Because XXY males do not really appear different from other males and because they may not have any or have mild symptoms, XXY males often don't know they have KS.1,2
In other cases, males with KS may have mild or severe symptoms. Whether or not a male with KS has visible symptoms depends on many factors, including how much testosterone his body makes, if he is mosaic (with both XY and XXY cells), and his age when the condition is diagnosed and treated.
KS symptoms fall into these main categories:
Many physical symptoms of KS result from low testosterone levels in the body. The degree of symptoms differs based on the amount of testosterone needed for a specific age or developmental stage and the amount of testosterone the body makes or has available.
During the first few years of life, when the need for testosterone is low, most XXY males do not show any obvious differences from typical male infants and young boys. Some may have slightly weaker muscles, meaning they might sit up, crawl, and walk slightly later than average. For example, on average, baby boys with KS do not start walking until age 18 months.3
After age 5 years, when compared to typically developing boys, boys with KS may be slightly:
Puberty for boys with KS usually starts normally. But because their bodies make less testosterone than non-KS boys, their pubertal development may be disrupted or slow. In addition to being tall, KS boys may have:
An adult male with KS may have these features:
In some cases, breast growth can be permanent, and about 10% of XXY males need breast-reduction surgery.6
Most males with KS have normal intelligence quotients (IQs)7,8 and successfully complete education at all levels. (IQ is a frequently used intelligence measure, but does not include emotional, creative, or other types of intelligence.) Between 25% and 85% of all males with KS have some kind of learning or language-related problem, which makes it more likely that they will need some extra help in school. Without this help or intervention, KS males might fall behind their classmates as schoolwork becomes harder.
KS males may experience some of the following learning and language-related challenges:9
By adulthood, most males with KS learn to speak and converse normally, although they may have a harder time doing work that involves extensive reading and writing.
Many of the social and behavioral symptoms in KS may result from the language and learning difficulties. For instance, boys with KS who have language difficulties might hold back socially and could use help building social relationships.
Boys with KS, compared to typically developing boys, tend to be:
In the teenage years, boys with KS may feel their differences more strongly. As a result, these teen boys are at higher risk of depression, substance abuse, and behavioral disorders. Some teens might withdraw, feel sad, or act out their frustration and anger.
As adults, most men with KS have lives similar to those of men without KS. They successfully complete high school, college, and other levels of education. They have successful and meaningful careers and professions. They have friends and families.
Contrary to research findings published several decades ago, males with KS are no more likely to have serious psychiatric disorders or to get into trouble with the law.10
Males with poly-X Klinefelter syndrome have more than one extra X chromosome, so their symptoms might be more pronounced than in males with KS. In childhood, they may also have seizures, crossed eyes, constipation, and recurrent ear infections. Poly-KS males might also show slight differences in other physical features.
Some common additional symptoms for several poly-X Klinefelter syndromes are listed below.
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