Klinefelter syndrome is one of the most common chromosomal disorders, affecting 1/500 to 1/1,000 newborn males. Chromosomes, found in all body cells, contain genes. Genes provide specific instructions for body characteristics and functions. Each person typically has 23 pairs of chromosomes. One of these pairs (sex chromosomes) determines a person’s sex. A baby with two X chromosomes (XX) is female. A baby with one X chromosome and one Y chromosome (XY) is male.
Males with Klinefelter syndrome, may have two or more X chromosomes instead of one. The extra X chromosomes usually occur in all body cells. Sometimes the extra X chromosomes only occur in some cells (mosaic.)
The syndrome is not inherited from the parents. The addition occurs in the sperm, the egg, or after conception.
Signs and symptoms can vary. Many males are not diagnosed until puberty or adulthood. As many as two-thirds of men with the syndrome may never be diagnosed. Symptoms that may occur include: delayed, absent, or incomplete puberty, breast growth (gynecomastia), small testes and penis, less muscle development and hair growth, longer legs compared to torso, learning disabilities, fertility issues
Klinefelter syndrome can lead to weak bones (osteoporosis), varicose veins, and autoimmune diseases (when the immune system acts against the body), such as lupus or rheumatoid arthritis. XXY males have an increased risk for breast cancer and cancers that affect blood, bone marrow, or lymph nodes, such as leukemia. They also tend to have excess fat around the abdomen (which raises the risk of health problems), heart and blood vessel disease, and type 2 diabetes.
How is Klinefelter syndrome diagnosed?
Diagnosis is based on a physical examination, hormone testing, and chromosome analysis. The syndrome can also be diagnosed before birth, but testing is not routinely done at that time.
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