Genetics Northern California

Klinefelter Syndrome

Klinefelter syndrome is a relatively common chromosome abnormality that affects only males. This condition can affect growth, learning, and fertility, but symptoms are not always easily recognized. It occurs in approximately 1 out of every 600 male births. That means about one boy with Klinefelter Syndrome is born every day in California.

Boys and men with Klinefelter Syndrome tend to be taller than expected as compared to other members of their families and otherwise look normal.

In childhood, many boys with Klinefelter syndrome have developmental delays and learning disabilities, but mental retardation is not generally associated with the syndrome.  Intelligence usually falls in the average range (IQ = 80-120) with slight differences compared to other family members (typically about 10-15 points lower). Boys with Klinefelter syndrome are at increased risk for learning disabilities in language, motor, and reading skills. These disabilities are similar to those experienced by approximately 15% of children in the general population and are managed in the same way. The language difficulties experienced by these boys may explain the behavioral tendency towards shyness, unassertiveness, and immaturity.

Klinefelter syndrome can impact the production of male hormones, but does not affect gender identification or sexual identification. Because of reduced levels of hormones, boys with this condition may experience delayed puberty or find that the physical changes of puberty are less noticeable. They may have less facial and body hair, decreased muscle development, and a smaller testicle size. Although slight breast enlargement can be part of normal male puberty, Klinefelter syndrome sometimes causes more noticeable breast development.  As adults, about 95% of men with this condition are infertile, despite normal sexual function. 

Our genes are instructions or blueprints that make each human being unique. Our genes are packaged into chromosomes, and human beings usually have 46 chromosomes. Chromosomes come in pairs, and we inherit one of each pair from our mother and the other from our father. One pair is called the sex chromosomes. They are called that because they determine the gender of the individual. Normally, females have two X chromosomes, and males have one X and one Y chromosome. Boys with Klinefelter Syndrome have an extra X chromosome. That means that instead of having one X chromosome and one Y chromosome, these boys have two X chromosomes and one Y. The Y chromosome provides the instructions needed for male development, so people with Klinefelter Syndrome are always male.

Sometimes, instead of having two sex chromosomes, babies are born with a different number or different combination of sex chromosomes. This happens completely by chance in pregnancies of women from all ages and ethnic backgrounds. Sex chromosome abnormalities are some of the most common chromosome abnormalities.

Chance of Having a Baby With Any Chromosomal Abnormality

Diagnosis is confirmed by evaluating a person's chromosomes. This is usually done as a blood test or during pregnancy by CVS or amniocentesis.

Only a minority of women have prenatal testing, so most boys with Klinefelter syndrome are not diagnosed with this condition before birth. In fact, many people with Klinefelter syndrome live their lives without knowing they have an extra X chromosome. Newborns look and act like any other healthy male child, so this condition is seldom recognized in the newborn period. Some individuals are identified with Klinefelter syndrome later in life when they are evaluated due to learning problems, delayed puberty, or infertility.  About 70% of men with Klinefelter Syndrome live their entire lives unaware of their diagnosis. Although these men may have experienced the usual features of the syndrome, the symptoms can be subtle enough that testing is not done.

Your chromosomes are in almost every cell of your body and it is impossible to correct the number of sex chromosomes present. Treatment is targeted toward the needs of each individual.

When learning disabilities are present, there are special services available. The services provided are the same as any other child who needs similar motor, reading, or language help. With early intervention (such as speech and physical therapy) and family support, most children with Klinefelter syndrome have performed just as well as their chromosomally normal peers.

Testosterone supplementation during puberty may be recommended by a pediatric endocrinologist in order to help develop secondary sexual characteristics.

For males with significant breast development, surgical treatment is possible.

Fertility issues would be managed through fertility specialists. With the aid of Assisted Reproductive Technologies (ART) and a male-factor infertility urologist, a minority of men with Klinefelter Syndrome are able to have biological children. Alternatives to biological children, such as adoption or sperm donation, are available.