What is Klinefelter syndrome?

What is Klinefelter syndrome?

A typical male has a total of 46 chromosomes (packages of DNA) – one copy of an X chromosome and one copy of the Y chromosome (46, XY). A typical girl has two copies of the X chromosome (46, XX). There are a number of different conditions where an individual may have more or less than the expected X or Y chromosomes. Klinefelter syndrome (KS) is a genetic condition where there’s an extra X chromosome present in a male’s genetic code. Instead of having a total of 46 chromosomes, they have 47 — with two copies of the X chromosome and one copy of the Y chromosome (47,XXY). There are some forms (called mosaic) where only some (not all) of the person’s cells have this change (other cells can either have the typical 46 XY, or can have another abnormality).

Klinefelter syndrome is a congenital condition, which means it’s present from the time of birth. There are certain tests that can be done during the mother’s pregnancy that can diagnose it before birth, however more often it’s diagnosed later in life. If not found before birth, it can sometimes be diagnosed because the baby has a smaller penis than expected, or later in the teenage years if puberty doesn’t start or progress as expected. Many males may not be diagnosed at all, or only when experiencing fertility challenges later in life (if they’re having a difficult time getting pregnant with their partner).

In most cases, the differences in their puberty and/or fertility are because the testicles have early “failure” and cannot make enough testosterone and/or sperm. This results in these individuals needing testosterone replacement and testing for fertility.

People with Klinefelter syndrome are also more likely to develop certain conditions that are part what is known as metabolic syndrome. These conditions include:

• Hypertension (high blood pressure).
• Type 2 diabetes.
• High cholesterol and fats called triglycerides in the blood.

Males with Klinefelter syndrome are also more likely to develop:

• Gynecomastia (breast growth in a male).
• Breast cancer.
• Tremors.
• Osteoporosis (weakened bones).
• Autoimmune diseases (including type 1 diabetes, thyroid disease, lupus and rheumatoid arthritis).
• Seizure disorders.
• Learning differences (especially language skills).

This condition can be managed by treating the symptoms — often including hormone replacement, physical therapy and behavioral therapy.