Klinefelter syndrome (KS) occurs in some men who have more than one X chromosome (XXY).
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Males usually inherit a single X chromosome from their mother and a single Y chromosome from their father. Males with KS get at least 1 extra X chromosome.
Women over age 35 may have a slightly increased chance of having a child with KS. There are no other known risk factors for this disorder.
Most men with KS do not have symptoms. When KS does develop, it usually goes undetected until puberty or sometimes much later.
Babies may have lower birth weight, or slower muscle and motor development.
Children or adults may have: Social and learning disabilitiesEnlarged breastsInability to produce spermSmall, firm testesSmall penisAbnormal body proportions, such as long legs or short trunkTallness with extra long arms and legsPersonality impairmentAttention deficit hyperactivity disorder
(ADHD)Speech and language problems—Children with KS often learn to speak later than other children do. They may have a difficult time reading and writing.Normal to borderline IQLack of facial and body hairDiminished sex drive or sexual dysfunction
Men with KS have an increased risk of: Type 2 diabetesBreast cancerLung cancerCardiovascular diseaseLung diseaseOsteoporosisHypothyroidismDental problemsLeg ulcers
A test called a karyotype is used to diagnose KS. In the case of KS, there are usually 47 chromosomes rather than the normal 46.
Many men with XXY do not know they have the condition. Diagnosis of KS may be found incidentally. For example:
In baby boys with
or very small penis
In boys who have persistent learning problemsIn adolescent boys with delayed puberty or excessive breast development
In adult men who have fertility
Treatment of KS includes:
The main treatment is testosterone . When boys with KS are 10-12 years old, their hormone levels are checked yearly. If testosterone levels are low, then treatment may be helpful. Men diagnosed may also benefit from taking the hormone. However, testosterone cannot reverse infertility.
The benefits of testosterone include: Increased strengthMore muscular, male appearanceGrowth of facial and body hairBetter self-esteemModulation of moodIncreased energyIncreased ability to concentrateGreater sex driveImproved bone density
This therapy should begin in early childhood to avoid social and school learning problems. Treatment may involve: Speech therapySpecial education servicesExtra support and help with learning from parents and teachersSocial skills training and psychological counseling
There are no current guidelines to prevent KS. If you are pregnant, talk to your doctor about prenatal care and screening tests.
Tell me about 47, XXY. Klinefelter Syndrome and Associates website. Available at:
http://www.genetic.org/Knowledge/WhatAreXYChromosomeVariations/Tellmeabout47,XXY.aspx. Accessed June 6, 2016.
Klinefelter syndrome (KS): Overview. National Institute of Child Health and Human Development website. Available at:
Updated October 25, 2013. Accessed June 6, 2016.
Last reviewed June 2016 by Kari Kassir, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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