Overview

Klinefelter syndrome (KS), also called Klinefelter's or XXY, is a genetic chromosomal condition in which males are born with an extra copy of the X chromosome, resulting in a total of 47 chromosomes instead of the usual 46. While males typically carry one X and one Y chromosome (46, XY), those with KS exhibit an additional X chromosome (47, XXY). The syndrome can lead to different physical traits, cognitive delays and infertility. 

KS arises from random errors during cell division after fertilisation resulting in an abnormal number of sex chromosomes. There are two primary genetic variations of KS. Approximately 90% of cases involve an extra X chromosome (47, XXY), while the remaining 10% have different variations, such as mosaicism with two cell types, additional extra sex chromosomes (48, XXXY; 49, XXXXY), or atypical X chromosomes. Nonetheless, Klinefelter syndrome (KS) is neither inherited nor can it be passed down through generations.

Diagnosis usually occurs in adulthood due to fertility issues, as most men with KS have a low sperm count or no sperm at all. KS affects around 1 in every 600 male births, with approximately 64% of cases going undiagnosed throughout life. However, the syndrome can be identified during prenatal stages, before puberty, adolescence, or adulthood. Treatment is based on how severe the symptoms are and when they appear and can include hormone therapy.¹ 

Disease characteristics 

The main symptoms include a deficiency in testosterone, small and firm testicles, and infertility. The size of the testicles is a distinguishing feature of KS, setting it apart from men with normal testicular function and raising suspicion about the condition. The extent of testosterone deficiency can differ significantly, leading to a clinical presentation that spans from nearly normal testosterone levels to pronounced hypogonadism. 

Although the majority of individuals experience puberty with minimal symptoms and attain a typical penis size, around 70% report a decline in libido and erectile function starting at approximately 25 years of age. 

Low testosterone can lead to mild anaemia and sparse facial and body hair growth. Other issues such as back pain and bone-related problems like osteopenia and osteoporosis may also arise. People with KS also present with gynecomastia alongside a tall physique, long legs and a short torso.

Individuals diagnosed with Klinefelter syndrome may experience verbal and cognitive impairments and a significant percentage, approximately 75%, may encounter learning challenges. Additionally, these individuals may exhibit attention deficits, and the development of social skills can be challenging. As a result, those with KS frequently attain lower levels of performance and professional achievement compared to their family members. 

For many affected individuals, diagnosis often occurs because of challenges with fatherhood. Azoospermia, the absence of sperm, is present in over 90% of cases, meanwhile fewer than 10% exhibit some degree of reduced motility and morphology in their sperm. Histological examinations of the testicles typically show hyalinising fibrosis. 

These are structural changes in the seminiferous tubules, which can result in either the complete absence of sperm production or limited production in certain areas of the testicles with the rare condition Leydig cell hyperplasia (LCH). Natural conception in individuals with KS is extremely uncommon.^2,3 

Symptoms

Some of the symptoms and psychosocial issues that are related to Klinefelter syndrome (KS):²

• Tall accompanied by long legs
• Testicular atrophy
• Underdevelopment in sexual characteristics, like loss of libido, erectile dysfunction, infertility, etc.
• Osteoporosis
• Attention issues
• Restricted verbal skills
• Learning obstacles
• Dyslexia
• Social adjustment issues
• Professional growth

Diagnosis

After suspecting Klinefelter syndrome based on a physical examination, healthcare providers often recommend taking a blood sample to assess reproductive hormone levels. The presence of an extra X chromosome is confirmed through a Karyotype test.

The laboratory tests used in KS involve assessing various parameters, including FSH, LH, sperm count, and other indicators. These are presented as follows:²

• Azoospermia
• Oligoasthenoteratozoospermia
• Testosterone
• Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)
• Barr bodies (Inactive X chromosomes)
• 47, XXY karyotype or mosaicism
• Red blood cell (RBC) count
• Bone density

FAQs

At what age is klinefelter syndrome diagnosed?

KS is not typically realised until adulthood, with the majority of diagnosed instances being identified at a later stage when certain clinical signs are noticed. For example infertility, verbal and cognitive difficulties, tall stature or genital deformity.

What is the life expectancy of someone with klinefelter syndrome?

Life expectancy is normal or slightly reduced depending on the person. If due to the disorder the person develops a secondary disease their life expectancy will be reduced.

Is there a cure for klinefelter syndrome?

There are no current cures for Klinefelter syndrome because it is a genetic disorder, however, the symptoms can be managed with the appropriate treatment.

Summary

Klinefelter syndrome (KS) is the most common chromosomal abnormality, occurring when a boy is born with an extra X chromosome, resulting in 47 chromosomes instead of the usual 46. It's a fairly common genetic condition that affects fertility due to testosterone deficiency. The main symptoms include small and firm testes, along with infertility. Though the diagnosis is simple due to small testicular volume, Klinefelter syndrome is often missed or left untreated. Children, adolescents and adults with KS may face verbal development, learning, and social skills issues.