This is also known as the XXY condition.  It is a term used to describe males who have an extra X chromosome in most of their cells.  The normal or usual chromosome pattern in males is XY.

All men with Klinefelter syndrome have the extra X chromosome; however, not every XXY male has all of the symptoms associated with the syndrome.  For this reason, it is common to use the term XXY male or XXY condition to describe the symptoms.

This condition is one of the most common chromosome abnormalities in humans according to scientists.  The rate is about one of every 500 males who have an extra X chromosome.  Many do not have the symptoms.  Not all males have the same symptoms or to the same degree.  The symptoms depend upon:

•    How many XXY cells a man has
•    How much testosterone is in his body
•    His age when the condition is diagnosed

This condition can affect three main areas of development which are:

•    Physical development
•    Language development
•    Social development

Physical Development

Male babies with XXY condition may have:

•    Weak muscles
•    Reduced strength
•    They may sit up, crawl and walk later than other infants
•    After age four, XXY males tend to be taller and may have less muscle control and coordination than other boys their age

At puberty, they:

•    Often don’t make as much testosterone as other boys, which can lead to a taller, less muscular body, less facial and body hair and broader hips than other boys

As teens, XXY males may have:

•    larger breasts
•    weaker bones
•    a lower energy level than other boys

At adulthood, XXY males:

•    look similar to males without the condition, although they might be taller
•    they are more likely than other men to have certain health problems like autoimmune disorders, breast cancer, vein diseases, osteoporosis and tooth decay
•    they can have normal sex lives, but they usually make little or no sperm
•    between 95 percent and 99 percent of males are infertile because their bodies don’t make a lot of sperm

Language Development

As boys, between 25 percent and 85 percent have some kind of language problem such as:

•    learning to talk late
•    trouble using language to express thoughts and needs
•    problems reading
•    trouble processing what they hear

As adults, XXY males may:

•    have a harder time doing work that involves reading and writing
•    Most hold jobs and have successful careers

Social Development

As babies, XXY males tend to be:

•    Quiet and undemanding

As they get older, they are:

•    Quieter
•    Less-confident
•    Less active
•    More helpful and obedient than other boys

As teens, XXY males tend to be:

•    Quiet and shy
•    May struggle in school and sports
•    May have more trouble fitting in with other kids

As adults, they:

•    Live lives similar to men without the condition
•    Have friends, families and normal social relationships

Are there any treatments for the XXY condition?

This is a chromosome pattern that cannot be changed.  However, the symptoms can be treated in a variety of ways that include:

•    Educational treatments
•    Therapeutic options such as physical, speech, occupational, behavioral, mental health and family therapists can help reduce or eliminate some of the symptoms with poor muscle tone, speech or language problems, or low self-confidence
•    Medical treatments such as testosterone replacement therapy to get their testosterone levels into normal range to help them develop bigger muscles deepen the voice and grow facial and body hair.  This treatment often starts at puberty.  Fertility treatment is also available to help them father children.

What is an important factor for all types of treatment?

•    Start it as early in life as possible.

For more information:

You can receive a free 31-page booklet online or in print entitled:  “Understanding Klinefelter Syndrome:  A Guide for XXY Males and Their Families,” from:

National Institute of Child Health and Human Development, NIH, DHHS. (1997)
Understanding Klinefelter Syndrome:  A Gjuide for XXY Males and Their Families (97-3202)
Washington, DC:  U.S. Government Printing Office

Source:  National Institute of Child Health and Human Development

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