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Klinefelter Syndrome (XXY) |
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What is a chromosome disorder and what is its significance? |
Chromosomes are the structures in which our hereditary material ( DNA )
is packed. A healthy person has 46 chromosomes (23 pairs). One chromosome of each pair
(i.e. a total of 23 chromosomes) is donated by each parent to the fetus.
Twenty-two pairs are called autosomes, and the 23rd pair consists of the sex chromosomes (X and Y).
Females have two X chromosomes and males have one X and one Y. The chromosome pairs are arranged and
numbered by size and shape, and each has different genes. Because there are two copies of each chromosome,
there is effectively a duplicate gene system (one maternal and the other paternal), each identical in
sequence to the other.
A change in the number or structure of the chromosomes in pairs 1 - 22, causing an addition or
deletion of chromosomal information in these pairs compared with the normal state,
constitutes a significant medical problem.
In the great majority of cases, this change is expressed as severe structural or functional defects
in the tissues and/or mental retardation.
For example, an extra number 21 chromosome, resulting in three instead of the normal two so that there are 47
chromosomes altogether, causes Down syndrome.
An extra number 18 chromosome, which is larger and therefore contains more genes, manifests as a more
severe disorder called trisomy 18.
In this syndrome, there are severe defects, and it usually ends in death soon after birth or even in the uterus.
This is also the case with a deletion of the whole or a part, however small, of chromosome 18.
Conversely, the clinical manifestation of a change in the number of sex chromosomes (X or Y) or
their structure, as is the case in Klinefelter syndrome, is usually less severe.
See under "Chromosomes".
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What is Klinefelter syndrome (XXY)? |
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This syndrome is caused by an extra X chromosome in males, so that
these boys have two X chromosomes and one Y chromosome, giving a total of 47 chromosomes
altogether.
The frequency is estimated to be 1:600 live male births.
This syndrome is one of the common causes of small testes in males.
The main characteristics are a relatively short stature, very small testes, usually only
discovered in adolescence, infertility in 100% of cases, and an increased likelihood of
learning disorders and behavioral problems.
Some of these males need hormonal therapy in adolescence so that they will not develop
a female figure and breasts (gynecomastia).
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There is a wide spectrum of developmental variation. Some affected children have
normal intelligence, but there is a slightly increased risk of a reduced level of
intelligence, speech disorders and reading problems.
They are not usually mentally retarded, but some patients need support with their
studies. In addition, problems with social adjustment have been reported in some
of these children, such as shyness, etc.
Today, with the development of
in vitro fertilization and ICSI techniques, there is a technical possibility
that some men with this karyotype might be able to father children, despite their
significant infertility problem.
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Klinefelter's Syndrome
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