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Disease Information

Summary

48,XXYY syndrome is a chromosomal condition that affects male development. There is a lot of variability in symptoms between people with 48,XXYY syndrome. Almost all affected individuals have developmental delays in infancy and develop decreased testosterone levels (hypogonadism) during adolescence. People with 48,XXYY syndrome are also at risk for other health problems. Adolescents and adults with this condition usually have small testes that do not produce enough testosterone, which is the hormone that directs male sexual development. Without treatment, a shortage of testosterone during puberty can lead to reduced facial and body hair, poor muscle development, low energy levels, and an increased risk of breast enlargement (gynecomastia). Because their testes do not function normally, individuals with 48,XXYY syndrome have difficulty having biological children (a condition called infertility), but they may be able to have children using assisted reproductive technologies. 48,XXYY syndrome can affect other parts of the body as well. Affected individuals are often taller than their peers, with an average adult height of 6 feet, 4 inches (193 cm). They may develop a mild to moderate hand tremor that typically starts in adolescence and may increase with age. Dental problems are frequently seen in people with this condition,  including delayed appearance of the primary (baby) or secondary (adult) teeth, thin tooth enamel, crowded or misaligned teeth, and multiple cavities. Additionally, individuals with 48,XXYY syndrome may have flat feet (pes planus), elbow abnormalities, abnormal fusion of certain bones in the forearm (radioulnar synostosis), allergies, asthma, type 2 diabetes, seizures, congenital heart defects, and an inflammatory condition in the throat (esophagus) called eosinophilic esophagitis. As people with 48,XXYY get older, they may develop a narrowing of the blood vessels in the legs called peripheral vascular disease. Peripheral vascular disease can cause skin ulcers to form. Affected individuals are also at risk of developing a type of clot called a deep vein thrombosis that occurs in the deep veins of the legs. Most individuals with 48,XXYY syndrome have an IQ score that ranges from 60 to 80 and have some degree of difficulty with speech and language development. The development of motor skills such as sitting, standing, and walking may be delayed in some children with 48,XXYY syndrome. They may also have poor coordination. Learning disabilities are very common in people with this disorder, especially in the areas of reading and written expression. People with 48,XXYY typically perform better at tasks focused on math, visual-spatial skills such as puzzles, and memorization of locations or directions. Affected individuals have higher-than-average rates of other neurodevelopmental and behavioral disorders, such as attention-deficit/hyperactivity disorder (ADHD); mood disorders, including anxiety and depression;and autism spectrum disorder, which affects communication and social interaction.

About XXYY syndrome

Many rare diseases have limited information. Currently, GARD aims to provide the following information for this disease:

  • Symptoms:May start to appear at a variety of ages.
  • Cause:This disease is caused by changes to the number or structure of a person’s chromosomes.
  • Organizations:Patient organizations dedicated to this rare disease are available on GARD, or you may contact a GARD Information Specialist for additional information.
  • Categories:Genetic diseases(Genetic diseases affect the DNA, or genetic instructions, which directs how tissues, organs, and body systems function.)Neurological diseases(Neurological diseases affect the brain, spinal cord, cranial nerves, autonomic nerves, or other peripheral nerves.)Endocrine diseases(Endocrine diseases affect hormone production or how the body responds to a specific hormone(s).)Birth defects(Birth defects are structural changes present at birth that can affect almost any part of the body, including how the body looks, works, or both.)Urinary and Reproductive diseases(Urinary and reproductive diseases affect the kidneys, ureters, bladder, urethra, or the reproductive organs.)

Resource(s) for Medical Professionals and Scientists on This Disease:

  • MONDO provides GARD with information for this disease.
  • Orphanet provides GARD with information for this disease.

Resource(s) for Medical Professionals and Scientists on This Disease:

  • MONDO provides GARD with information for this disease.
  • Orphanet provides GARD with information for this disease.

