Alternative names for Klinefelter’s syndrome
Klinefelters syndrome; Klinefelter syndrome; 47 XXY syndrome; XXY syndrome; XXY trisomy.
What is Klinefelter’s syndrome?
Klinefelter’s syndrome is a genetic disorder whereby a boy is born with one or more extra X chromosomes. Chromosomes carry our genetic information. Humans have 23 pairs of chromosomes (total 46 chromosomes), which are inherited from both parents. One pair is the sex chromosomes, which determine gender - boys usually have an X and a Y chromosome (XY), whereas girls have two X chromosomes (XX).
The extra one or more X chromosomes in Klinefelter’s syndrome cause a number of features including tall stature, reduced fertility, development of breast tissue and problems with language and social interactions. There is, however, substantial variation in clinical presentation among individuals and many cases remain undiagnosed.
Klinefelter’s syndrome is named after Dr Henry Klinefelter, who first described a collection of symptoms present in men with an extra X chromosome; therefore, it is sometimes called 47 XXY (47 refers to the total number of chromosomes in this condition).
What causes Klinefelter’s syndrome?
Klinefelter’s syndrome is caused by men having an extra one or more X chromosomes. This occurs as a result of a problem in the way cells divide either before or after conception. The usual 47 XXY pattern of Klinefelter’s syndrome accounts for around 80% of cases, however, there are also other variations. Sometimes, more than one extra X chromosome is present resulting in 48 or 49 chromosomes (48 XXXY or 49 XXXXY). Another variation is that not all cells in the affected individual have an extra X chromosome; this is known as mosaicism. The greater the number of cells containing an extra X chromosome, the more likely it is to lead to features of Klinefelter’s syndrome.
What are the signs and symptoms of Klinefelter’s syndrome?
Not all individuals with this condition have the same symptoms or to the same degree; because of this variability, cases often remain undiagnosed. Symptoms depend on the proportion of cells in the body that contain an extra X chromosome (XXY), how much testosterone is being produced and the age at diagnosis.
From early school age, boys with Klinefelter’s syndrome tend to be taller (increased leg length) and may have reduced coordination compared with other boys. This increase in height is maintained throughout life.
From the time of puberty, most affected boys fail to make as much testosterone as unaffected boys. This can lead to a taller, less muscular appearance with less facial and body hair; impaired sex drive (libido) and difficulties maintaining erections (potency); and lower energy levels. Men with Klinefelter’s syndrome may develop breast enlargement (gynaecomastia) and thinning of the bones (osteoporosis). Characteristically, they have small, firm testes with a low or absent sperm count; almost all men who are 47 XXY will be infertile. However, most men with Klinefelter’s syndrome may have a normal sex life.
A significant proportion of men with Klinefelter’s syndrome have some kind of difficulties with language (problems reading or learning to talk initially) or executive functions (problem solving, task switching, planning etc) not dissimilar to people with dyslexia. They may also have trouble with social interactions throughout life, but particularly in childhood. The majority of men with Klinefelter’s syndrome lead an independent life, forming relationships and getting a normal job and have a normal life span.
How common is Klinefelter’s syndrome?
Klinefelter’s syndrome only affects men. It is one of the most common chromosome abnormalities in men. About one of every 650 live male births has an extra X chromosome, but many do not have any symptoms. Importantly, up to 3% of infertile men have Klinefelter’s syndrome.
Is Klinefelter’s syndrome inherited?
Klinefelter’s syndrome is a genetic condition but it is not inherited from the parents. In the vast majority of boys, there are no other affected family members; it occurs sporad