Klinefelter Syndrome: When Boys Have An Extra X-chromosome

Klinefelter syndrome (often referred to as Klinefelter's, KS or XXY) is a sex chromosome disorder in which boys are born with an extra X chromosome.

Chromosomes are bundles of genes present in each cell of the body. There are two types of chromosomes, known as the sex chromosomes, that specify the genetic sex of a baby. These are designated as either X or Y.

Typically, a female baby has 2-X chromosomes (XX), and a male has 1-X and 1 Y (XY). However, in Klinefelter syndrome, a boy is born with an additional X chromosome.

The X chromosome is NOT a "female" chromosome, and is found in both girls and boys. Although, the presence of a Y chromosome indicates male sex.

Boys and men having Klinefelter syndrome are still genetically male, and sometimes will not recognize having this extra chromosome, but sporadically it may cause issues that may demand treatment.


Frequency Of Klinefelter's Syndrome

Klinefelter syndrome impacts nearly 1 in 660 newborn boys worldwide. It is one of the most widespread sex chromosome disorders, which are conditions caused by alterations in the number of sex chromosomes.


What Causes Klinefelter's Syndrome?

Boys having Klinefelter syndrome are born with it. It's also known as XXY because they have an additional X chromosome in all or most of their cells.

Generally, an individual has 46 chromosomes in each cell, classified into 23 pairs, which incorporates two sex chromosomes. One-half of the chromosomes are inherited from the mother and the second half from the father. The chromosomes incorporate genes, which decide an individual's attributes, such as height, eye colour etc. Boys generally have one X chromosome and one Y chromosome, but boys with Klinefelter's (XXY) syndrome have an additional X chromosome.

Klinefelter syndrome has nothing to do with what parents did or didn't do. The syndrome is caused by a random error in cell division that occurs when a parent's reproductive cells are being developed.

If one of these defective cells leads to a prosperous pregnancy, the baby will have the XXY condition in either of all some of his cells. Some boys can even have more than two X chromosomes (XXXY or XXXXY, for example), which elevates the risk of acute symptoms and other health problems.

When a boy takes birth with the XXY syndrome in only some of his cells, it's known as mosaic Klinefelter's syndrome. At times, boys and men with this condition can have less severe signs and symptoms than others with the same disorder.


What Are The Symptoms Of Klinefelter's Syndrome?

The symptoms of Klinefelter syndrome differ widely among males with the disease. Many boys experience little or no signs. The condition may go undetected until manhood, or it may never be detected at all. For others, the condition has a considerable effect on appearance and growth.

People of different age groups may experience various symptoms.


  • Problems at birth, like testicles that haven't come down into the scrotum
  • Slow motor development - taking longer than usual to sit, crawl and walk
  • Muscle weakness
  • Delay in speaking

Boys and teenagers

  • Low energy levels
  • Weak bones
  • Taller than usual height
  • Longer legs, broader hips, and shorter torso as compared to other boys
  • Absent, delayed or inadequate puberty
  • After puberty, less muscle and less facial and body hair as compared to other teens
  • Enlarged breast tissue (gynecomastia)
  • Small penis
  • Small, firm testicles
  • A tendency to be shy and sensitive
  • Trouble expressing feelings and thoughts or socializing
  • Difficulty with reading, writing, spelling or math


  • Small testicles and penis
  • Low sperm count or no sperm
  • Low sex drive
  • Weak bones
  • Less muscular compared with other men
  • Increased belly fat
  • Enlarged breast tissue
  • Taller than usual height
  • Decreased facial and body hair

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What Health Issues Can Happen In Klinefelter Syndrome?

Many boys and men with Klinefelter syndrome will not be considerably affected and can live typical, healthy lives.

Infertility tends to be the significant problem; however, there are various treatment alternatives that can help.

But men with Klinefelter syndrome are at somewhat higher risk of developing other medical conditions, such as:

  • weak and fragile bones (osteoporosis)
  • an underactive thyroid gland (hypothyroidism)
  • cardiovascular disease and blood clots
  • anxiety, learning difficulties and depression – however intelligence is often unaffected
  • male breast cancer – although it is very rare
  • type 2 diabetes
  • autoimmune disorders (where our defensive system attacks its own body tissue by mistake), for example, lupus

These health problems can generally be treated if they do take place, and testosterone replacement therapy may help minimize the risk for some of them.


How Is Klinefelter’s Syndrome Diagnosed?

Since Klinefelter syndrome is not easily noticeable, several parents don't realize their son has it until he reaches his adolescence years or exhibits delays in puberty. In some cases, parents who are concerned about their son's development check with a doctor, and the diagnosis suggests Klinefelter syndrome. This can be of great help because the sooner a boy is identified with Klinefelter syndrome, the more effective the treatments generally are.

For the diagnosis of Klinefelter syndrome, doctors often start by enquiring about any learning or behaviour problems and reviewing the boy's testicles and body measurements.

The two primary tests used to confirm the diagnosis of Klinefelter syndrome are:

  • Hormone testing - The doctor takes a small blood sample to test for unusual hormone levels.
  • A chromosome analysis, or karyotype - The doctor takes a small blood sample for this test as well. He then monitors the number of chromosomes to discern whether the XXY syndrome is present.


How Is Klinefelter's Syndrome Treated?

There's no cure for Klinefelter syndrome, although some of the problems concerned with the condition can be treated if required.

Possible treatment alternatives include the following:

  • testosterone replacement therapy
  • speech and language therapy during childhood to assist with speech development
  • psychological support for certain mental health disorders
  • fertility treatment - alternatives include artificial insemination utilizing donor sperm or possibly intracytoplasmic sperm injection (ICSI), where the sperm is taken out during a small operation is utilized to fertilize an egg in a laboratory
  • educational and behavioural support at school to support any learning or behaviour problems
  • occupational therapy to help improve any coordination challenges related to Dyspraxia
  • breast reduction surgery to take off excess breast tissue
  • physiotherapy to help develop muscle and increase strength






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