About XXYY syndrome

Many rare diseases have limited information. Currently, GARD aims to provide the following information for this disease:

  • Symptoms:May start to appear at a variety of ages.
  • Cause:This disease is caused by changes to the number or structure of a person’s chromosomes.
  • Organizations:Patient organizations dedicated to this rare disease are available on GARD, or you may contact a GARD Information Specialist for additional information.
  • Categories:Genetic diseases(Genetic diseases affect the DNA, or genetic instructions, which directs how tissues, organs, and body systems function.)Neurological diseases(Neurological diseases affect the brain, spinal cord, cranial nerves, autonomic nerves, or other peripheral nerves.)Endocrine diseases(Endocrine diseases affect hormone production or how the body responds to a specific hormone(s).)Birth defects(Birth defects are structural changes present at birth that can affect almost any part of the body, including how the body looks, works, or both.)Urinary and Reproductive diseases(Urinary and reproductive diseases affect the kidneys, ureters, bladder, urethra, or the reproductive organs.)

Causes

What Causes This Disease?

Genetic Mutations

Changes in your genes (also called variants) cause XXYY syndrome.

Genes are sections of DNA that contains instructions that help the body grow, develop, and function. A genetic variant is a change in your DNA's order. Parents may pass variants to their children, or they may occur randomly. They may result from viruses, environmental factors, such as UV radiation, or a combination of causes.

Most genetic variants do not cause disease. However, some can affect how a gene works and interfere with the body's normal functions. A pathogenic variant is one that causes disease.

If you think you may have this disease, collect your family health history (CDC). It may help you and your medical team to know about family members who have had the disease or similar symptoms and when those symptoms first appeared.

Read more about genetic disorders (NIH MedlinePlus). 

Genetic Mutations

Changes in your genes (also called variants) cause XXYY syndrome.

Genes are sections of DNA that contains instructions that help the body grow, develop, and function. A genetic variant is a change in your DNA's order. Parents may pass variants to their children, or they may occur randomly. They may result from viruses, environmental factors, such as UV radiation, or a combination of causes.

Most genetic variants do not cause disease. However, some can affect how a gene works and interfere with the body's normal functions. A pathogenic variant is one that causes disease.

If you think you may have this disease, collect your family health history (CDC). It may help you and your medical team to know about family members who have had the disease or similar symptoms and when those symptoms first appeared.

Read more about genetic disorders (NIH MedlinePlus). 

Chromosomal Changes

XXYY syndrome is caused by a change in the number of chromosomes a person has, or a change in their structure.  Chromosomes are structures within cells that hold all our genes. People usually have 46 chromosomes; 23 come from the biological mother and 23 come from the biological father. Most of the time, chromosomal changes occur randomly in the sperm or egg, but some changes are known to be passed on from parent to child. Learn more about chromosomal diseases from the National Human Genome Research Institute (NHGRI).

Given the known chromosomal changes for this disease, you may want to ask your health care team if chromosome testing is right for you. Results from chromosome testing can confirm or rule out a suspected chromosomal disease or help determine a person’s chance of passing on a disease. Visit the NHGRI website to learn about microarray technology used in chromosomal testing, understand how a karyotype can be used to determine chromosomal abnormalities, and discover the FISH lab technique used to detect a specific DNA sequence on a chromosome.

When Do Symptoms of XXYY syndrome Begin?

Symptoms of this disease may start to appear at a variety of ages.

The age symptoms may begin to appear differs between diseases. Symptoms may begin in a single age range, or during several age ranges. The symptoms of some diseases may begin at any age. Knowing when symptoms may have appeared can help medical providers find the correct diagnosis.
  1. Prenatal
    Before Birth
  2. Newborn Selected
    Birth-4 weeks
  3. Infant Selected
    1-23 months
  4. Child Selected
    2-11 years
  5. Adolescent Selected
    12-18 years
  6. Adult
    19-65 years
  7. Older Adult
    65+ years
Symptoms may start to appear at a variety of ages.
This information comes from Orphanet

Symptoms

You may have one or more symptoms, and they may be mild or severe. Having some or all of these symptoms does not mean you have this disease. Only a health care provider can diagnose you.

