually result in the development of a penis and scrotum, people with Swyer syndrome develop a vagina, uterus and fallopian tubes.

People with Swyer syndrome don’t have sex glands (ovaries or testicles). Instead, they have functionless scar tissue (called streak gonads). This means they won’t go through puberty unless they have hormone replacement therapy. They also won’t become pregnant naturally but can conceive through egg donation.

Another name for Swyer syndrome is XY gonadal dysgenesis. “Gonadal” refers to sex glands and “dysgenesis” means “abnormal development.” Swyer syndrome falls under the intersex umbrella. Healthcare providers categorize it as a disorder of sexual development (DSD).

Because of their outer appearance, people with Swyer syndrome are assigned female at birth (AFAB). Some align with this gender identity. Others may explore different gender identities or choose to have gender affirmation surgery.

How common is Swyer syndrome?

Swyer syndrome is a rare condition that affects about 1 in 80,000 births.

What are the symptoms of Swyer syndrome?

Most people don’t notice symptoms of Swyer syndrome until adolescence, when puberty usually begins. Signs and symptoms can be different for everyone, but may include:

• Underdeveloped breasts.
• Lack of menstrual periods (amenorrhea).
• Taller than peers.
• Hair doesn’t grow in pubic or axillary (armpits or legs) areas.

What causes Swyer syndrome?

Experts don’t always know exactly what causes Swyer syndrome. But based on existing research, they think it’s due to mutations of genes responsible for sex differentiation. Simply stated, any change to a gene that plays a role in testicle development could result in Swyer syndrome.

Some people inherit Swyer syndrome from a biological parent (who may or may not know they have a gene mutation). Others develop the condition spontaneously, meaning it’s a new gene mutation that happened for unknown reasons.

In 15% to 20% of people with Swyer syndrome, the condition happens because of a mutation (change) of the SRY (sex-determining region Y) gene. Geneticists believe the SRY gene helps transform undifferentiated tissue (tissue without a specific purpose) into testicles. A change in the SRY gene keeps this from happening, so testicles never develop.

Changes to the following genes can also cause Swyer syndrome:

• MAP3K1.
• DHH.
• NR5A1.

What are the complications of Swyer syndrome?

Complications of Swyer syndrome include:

• Gonadal tumor: About 30% of people with Swyer syndrome will develop a tumor that starts in the gonadal streaks (scar tissues) that form where ovaries typically are. The most common type of tumor among those with Swyer syndrome is a gonadoblastoma. While gonadoblastoma is benign (noncancerous), healthcare providers consider it a precursor to malignant (cancerous) tumors. For this reason, healthcare providers usually recommend surgery to remove the gonadal streaks as a preventive measure.
• Osteoporosis: Untreated, Swyer syndrome can also cause your bones to weaken, eventually resulting in osteoporosis. Hormone replacement therapy can help prevent bone thinning and loss.

How is Swyer syndrome diagnosed?

Sometimes, healthcare providers can identify Swyer syndrome before or at birth. But many people don’t know they have it until later when they don’t go through puberty as expected.

During an office visit, a healthcare provider will do a physical examination and ask about your medical history. They may also order imaging or lab tests to learn more about your anatomy or chromosomal makeup, including:

• Karyotype testing.
• Genetic testing.
• Pelvic ultrasound.
• MRI (magnetic resonance imaging).

How is Swyer syndrome treated?

As Swyer syndrome can’t be cured, the main goals of treatment are managing unwanted symptoms, keeping your bones strong and reducing your cancer risk. To do this, your healthcare provider may recommend:

• Preventive surgery to remove gonadal streaks.
• Hormone replacement therapy to induce menstruation and breast enlargement, and to prevent osteoporosis.

Can Swyer syndrome be prevented?

Swyer syndrome is a genetic condition, so there’s nothing you can do to prevent it.

What should I expect if my child has Swyer syndrome?

Puberty is never an easy time. And for kids with Swyer syndrome, it's probably the first time they’re learning that their bodies are different from their peers.

Your child will likely have a lot of feelings. Talk openly with them. Seek the help of a counselor to help them navigate these complex emotions.

What’s the life expectancy for someone with Swyer syndrome?

People with Swyer syndrome have the same life expectancy as people without the condition. With treatment, it shouldn’t affect your or your child’s lifespan in any way.

When should I see my healthcare provider?

If you’re AFAB and you haven’t started your period by age 16, schedule an appointment with a healthcare provider.

If you’re a parent and your child has delayed puberty, talk to your child’s pediatrician. They can monitor their development and let you know whether they need treatment.

What questions should I ask my doctor?

If you received a Swyer syndrome diagnosis, here are some questions you may want to ask your healthcare provider:

• Do you know which gene mutation caused the condition?
• When do I need to start hormone replacement therapy?
• Will I or my child need surgery? If so, when?
• Should my family have genetic testing?
• What resources do you recommend?