Klinefelter syndrome47 X-X-Y syndrome; XXY syndrome; XXY trisomy; 47,XXY/46,XY; Mosaic syndrome; Poly-X Klinefelter syndrome
Klinefelter syndrome is a genetic condition that occurs in males when they have an extra X chromosome.
Most people have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. The 2 sex chromosomes (X and Y) determine if you become a boy or a girl. Girls normally have 2 X chromosomes. Boys normally have 1 X and 1 Y chromosome.
Klinefelter syndrome results when a boy is born with at least 1 extra X chromosome. This is written as XXY.
Klinefelter syndrome occurs in about 1 out of 500 to 1,000 baby boys. Women who get pregnant after age 35 are slightly more likely to have a boy with this syndrome than younger women.
Infertility is the most common symptom of Klinefelter syndrome.
Infertility means you cannot get pregnant (conceive). There are 2 types of infertility:Primary infertility refers to couples who have not become preg...Read Article Now Book Mark Article
Symptoms may include any of the following:
- Abnormal body proportions (long legs, short trunk, shoulder equal to hip size)
- Abnormally large breasts (gynecomastia)
When abnormal breast tissue develops in males, it is called gynecomastia. It is important to find out if the excess growth is breast tissue and not ...Read Article Now Book Mark Article
- Sexual problems
- Less than normal amount of pubic, armpit, and facial hair
- Small, firm testicles
The testes are 2 egg-shaped male reproductive organs located in the scrotum. They produce sperm and the male hormone, testosterone.Read Article Now Book Mark Article
- Tall height
- Small penis size
Exams and Tests
Klinefelter syndrome may first be diagnosed when a man comes to the health care provider because of infertility. The following tests may be performed:
- Karyotyping (checks the chromosomes)
Karyotyping is a test to examine chromosomes in a sample of cells. This test can help identify genetic problems as the cause of a disorder or diseas...Read Article Now Book Mark Article
- Semen count
Semen analysis measures the amount and quality of a man's semen and sperm. Semen is the thick, white fluid released during ejaculation that contains...Read Article Now Book Mark Article
Blood tests will be done to check hormone levels, including:
- Estradiol, a type of estrogen
Estradiol, a type of estrogen
An estradiol test measures the amount of a hormone called estradiol in the blood. Estradiol is one of the main types of estrogens.Read Article Now Book Mark Article
- Follicle stimulating hormone
Follicle stimulating hormone
The follicle stimulating hormone (FSH) blood test measures the level of FSH in blood. FSH is a hormone released by the pituitary gland, located on t...Read Article Now Book Mark Article
- Luteinizing hormone
The LH blood test measures the amount of luteinizing hormone (LH) in blood. LH is a hormone released by the pituitary gland, located on the undersid...Read Article Now Book Mark Article
A testosterone test measures the amount of the male hormone, testosterone, in the blood. Both men and women produce this hormone. The test described...Read Article Now Book Mark Article
Testosterone therapy may be prescribed. This can help:
- Grow body hair
- Improve appearance of muscles
- Improve concentration
- Improve mood and self esteem
- Increase energy and sex drive
- Increase strength
Most men with this syndrome are not able to get a woman pregnant. An infertility specialist may be able to help. Seeing a doctor called an endocrinologist may also be helpful.
These sources can provide more information on Klinefelter syndrome:
- Association for X and Y Chromosome Variations -- genetic.org
- US National Library of Medicine, MedlinePlus -- medlineplus.gov/klinefeltersyndrome.html
Enlarged teeth with a thinning surface is very common in Klinefelter syndrome. This is called taurodontism. This can be seen on dental x-rays.
Klinefelter syndrome also increases the risk of:
- Attention deficient hyperactivity disorder (ADHD)
Attention deficient hyperactivity disor...
Attention deficit hyperactivity disorder (ADHD) is a problem caused by the presence of one or more of these findings:Not being able to focusBeing ove...Read Article Now Book Mark Article
- Autoimmune disorders, such as lupus, rheumatoid arthritis, and Sjögren syndrome
Systemic lupus erythematosus (SLE) is an autoimmune disease. In this disease, the immune system of the body mistakenly attacks healthy tissue. It c...Read Article Now Book Mark Article
Rheumatoid arthritis (RA) is a disease that leads to inflammation of the joints and surrounding tissues. It is a long-term disease. It can also aff...Read Article Now Book Mark Article
Sjögren syndrome is an autoimmune disorder in which the glands that produce tears and saliva are destroyed. This causes dry mouth and dry eyes. The...Read Article Now Book Mark Article
- Breast cancer in men
Breast cancer is cancer that starts in the tissues of the breast. There are two main types of breast cancer:Ductal carcinoma starts in the tubes (du...Read Article Now Book Mark Article
- Learning disabilities, including dyslexia, which affects reading
- A rare type of tumor called an extragonadal germ cell tumor
- Lung disease
Lung disease is any problem in the lungs that prevents the lungs from working properly. There are three main types of lung disease:Airway diseases -...Read Article Now Book Mark Article
Osteoporosis is a disease in which bones become fragile and more likely to break (fracture).Read Article Now Book Mark Article
- Varicose veins
Varicose veins are swollen, twisted, and enlarged veins that you can see under the skin. They are often red or blue in color. They most often appea...Read Article Now Book Mark Article
When to Contact a Medical Professional
Contact your provider if your son does not develop secondary sexual characteristics at puberty. This includes facial hair growth and a deepening of the voice.
A genetics counselor can provide information about this condition and direct you to support groups in your area.
Allan CA, McLachlan RI. Androgen deficiency disorders. In: Jameson JL, De Groot LJ, de Kretser DM, et al, eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 139.
Jones KL, Jones MC, Campo MD. Recognizable patterns of malformation. In: Jones KL, Jones MC, Campo MD, eds. Smith's Recognizable Patterns of Human Malformation. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 1.
Matsumoto AM, Anawalt BD, Testicular disorders. In: Melmed S, Auchus RJ, Goldfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 19.
Nussbaum RL, McInnes RR, Willard HF. The chromosomal and genomic basis of disease: disorders of the autosomes and sex chromosomes. In: Nussbaum RL, McInnes RR, Willard HF, eds. Thompson & Thompson Genetics in Medicine. 8th ed. Philadelphia, PA: Elsevier; 2016:chap 6.
Karyotyping - illustration
Karyotyping is a test used to identify chromosome abnormalities as the cause of malformation or disease. The test can be performed on a sample of blood, bone marrow, amniotic fluid, or placental tissue.
Review Date: 10/13/2022
Reviewed By: Anna C. Edens Hurst, MD, MS, Associate Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.