Common

Many people have these, but not everyone.

  • Abnormal speech pattern
  • Abnormal tooth enamel (Abnormal dental enamel morphology)
  • Abnormality of the shoulder (Abnormal shoulder morphology)
  • Absent sperm in semen (Azoospermia)
  • Anxiety
  • Asthma
  • Attention deficit (Attention deficit hyperactivity disorder)
  • Chronic infections of the middle ear (Chronic otitis media)
  • Constipation
  • Cross-eyed (Strabismus)
  • Decreased testicular size
  • Delayed eruption of teeth
  • Dental cavities (Carious teeth)
  • Depression
  • Double-Jointed (Joint hypermobility)
  • Elbow dislocation
  • Enlarged male breast (Gynecomastia)
  • Eye folds (Epicanthus)
  • Feeding difficulties in infancy
  • Flat feet (Pes planus)
  • Flat occiput
  • Fused forearm bones (Radioulnar synostosis)
  • Global developmental delay
  • Hypergonadotropic hypogonadism
  • Increased volume of lower lip (Thick lower lip vermilion)
  • Infertility
  • Intellectual disability
  • Low muscle tone (Hypotonia)
  • Narrow opening between the eyelids (Blepharophimosis)
  • Obesity
  • Open bite
  • Permanent curving of the pinkie finger (Clinodactyly of the 5th finger)
  • Recurrent respiratory infections
  • Tall stature
  • Taurodontia
  • Tremor
  • Upward slanting of the opening between the eyelids (Upslanted palpebral fissure)
  • Wide-set eyes (Hypertelorism)

Uncommon

Some people have these, but most people do not.

  • Abnormal cardiovascular system morphology
  • Acid reflux (Gastroesophageal reflux)
  • Apnea
  • Ataxia
  • Autism
  • Broad jaw
  • Cancer of lymphatic system (Lymphoma)
  • Cleft palate
  • Difficulty articulating speech (Dysarthria)
  • Facial asymmetry
  • Hip dysplasia
  • Inguinal hernia
  • Involuntary, rapid, rhythmic eye movements (Nystagmus)
  • Long face
  • Noninsulin-dependent diabetes (Type II diabetes mellitus)
  • Psychosis
  • Repetitive movements (Motor stereotypy)
  • Scoliosis
  • Seizure
  • Talipes
  • Underdeveloped penis (Hypoplasia of penis)
  • Undescended testes (Cryptorchidism)
  • Ventriculomegaly
This information comes from the Human Phenotype Ontology (HPO)

Navigating Health Care Decisions

On average, it can take more than six years to receive an accurate diagnosis. Many primary care providers (PCPs) may not be familiar with rare diseases, and patients often need to visit multiple specialists or seek second opinions to get answers.

If a diagnosis remains unclear, visiting a multidisciplinary care center or university hospital may help. These centers bring together teams of specialists who can work together to evaluate symptoms and coordinate a diagnosis. This team-based approach is also helpful after a diagnosis, when managing care for rare diseases.

Because only about 5% of rare diseases have FDA-approved treatments, finding the right healthcare team to manage your symptoms and overall health is essential. People living with rare diseases often face challenges such as delayed diagnosis, limited treatment options, and difficulty accessing knowledgeable providers. Building a care team that understands your needs can make a significant difference in your quality of life.

Your Health Care Team

Why is building the right health care team important?

Building the right health care team is key to the diagnosis, treatment, and management of your long-term health journey living with a rare disease. Start by choosing a primary care provider (PCP). Your PCP will be your main point of contact and help coordinate care with other medical professionals. Your PCP may order tests or refer you to specialists. To find a PCP near you, use the Medicare provider search tool and enter your location and “Primary Care Provider.”

Seeing multiple specialists is important for people with rare diseases because these conditions often affect many parts of the body and require care from doctors with different expertise. Most primary care providers may not be familiar with rare diseases, so involving specialists can lead to a more accurate diagnosis and better care. A coordinated team approach ensures that all symptoms are addressed and that care is well-managed. It can also connect patients with the latest research or treatment options.

