A mild degree of breast development
(gynaecomastia) occurs in about two thirds
of boys with KS. Usually it resolves without
any treatment, but very rarely it can persist
and cause embarrassment. In such cases,
the excess breast tissue can be removed.
be used to explain the need for hospital
visits and other tests.
Fertility
Feedback
Men with KS do not usually produce
sperm, so they have always been
considered to be infertile, except in very
rare cases. Many males with KS are only
diagnosed when they are found to be
infertile, having been unaware of any
problems. The lack of sperm does not
affect the ability to have sexual
intercourse, and the sex life of men with
KS is usually normal. Many men are able
to have children with the help of donor
insemination, which can be arranged
through a fertility clinic or assisted
conception unit.
Recently, new techniques of sperm
retrieval and fertilisation have succeeded
in finding living sperm in a few men with
KS, and they have been able to become
fathers.
When should a boy with
Klinefelter syndrome be told
about his condition?
It is best to begin to explain things in
simple terms that the boy can understand
from the age of about 10 or 11 years.
Statements like "the blood test showed a
change in the cells that could mean you
grow too tall and put on weight easily" can
Further information
Human Fertilisation and Embryology
Authority: www.hfea.gov.uk
We appreciate and encourage feedback. If
you need advice or are concerned about
any aspect of your care or treatment please
speak to a member of staff or contact the
Patient Advice and Liaison Service (PALS):
Klinefelter syndrome
(XXY)
Clinical Genetics
Freephone: 0800 183 0204
From a mobile or abroad:
0115 924 9924 ext. 65412 or 62301
E-mail: [email protected]
Letter: NUH NHS Trust, c/o PALS,
Freepost NEA 14614,
Nottingham NG7 1BR
www.nuh.nhs.uk
If you require a full list of references for this
leaflet please email
[email protected] or phone
0115 924 9924 ext. 67184.
The Trust endeavours to ensure that the
information given here is accurate and
impartial.
Adapted from leaflet by Clinical Genetics at Guy’s and St
Thomas’ NHS Foundation Trust.
Nicola Drury, Clinical Genetics © April 2015. All rights reserved.
Nottingham University Hospitals NHS Trust. Review April 2017.
Ref: 1045/v2/0415/AM.
This document can be provided in
different languages and formats. For
more information please contact:
Clinical Genetics Service
City Hospital
The Gables, Gate 3
Hucknall Road
Nottingham NG5 1PB
Tel: 0115 962 7728
Minicom: 0115 962 7749
50
Public information
Introduction
What causes Klinefelter syndrome?
People are usually born with 46
chromosomes, which are arranged in 23
pairs. One of each pair of chromosomes
comes from our mother in the egg and the
other of the pair comes from our father in
the sperm.
The condition occurs by chance and we do
not know what causes it. The extra X
chromosome is present due to a ‘genetic
mistake’ occurring at the time of cell division
to produce the egg or sperm that went to
make that baby. There is a slightly higher risk
of the condition occurring in the children of
older mothers.
The chromosomes are numbered from one
to 22 and the last pair, known as X and Y,
are called the sex chromosomes because
they determine gender. Males usually have
the sex chromosomes XY and females
usually have the sex chromosomes XX.
Occasionally a boy is born with an extra X
chromosome and this is known as
Klinefelter syndrome. The picture below
shows the chromosome pattern of someone
with Klinefelter syndrome.
How does it affect boys?
Young children
Baby boys with Klinefelter syndrome (KS) do
not appear different from other boys at birth
although they may be slightly smaller than
average. The genitals appear normal,
although often one or both testicles will not
have come down into the scrotum. This can
be corrected by a minor operation early in
life.
Children with KS may be slower to learn to
talk than other children. If this is a problem,
then speech therapy will be helpful.
About one in 1,000 boys has an extra X
chromosome, but often they are unaware of
it. There are an estimated 25,000 boys and
men with XXY in Britain. Even though these
boys have an extra X chromosome, they are
100 per cent male. However, they usually
have fertility problems as they get older.
The condition is named after Dr Harry
Klinefelter, who first described the condition
in 1942.
School children
Research has shown that the average
intelligence (known as IQ) of boys with KS is
lower than that of boys with the usual number
of chromosomes. For example, in one study,
the average IQ score was 98 in boys with KS
compared with 112 in other boys. The range
of IQ is between 70 to 130, so it is clearly
possible to have above average intelligence
with this condition.
Boys with KS tend to do less well at school
than their brothers and sisters, and may feel
discouraged by this. It is important to try not
to compare children within a family.
Approximately 75 per cent of boys with KS
have difficulty learning to read, and may
need additional support at school. This is
possibly related to difficulties such as short
attention span and poor memory. These
types of problem are not unique to boys
with KS. They can be helped with patience
and an appreciation that they may need
much more repetition to retain what they
have learned. Boys with KS may also
experience problems with the social side of
school as they are often quite sensitive and
may become tearful.
Growth
Boys with KS often grow faster than usual.
On average, a man with KS will be about
186 cm (6 ft 2 in) tall. If it appears that a
boy will be exceptionally tall, his growth can
be slowed down by a course of injections.
This would be advised by a growth
specialist or endocrinologist and is
considered before the boy’s height has
become a problem. Muscle development in
KS is sometimes poor, but this can be
improved with exercise.
About 75 per cent of affected boys put on
extra fat from about seven years of age,
particularly around the waistline, so it is
important to try to maintain a healthy diet to
prevent this.
Puberty
Puberty usually occurs at the normal time
and usually progresses normally. In some
cases the growth of the penis may slow
down towards the end of puberty and hair
growth may be quite sparse. This can be
treated with testosterone supplements
given towards the end of puberty.