Also known as 47,XXY
What is Klinefelter syndrome / XXY?
Klinefelter syndrome, also known as 47,XXY or XXY, is a sex chromosome aneuploidy characterized by the presence of an additional X chromosome in males. Men and boys with XXY often have tall stature, testicular dysfunction resulting in testosterone deficiency and infertility, low muscle tone, risk for gynecomastia, and risks for neurodevelopmental disorders including developmental delays (especially regarding expressive language), learning disabilities, ADHD, anxiety, and social difficulties. The presence and severity of these symptoms are highly variable between individuals, with some boys having few symptoms while others are more significantly affected.
Who gets XXY?
Approximately 1 in 650-820 males are born with XXY, up to however many males are not diagnosed until adulthood when evaluated for infertility or may go their entire lives without being diagnosed. The onset of prenatal cell-free DNA screening has increased the identification of XXY in newborns and active research is being done to redefine the natural history of this condition when identified at birth.
What causes XXY?
XXY is caused by an extra X chromosome in boys, commonly due to the presence of an extra X chromosome in the egg or sperm at the time of conception due to nondisjunction (when chromosomes do not divide properly) and is not typically inherited.
How is XXY diagnosed?
XXY is a chromosome condition which can be diagnosed from blood tests. Tests that can diagnose XXY include a karyotype (chromosome analysis looking at the number and structure of chromosomes in cells), a chromosomal microarray (a more detailed chromosome study looking for deletions or duplications across all chromosomes) or genetic sequencing (reading through the DNA sequence carried on the chromosomes). XXY may be suspected based on physical or neurodevelopmental differences during childhood and can be identified before birth by prenatal screening and/or diagnostic testing, such as amniocentesis.
What is the treatment for XXY?
Treatments for XXY are specific to managing symptoms and may include testosterone treatment beginning in adolescence to complete puberty and support bone health, infertility treatment by microTESE and ICSI, as well as psychological and/or academic supports, when indicated.
Frequently Asked Questions
Why did I get Klinefelter syndrome / XXY?
Klinefelter syndrome/XXY is not caused by anything a person does or doesn't do, as it results from a biological process in which the chromosomes mis-divide, called nondisjunction.
Will my XXY get worse?
The symptoms associated with XXY may or may not change overtime. Some symptoms, such as developmental delays or learning disabilities may be present from a very young age, whereas other symptoms, such as tall stature, may become more apparent later in childhood.
What things can I discuss with my primary care physician about XXY?
There have been many articles published in medical literature to help guide physicians on how to best care for people with this condition. Talk with your doctor about your concerns or your child's struggles to ensure that appropriate referrals and evaluations are being pursued. Even though infertility is associated with this condition, some men have been able to father biologic children using fertility interventions. Referrals for further fertility evaluation may also be helpful.