A PCP that specializes in the care of children is called a pediatrician. Use this tool by the American Academy of Pediatrics to find a pediatrician in your area by inputting your location.

These specialists may help in the diagnosis, management, and treatment of XXYY syndrome:

Neurologists are doctors with specialized training in diagnosing and treating conditions that affect the brain, spinal cord, and nerves. These parts of the nervous system help control how the body moves, feels, and thinks. Neurologists often care for people with seizures, memory problems, muscle weakness, movement disorders, and inherited conditions such as muscular dystrophies. To better understand a person's symptoms, neurologists may use imaging tests that show the brain or spine, or tests that measure the brain’s electrical activity.

You may want to consider bringing a copy of your medical history and a list of any medications to your appointment.

Ask your primary care provider for a referral or use this directory provided by the American Board of Psychiatry and Neurology to find a specialist. 
Geneticists are doctors trained to diagnose and manage conditions caused by genetic changes, birth defects, or metabolic disorders. Metabolic disorders affect how the body makes or uses energy. Geneticists often work alongside genetic counselors to review family history, discuss genetic risks, explain testing options, and interpret genetic test results. They help people understand how inherited conditions may affect them and their families.

You may want to consider bringing a copy of your medical history and a list of any medications to your appointment.

Ask your primary care provider for a referral or use this directory provided by the American College of Medical Genetics and Genomics to find a specialist.
Endocrinologists are doctors trained to diagnose and manage diseases related to hormones. Hormones are chemical messengers that help coordinate many body functions, including metabolism, growth, and reproduction. Endocrinologists commonly treat conditions such as diabetes, thyroid disorders, and certain hormone-related cancers. They also care for people with concerns about growth or sexual development. Treatment options may include medications, hormone replacement therapy, or surgery, depending on the condition.

You may want to consider bringing a copy of your medical history and a list of any medications to your appointment.

Ask your primary care provider for a referral or use this directory provided by the Endocrine Society to find a specialist.
Urologists are doctors with specialized training in diagnosing and treating conditions that affect the urinary system in both males and females, as well as the male reproductive system. They often manage urinary tract infections, kidney stones, bladder control issues, prostate conditions, and cancers involving these organs. Urologists use imaging, lab tests, or procedures to diagnose and guide treatment. Some may specialize in specific areas such as pediatric or cancer-related urology.

You may want to consider bringing a copy of your medical history and a list of any medications to your appointment.

Ask your primary care provider for a referral or use this directory by Medicare to search for a urologist in your area. Search using the keywords “Urology.”

Multidisciplinary Care Centers

Is It Time to Get a Second Opinion or Specialized Evaluation?

If you've visited your PCP, met with specialists, and undergone the recommended tests, but are still searching for a diagnosis, it may be time to visit an academic medical center or, for pediatric patients, a children's hospital. Academic medical centers and children's hospitals, often called multidisciplinary care centers, typically bring together specialists from different fields to work together on complex cases like rare diseases.

Multidisciplinary care centers may offer more coordinated care and be involved in clinical research, which may help reduce the time to diagnosis and provide access to emerging diagnostic tools. Specialists at these centers may have a deeper understanding of rare diseases and serve as a resource when you'd like a second opinion, particularly when test results or treatment plans are not delivering expected results.

Find hospitals that may partner with medical schools and programs in your area. 

Children’s hospitals and large teaching hospitals may also offer dedicated specialists and programs for pediatric patients with undiagnosed or rare diseases. These programs bring pediatric experts together in one place and may provide more coordinated care for your child.

Search for children's or university hospitals in your area.

Rare Disease Experts

How can you find a rare disease expert?

If a diagnosis, care management, or treatment plan remains unclear despite extensive efforts by your PCP and specialists, it may be time to find a rare disease expert for your disease, if available. A rare disease expert is a medical provider that has knowledge or training on specific rare disease(s), but there may only be a few experts in your state, region, or country. Rare disease experts may work at large research or teaching hospitals, sometimes called centers of excellence. Centers of Excellence commit to sharing knowledge and best practices that can lead to improved care and treatment for individuals living with a rare disease. 

