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2. medicine
3. genetics

Triple X
What is Triple X?
Triple X is a genetic condition that is caused by an extra chromosome. To understand
what Triple X is, it is helpful to know something about genes and chromosomes.
.
What are genes and chromosomes?
Our bodies are made up of millions of cells. These cells are grouped together to make up
parts of the body such as our muscles, our heart and our brain. Cells carry all the
information needed for our bodies to work. The information is contained in our genes. We
each inherit two copies of most genes, one copy from our mother and one copy from our
father. Genes act like a set of instructions, controlling our growth and how our bodies work.
Genes are responsible for many of our characteristics, such as our eye colour, blood type
or height.
Genes are carried on thread-like structures called chromosomes. It is possible to see
chromosomes under a microscope. Picture 1 shows what they look like.
Picture 1. Chromosomes
as they appear under a
microscope
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Usually, each of us has 46 chromosomes in every cell. We inherit our chromosomes from
our parents, one set of 23 chromosomes from our mother and one set of 23 chromosomes
from our father. So we have two sets of 23 chromosomes, or 23 pairs. The pairs of
chromosomes are numbered according to size, starting with the largest chromosome,
chromosome 1, through to chromosome 22. The remaining pair are called the sex
chromosomes.
Picture 2. The chromosomes arranged according to size; chromosome 1
is the largest. The two chromosomes at lower right are the sex
chromosomes.
There are two kinds of sex chromosome, one called the X chromosome and one called the
Y chromosome, and they control whether a person is male or female. Females normally
have two X chromosomes (XX). A female inherits one X chromosome from her mother and
one X chromosome from her father. Males normally have an X chromosome and a Y
chromosome (XY). A male inherits an X chromosome from his mother and a Y
chromosome from his father.
Triple X
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Triple X affects only girls and is caused by an extra X chromosome. A girl or woman with
Triple X has three X chromosomes (47,XXX) rather than just two X chromosomes as
normal (46,XX).
It may happen that a girl or woman with Triple X is a mosaic. She has the normal number
of X chromosomes (XX) in some cells, and other cells contain an extra X chromosome
(XXX). The extent to which a mosaic is affected by the condition will depend upon the
proportion of XX cells to triple X cells (XXX cells) throughout her body.
What causes Triple X?
The majority of parents with a daughter with Triple X have a normal number of
chromosomes themselves. The extra X chromosome occurs either during the making of
the parents’ eggs and sperm, or shortly after an egg and sperm come together to make a
baby, at conception. It happens by chance and is not caused by anything that the parents
did or did not do.
Will it happen again?
It is very unlikely that Triple X will affect another child of the same couple. Some parents
decide to have a test in a future pregnancy to check the chromosomes of the baby.
Testing can be discussed at a genetics clinic.
How does an extra X chromosome affect a person?
The effect of having an extra X chromosome varies, but the majority of girls and women
with Triple X lead normal lives. They go to ordinary schools, have successful careers,
marry, have children, and live until old age. However, a few may experience problems
such as learning difficulties or behavioural problems.
Comparisons of girls with Triple X against girls with the usual two X chromosomes have
led to a general description of the effects of Triple X, as follows:
 First year of life
At birth, most girls with Triple X are normally developed, although some babies may be
floppy (hypotonic). This means that their muscle tone is lower than usual, so that an
affected baby may be a little slow to hold her head steady and to sit without support.
She may also be slightly small at birth in terms of weight, length and the size of her
head.
 Age 1 to 5 years
Most children can walk on their own and start to say single words at around the age of
1 year. Girls with Triple X usually do these things a little later, but they generally walk
and start to talk by 18 months of age. If an affected girl has no speech at all by 2 years
of age, she should be seen by the family doctor or health visitor, to check her hearing
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and general development. Speech therapy can help if speech is definitely delayed or
very unclear. Speech therapy can start when the child is between 3 and 4 years old,
but the problem with speech usually disappears after a few years. Girls with Triple X
can take longer over toilet training, but most girls will achieve this by 3½ to 4 years of
age. Girls with Triple X may be a little slower in learning to play with other children of
the same age.
 Girls at school (5 to 16 years of age)
Most girls with Triple X will experience some difficulty learning to read and write. Early
recognition of this helps to prevent the child from becoming overwhelmed or
disheartened. Extra teaching on a one to one basis can gradually overcome the
problem, and may also help with subjects such as mathematics. Girls with Triple X may
have difficulty remembering what they have learned recently, and they may need
information to be repeated more times in order to be able to fix it in their memory. A
teacher or parent needs patience with this genuine difficulty. For some girls with Triple
X, making friends at school can be a problem. This may result from lack of selfconfidence, if they find that they fail at things in which others of the same age appear to
succeed effortlessly. Parents can help build their daughter’s self-confidence by
accepting her worth as a person rather than expecting high achievements.
 Intelligence
The majority of girls with Triple X are within the normal range of intelligence. However,
the average intelligence of girls with Triple X is slightly lower than that of girls with the
usual number of chromosomes. It is possible to have Triple X and have above average
intelligence.
 Growth in girls with Triple X
Some girls with Triple X tend to grow rapidly between the ages of 4 and 9 years, so
they are taller than average. Rarely, growth may be excessive, requiring medical
advice and management. Puberty usually starts at the normal time and progresses
normally. Girls start to develop breasts at around age 11 years and start their periods
between 13 and 15 years of age.
