Overview
47,XYY syndrome, also known as XYY syndrome or Jacob syndrome, is a chromosomal condition that occurs when a male is born with an extra Y chromosome, resulting in a 47,XYY karyotype instead of the typical 46,XY. This additional Y chromosome arises from a nondisjunction event during paternal meiosis II or from a postzygotic mitotic error. The condition is one of the most common sex chromosome aneuploidies in males. Many individuals with 47,XYY syndrome are never diagnosed because the features can be subtle and highly variable. The condition primarily affects growth and development. Males with 47,XYY syndrome tend to be taller than average, often exceeding the 75th percentile for height by adolescence. Neurodevelopmental features are common and may include speech and language delays, learning difficulties (particularly in reading), attention deficit hyperactivity disorder (ADHD), and mild delays in motor development. Some individuals may experience behavioral challenges, including difficulties with emotional regulation and social interaction, though the severity varies widely. Intelligence is generally within the normal range, though IQ may be slightly lower than unaffected siblings. Fertility is typically normal, as most men with 47,XYY syndrome produce normal sperm, although some may experience reduced fertility. Other features that have been reported include tremor, increased risk of asthma, and mild hypotonia in childhood. There is no cure for 47,XYY syndrome, as it is a chromosomal condition present from conception. Management is supportive and tailored to the individual's specific needs. Early intervention services, including speech therapy, occupational therapy, educational support, and behavioral therapy, can significantly improve outcomes. Hormonal evaluation may be warranted if there are concerns about pubertal development or fertility. With appropriate support, most individuals with 47,XYY syndrome lead healthy, productive lives.
Also known as:
Clinical phenotype terms— hover any for plain English:
Sporadic
Usually appears on its own, not inherited from a parent
Variable
Can begin at different ages, from infancy through adulthood
FDA & Trial Timeline
2 eventsUniversity Hospital, Bordeaux — NA
University of Colorado, Denver
Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.
Treatments
No FDA-approved treatments are currently listed for 47,XYY syndrome.
1 clinical trialare actively recruiting — trials can provide access to cutting-edge therapies.
View clinical trials →Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to 47,XYY syndrome.
Community
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Start the conversation →Latest news about 47,XYY syndrome
Disease timeline:
New recruiting trial: Generating Advancements Through Longitudinal Analysis in X and Y Variations (GALAXY)
A new clinical trial is recruiting patients for 47,XYY syndrome
New recruiting trial: CACP: Study on Camptodactyly - Arthropathy - Coxa Vara - Pericarditis (CACP) Syndrome
A new clinical trial is recruiting patients for 47,XYY syndrome
New recruiting trial: Contribution of Anti-platelet Antibodies Identified With MAIPA Assay in the Demonstration of the Auto-immune Character of a Thrombocytopenia at Diagnosis
A new clinical trial is recruiting patients for 47,XYY syndrome
New recruiting trial: The eXtroardinarY Babies Study: Natural History of Health and Neurodevelopment in Infants and Young Children With Sex Chromosome Trisomy
A new clinical trial is recruiting patients for 47,XYY syndrome
Caregiver Resources
NORD Caregiver Resources
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Mental Health Support
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Common questions about 47,XYY syndrome
What is 47,XYY syndrome?
47,XYY syndrome, also known as XYY syndrome or Jacob syndrome, is a chromosomal condition that occurs when a male is born with an extra Y chromosome, resulting in a 47,XYY karyotype instead of the typical 46,XY. This additional Y chromosome arises from a nondisjunction event during paternal meiosis II or from a postzygotic mitotic error. The condition is one of the most common sex chromosome aneuploidies in males. Many individuals with 47,XYY syndrome are never diagnosed because the features can be subtle and highly variable. The condition primarily affects growth and development. Males with
How is 47,XYY syndrome inherited?
47,XYY syndrome follows a sporadic inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
Are there clinical trials for 47,XYY syndrome?
Yes — 1 recruiting clinical trial is currently listed for 47,XYY syndrome on UniteRare. See the clinical trials section on this page for phase, sponsor, and site details sourced from ClinicalTrials.gov.
Which specialists treat 47,XYY syndrome?
4 specialists and care centers treating 47,XYY syndrome are listed on UniteRare, sourced from ClinicalTrials.gov principal investigators, published research, and the NPPES NPI registry.