You can also contact a GARD Information Specialist for help finding experts, centers of excellence, or clinics that focus on your disease.
You can ask your care providers for help finding an expert or use directory tools to search for experts near you. The following organization(s) may maintain a list of experts or expert centers for people living with XXYY syndrome:

Find Your Community

How can patient organizations help?

Patient organizations can help patients and families connect. They build public awareness of the disease and are a driving force behind research to improve patients' lives. They may offer online and in-person resources to help people live well with their disease. Many collaborate with medical experts and researchers.

Services of patient organizations differ, but may include:

  • Ways to connect to others and share personal stories
  • Easy-to-read information
  • Up-to-date treatment and research information
  • Patient registries
  • Lists of specialists or specialty centers
  • Financial aid and travel resources


Please note: GARD provides organizations for informational purposes only and not as an endorsement of their services. Contact a GARD Information Specialist for more information on organizations that may be dedicated to this disease. Please contact an organization directly if you have questions about the information or resources it provides.


View GARD's criteria for including patient organizations, which can be found under the FAQs on our About GARD page. Request an update or to have your organization added to GARD. 

Patient Organizations

3 Organizations

Association for X and Y Chromosome Variations

People With

XXYY syndrome

Helpful Links
Country

United States

Chromodiversity Foundation

People With

XXYY syndrome

Country

Chromosome Disorder Outreach

People With

Chromosome disorders

Country

United States

OrganizationPeople WithHelpful LinksCountry
Association for X and Y Chromosome VariationsXXYY syndromeList of Experts
Research Registry		United States
Chromodiversity FoundationXXYY syndrome
Chromosome Disorder OutreachChromosome disordersUnited States

Participate in Research

Clinical studies are a part of clinical research and play an important role in medical advances for rare diseases. Through clinical studies, researchers may ultimately uncover better ways to treat, prevent, diagnose, and understand human diseases.

What Are Clinical Studies?

Clinical studies are medical research involving people as participants. There are two main types of clinical studies:

  1. Clinical trials determine if a new test or treatment for a disease is effective and safe by comparing groups receiving different tests/treatments.
  2. Observational studies involve recording changes over time among a specific group of people in their natural settings.

Learn more about clinical trials from this National Institutes of Health webpage.

Why Participate in Clinical Studies?

People participate in clinical trials for many reasons. People with a disease may participate to receive the newest possible treatment and additional care from clinical study staff as well as to help others living with the same or a similar disease. Healthy volunteers may participate to help others and to contribute to moving science forward.

To find the right clinical study we recommend you consult your doctors, other trusted medical professionals, and patient organizations. Additionally, you can use ClinicalTrials.gov to search for clinical studies by disease, terms, or location.

What if There Are No Available Clinical Studies?

ResearchMatch helps connect people interested in research studies  with researchers from top medical centers across the United States. Anyone from the U.S. can register with this free program funded by NIH. Researchers from participating institutions use the database to search for and invite patients or healthy volunteers who meet their study criteria to participate.

Why may you want to consider joining the All of Us Research Program?

The All of Us Research Program is inviting 1 million people from all backgrounds across the U.S. to help build one of the most diverse health databases in history. Researchers will use the data to learn how our biology, lifestyle, and environment affect health. This may one day help them find ways to treat and prevent diseases.

ClinicalTrials.gov, an affiliate of NIH, provides current information on clinical research studies in the United States and abroad. Talk to a trusted doctor before choosing to participate in any clinical study. We recommend checking this site often and searching for studies with related terms/synonyms to improve results.
Search ClinicalTrials.gov for this disease.
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Contact a GARD Information Specialist if you need help finding more information on this rare disease or available clinical studies. Please note that GARD cannot enroll individuals in clinical studies.
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Sources & References

Last Updated: September 2026