 Parenthood
The majority of women with Triple X have no problem in becoming pregnant and they
go on to have healthy children. However, there is a small risk that these children will
have chromosome problems like their mothers. Women with Triple X who wish to have
children and who have any concerns about this should consult a genetic counsellor
before starting a family.
Girls and women with Triple X have no increased risk of any diseases during childhood or
in adult life. Some women have been reported to start menopause earlier than normal.
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Where can I get more information about Triple X?
This is only a brief guide to Triple X. More information can be obtained from your local
regional genetics centre or from these addresses:
Triple-X Family Network Support Group
32 Francemary Road
London
SE4 1JS
Tel: 020 8690 9445
e-mail: [email protected]
The Genetic Interest Group
Unit 4D,
Leroy House,
436 Essex Rd.,
London,
N1 3QP
Telephone: 020 7704 3141
e-mail: [email protected]
Web: www.gig.org.uk
Contact a Family
209-211 City Rd.,
London
EC1V 1JN
Tel: 020 7608 8700 Fax: 020 7608 8701
Helpline 0808 808 3555 or Textphone 0808 808 3556
(Freephone for parents and families, 10am-4pm, Mon-Fri)
e-mail: [email protected]
Web: www.cafamily.org.uk
This edition prepared July 2005
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Glossary (difficult words and their meanings): Triple X
This glossary is intended only to explain terms used in the information: Triple X. Words
shown in bold are defined elsewhere in the glossary.
(46,XX). Scientific abbreviation for the chromosomes usually found in women and
girls. There are 46 chromosomes, including two X chromosomes.
22, 24
(47,XXX). Scientific abbreviation for the chromosomes usually found in someone with
Triple X. There are 47 chromosomes, instead of the usual 46, including three X
chromosomes, instead of the usual two in a female.
cell . The human body is made up of millions of cells, which are like building blocks. There
are many specialised types of cells. These include skin cells, brain cells, and blood cells.
Cells in different parts of the body look different and do different things. Every cell (except
for eggs in women and sperm in men) contains all the body’s genes.
chromosomes. Thread-like structures which can be seen under the microscope and
contain the genes. Usually people have 46 chromosomes in every cell. There are two sex
chromosomes and 22 other pairs of chromosomes. Twenty-three chromosomes come
from the mother, and twenty-three come from the father. One chromosome of each pair
comes from each parent. (As an analogy: a chromosome is like a book; a gene is like a
story in the book).
conception. When an egg and a sperm join together to make the first cell of a new
baby.
egg. The mother’s contribution to the cell which will grow to make a new baby. The egg
contains 23 chromosomes; one from each pair in the mother. A sperm also contains 23
chromosomes one from each of the father’s pairs. The egg joins with a sperm to make a
complete cell. A baby develops from this first cell.
gene. Information needed for the body to work, stored in a chemical form on
chromosomes. Changes in genes alter the information and this can change how the body
works. Most genes are in pairs, one from the mother and one from the father. The two
genes of a pair are at matching places on a pair of chromosomes. Genes on the X
chromosome and the Y chromosome of males are not paired with each other; they do
not match. (As an analogy: a gene is like a story in a book, changes in genes are like
changes in a story).
genetic. Caused by genes, concerning genes.
genetic counsellor. A specialist who gives information and support to people who
have a history of a genetic condition in their family, or who are concerned about their risk
for inheriting or passing on a genetic condition.
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health visitor. An experienced, trained specialist nurse who monitors and advises on
child health, growth and development.
hypotonic. More floppy than usual due to changes affecting the muscles; having low
muscle tone.
menopause. Time of changes in a woman’s body, before and after her last period.
mosaic. A person who has some cells with the usual number of X chromosomes (XX),
and some cells with three X chromosomes (XXX). The effect on the person depends on
the proportion of cells with two and three X chromosomes.
period. Monthly bleeding (menstruation) in a woman.
puberty. Start of changes in the body, including increase in height, breast development
and the start of menstruation (periods).
sex chromosomes. The X chromosome and the Y chromosome. The sex
chromosomes control whether a person is male or female. Females usually have two X
chromosomes. Males usually have one X chromosome and one Y chromosome.
speech therapy. Specialist help with learning to talk, for children who start to talk late,
or who make slow progress with speaking.
sperm. The father’s contribution to the cell which will grow to form a new baby. Each
sperm contains 23 chromosomes; one from each pair in the father. An egg contains one
chromosome from each of the mother’s 23 pairs. The sperm joins with an egg to make a
complete cell. A baby develops from this first cell.
X chromosome. One of the sex chromosomes. Females usually have two X
chromosomes. Males have one X chromosome and one Y chromosome. Females
with Triple X have three X chromosomes.
XX. This represents the usual sex chromosomes of a female. Females usually have two
X chromosomes. One X chromosome is inherited from each parent. Females with
Triple X have three X chromosomes.
XY. This represents the usual sex chromosomes of a male. Males have one X
chromosome and a Y chromosome. A male inherits his X chromosome from his
mother and his Y chromosome from his father.
Y chromosome. One of the sex chromosomes. Males have one Y chromosome and
one X chromosome. Females usually have two X chromosomes.
This glossary is intended only for use by patients and families, with the genetic
information to which it refers.
This edition prepared in July 2005
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