47/XXY  is estimated to occur in one out of 500 males, making it the  most common chromosomal disorder.  Rather than the normal male chromosome pattern, 46XY,  there is an extra X chromosome.  The result is the   47/XXY  arrangement. This variation happens when paired chromosomes fail to separate in the first or  second stage of meiosis.

For many years, this condition has been called Klinefelter Syndrome, named for Dr. Harry Klinefelter, who published a report about nine men with enlarged breasts, sparse facial and body hair, small testes, and an inability to produce sperm.  However, because the manifestation of 47XXY varies from person to person, this complete syndrome is not found in the majority of XXY's.   Some men may have only a few of the characteristics described in that report.   Thus, medical researchers prefer the term XXY when describing this condition. 

Some variations  include 46XY/47XXY mosaicism; 48XXXY 48XXYY; and 46XX males, which is termed sex-reversal syndrome

The exact cause of XXY is unknown.  The extra chromosome can come from either parent.

Diagnosis can occur at any time in a person’s life and many XXY's go undiagnosed for years.  A procedure known as a genetic karyotype, where a small blood sample is drawn and checked for chromosomal abnormalities, will confirm diagnosis.

At present, diagnosis is likely to be made—

• prenatally

• at puberty when adolescent development is not proceeding in the typical way

• during a couple's fertility studies

• if continuing physical or psychological difficulties are present.
  

XXY's  have an increased risk for

• autoimmune disorders, including type II diabetes,

• autoimmune thyroiditis

• hypothyroidism

• breast cancer 

• osteoporosis

• leg ulcers 

• depression

Generally, XXY males are infertile, but a semen analysis is suggested to confirm this issue.  Some 46XY/47XXY's have preserved testicular function.

Recent advances in fertility treatments, such as ICSI, (intracytoplasmic sperm injection) have enabled XXY males to reproduce children without any chromosomal abnormalities.  Other couples turn to adoption or donor insemination to create families. 

While XXY individuals  can find excellent medical care through family physicians and internists, an endocrinologist, familiar with this condition, can provide a more specialized approach to  care in terms of monitoring testosterone therapy  and in the  treatment of related conditions.  

No one can predict for certain what effect the extra chromosome will have on an individual. Personalities are as varied in this group as in the general population. The spectrum of manifestations is wide.  However, the following characteristics are said to occur more often in children with XXY.  Keep in mind that a child may have only one symptom, while another may have more:

• delayed speech

• gross and fine motor delays

• sensory integration difficulties, including sensitivity to noise

• hypotonia or low muscle tone

• attention deficits

• auditory processing problems

• language-based learning disabilities, including reading difficulties

• social Skill deficits

• anxiety

• self-esteem issues

• depression

• gynecomastia or swelling of breast tissue during puberty