Overview
Fertility is usually normal.
Older ideas that it causes aggression are not true.
Symptoms
Common signs:
- XYY diagnosis
Less common
- Learning or speech delays
- Tall height
- Low muscle tone
When to get medical care
Call 911This isn't an emergency by itself. Call 911 for trouble breathing, chest pain, or fainting.
Get care todaySeizures, a fall in skills, or big behavior changes.
See a doctor soonLearning or attention concerns.
Causes
An extra Y from a random cell division.
Does it spread or run in families?
- It isn't contagious. You can't catch it from someone else.
Diagnosis
A genetic test confirms it.
Tests
Tests, if needed:
- Chromosome test (karyotype):
Treatment
Early support helps.
Self-care
- Early intervention
- School evaluation
- Keep regular checkups
- Encourage sports and activities he enjoys
Prevention
It can't be prevented.
- There is no known way to prevent it. Early checkups help find it sooner.
Which doctor treats this
- Start with your primary care provider (family doctor or internist).
- They may send you to a medical geneticist (genetics doctor).
Children, pregnancy, and older adults
- Teens: Some may need help with attention or social skills.
Outlook
Most live healthy, full lives.
Life expectancy is normal.
Getting ready for your visit
Bring a list of your symptoms and medicines.
Questions to ask
- Should we tell school?
Research studies
Research studies test new ways to find and treat health problems. Some are looking for volunteers. Talk with your doctor before joining one.
Search ClinicalTrials.gov for studies on XYY syndrome (47,XYY)
Sources
Last updated 2026-11-12.