What causes it?

You and your partner are trying to get pregnant, but have been struggling, so you get tested by your doctor. They inform you that you have an extra X chromosome and this probably is the cause of your infertility. How does this happen? Can anything be done to correct it? If you do have children, can you pass the defect on to them?

Klinefelter SyndromeDefinition

All humans have 46 chromosomes, including two sex chromosomes that determine your gender. Females have two X sex chromosomes (XX) and males have an X and a Y (XY). In Klinefelter syndrome, a boy is born with an extra copy of the X chromosome (XXY). This occurs in all the cells. If only some cells receive the extra copy, this is called mosaic Klinefelter syndrome and usually has fewer symptoms. A rare form is having more than one extra copy of the X chromosome. This type results in severe symptoms. All of these are caused by a random error in genetic sequencing, not an inherited condition.

Klinefelter syndrome results in impaired testicular growth leading to a lower production of testosterone, which affects many things in the body, including fertility. Symptoms vary amongst individuals and can be mild, so the disorder often isn’t diagnosed until adulthood. For babies, symptoms can include weak muscles, slow motor development, speaking delays, and problems at birth (ex. undescended testicle). For boys, symptoms are taller than average stature, small/firm testicles, small penis, enlarged breast tissue (gynecomastia), weak bones, low energy levels, tendency to be shy/sensitive, difficulty expressing thoughts/feelings, problems, reading/writing/spelling/doing math, longer legs with a shorter torso and broader hips compared to other boys, and absent/delayed/incomplete puberty. For teens, they can have less muscle and body/facial hair than other male teens. For men, symptoms are low/no sperm count, small testicles/penis, low sex drive, taller than average height, weak bones, decreased facial/body hair, less muscular compared to other men, and enlarged breast tissue. Klinefelter syndrome can cause many different complications, like anxiety, depression, low self-esteem, emotional immaturity, impulsiveness, weak bones, heart/blood vessel disease, lung disease, breast cancer, other cancers, infertility, problems with sexual function, metabolic syndrome, autoimmune disorders, dental problems, and autism spectrum disorder.

TreatmentFast Facts - Klinefelter Syndrome

Treatment of Klinefelter syndromes is based on the symptoms. If caught early enough, testosterone replacement therapy can be started at the onset of puberty, which can stimulate the changes that normally occur. Unfortunately, this won’t improve fertility. For boys with cognitive delays, speech therapy, physical therapy, and educational support should be considered. There are different medications or surgical options for men with enlarged breasts to reduce/remove the excess tissue. For men with low sperm production trying to have children, a procedure, intracytoplasmic sperm injection (ICSI), may help. This involves removing the sperm from the testicle with a biopsy needle and injecting it into the egg.

There is a significant amount of emotional aspects to deal with when you have Klinefelter syndrome and there are several options for helping with this. The most important is to get psychological counseling. It’s also a good idea to learn as much as possible about the condition. For boys, it’s key to monitor their development and seek help from their doctor or school if you notice anything abnormal. In addition, be sure to keep all follow-up appointments. Encourage your son to participate in sports, physical activities, social opportunities, and group events. For men, it’s vital to continue the relationship with your doctor to prevent any complications. When it comes to family planning, talk to your doctor about what your options are. It can likewise help to connect with others who have the condition since they’ll understand what you’re going through.


There isn’t anything that can be done to prevent Klinefelter syndrome from occurring. The key to preventing long-term impacts is to recognize the symptoms early, so treatment isn’t delayed. The earlier treatment is started, the fewer effects the condition will have. If you notice anything abnormal with your child’s development, be sure to take them to the doctor as soon as possible.

Being diagnosed with Klinefelter syndrome can come as a shock. Thankfully, there are ways to manage. If you have any questions or concerns about Klinefelter syndrome, please speak with your doctor. If you would like more information, please visit the National Institute of Health’s National Human Genome Research Institute’s Klinefelter Syndrome page at https://www.genome.gov/Genetic-Disorders/Klinefelter-Syndrome