Triple X syndrome
Encyclopedia
Triple X syndrome is a form of chromosomal
variation characterized by the presence of an extra X chromosome
in each cell
of a human female
. The condition always produces females, with an XX pair of chromosomes, as well as an additional chromosome, resulting in the formation of XXX. A mosaic form also occurs where only a percentage of body cell contain XXX while the remainder carry XX. The extent to which an individual is affected by the condition will depend upon the proportion of XXX to XX throughout. The condition is also known as triplo-X, trisomy X, XXX syndrome, and 47,XXX aneuploidy. Triple X results during division of a parent's reproductive cells and occurs about once in every 1,000 female births. Unlike most other chromosomal conditions (such as Down syndrome), there is usually no distinguishable difference to the naked eye between women with triple X and the rest of the female population.
Triple X syndrome is not inherited, but usually occurs as an event during the formation of reproductive cells (ovum
and sperm
). An error in cell division called nondisjunction
can result in reproductive cells with additional chromosomes. For example, an oocyte
or sperm cell may gain an extra copy of the X chromosome as a result of the non-disjunction. If one of these cells contributes to the genetic makeup of a child, the child will have an extra X chromosome in each of her cells. In some cases, trisomy X occurs during cell division in early embryo
nic development.
Some females with triple X syndrome have an extra X chromosome in only some of their cells. These cases are called 46,XX/47,XXX mosaic
s.
, in all female cells, only one X chromosome
is active at any time. Thus, Triple X syndrome most often causes no unusual physical features or medical problems. But there are rare cases when a female with Triple X syndrome is affected by changes such as tall stature, behavioral problems, clumsiness, poor coordination, midfacial hypoplasia
, wide-set eyes, epicanthic fold, amenorrhea, posteriorly rotated ears, small head, long head, small lower jaw, expressionless face, prominent forehead, enamel hypoplasia
, widely spaced nipples, small hands, small feet, kyphosis
, lordosis
, reduced muscle tone, ovarian failure, mental retardation
, and infertility
. Females with the condition may have menstrual irregularities and, although rarely exhibiting severe mental impairments, have an increased risk of learning disabilities, delayed speech, deficient language skills and delayed development of motor skills.
There are seldom any observable physical anomalies in Triple X females, other than being taller than average. Most women with Triple X have normal sexual development. Some experience an early onset of menstruation
. Triple X women are rarely diagnosed, apart from pre-natal testing methods, unless they undergo amniocentesis
and blood tests for medical reasons later in life. Most medical professionals do not regard the condition as a disability
. However, if mild delays are present, such status can be sought by parents for early intervention treatment
.
each day.
, et al. at Western General Hospital
in Edinburgh, Scotland, in 1959. It was found in a 35‑year-old, 5 ft. 9 in. (176 cm) tall, 128 lb. (58.2 kg) woman who had premature ovarian failure
at age 19; her mother was age 41 and her father was 40 at the time of her conception.
between 1970-1984 76% of the prenatally diagnosed fetuses with triple-X were aborted. Between 1985-1987 this figure dropped to 56%. With improved information the number of abortions diminished. The experience in the Netherlands
demonstrates that during the period 1991-2000 33% (18/54) of the couples that were confronted with a prenatal diagnosis of 47,XXX elected to abort. If balanced information is provided to prospective parents, pre-natally, the incidence of voluntary termination (abortion) is reduced.
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
variation characterized by the presence of an extra X chromosome
X chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
in each cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
of a human female
Woman
A woman , pl: women is a female human. The term woman is usually reserved for an adult, with the term girl being the usual term for a female child or adolescent...
. The condition always produces females, with an XX pair of chromosomes, as well as an additional chromosome, resulting in the formation of XXX. A mosaic form also occurs where only a percentage of body cell contain XXX while the remainder carry XX. The extent to which an individual is affected by the condition will depend upon the proportion of XXX to XX throughout. The condition is also known as triplo-X, trisomy X, XXX syndrome, and 47,XXX aneuploidy. Triple X results during division of a parent's reproductive cells and occurs about once in every 1,000 female births. Unlike most other chromosomal conditions (such as Down syndrome), there is usually no distinguishable difference to the naked eye between women with triple X and the rest of the female population.
Cause
Triple X syndrome is not inherited, but usually occurs as an event during the formation of reproductive cells (ovum
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
and sperm
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
). An error in cell division called nondisjunction
Nondisjunction
Nondisjunction is the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2. This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a...
can result in reproductive cells with additional chromosomes. For example, an oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
or sperm cell may gain an extra copy of the X chromosome as a result of the non-disjunction. If one of these cells contributes to the genetic makeup of a child, the child will have an extra X chromosome in each of her cells. In some cases, trisomy X occurs during cell division in early embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic development.
Some females with triple X syndrome have an extra X chromosome in only some of their cells. These cases are called 46,XX/47,XXX mosaic
Mosaic (genetics)
In genetic medicine, a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one individual who has developed from a single fertilized egg...
s.
Symptoms
Because of the lyonization, inactivation and formation of a Barr bodyBarr body
A Barr body is the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y or W chromosome rather than the diploidy of the X or Z...
, in all female cells, only one X chromosome
X chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
is active at any time. Thus, Triple X syndrome most often causes no unusual physical features or medical problems. But there are rare cases when a female with Triple X syndrome is affected by changes such as tall stature, behavioral problems, clumsiness, poor coordination, midfacial hypoplasia
Hypoplasia
Hypoplasia is underdevelopment or incomplete development of a tissue or organ. Although the term is not always used precisely, it properly refers to an inadequate or below-normal number of cells. Hypoplasia is similar to aplasia, but less severe. It is technically not the opposite of hyperplasia...
, wide-set eyes, epicanthic fold, amenorrhea, posteriorly rotated ears, small head, long head, small lower jaw, expressionless face, prominent forehead, enamel hypoplasia
Enamel hypoplasia
Enamel hypoplasia is the defect of the teeth in which the tooth enamel is hard but thin and deficient in amount. This is caused by defective enamel matrix formation with a deficiency in the cementing substance....
, widely spaced nipples, small hands, small feet, kyphosis
Kyphosis
Kyphosis , also called roundback or Kelso's hunchback, is a condition of over-curvature of the thoracic vertebrae...
, lordosis
Lordosis
Lordosis is a medical term used to describe an inward curvature of a portion of the lumbar and cervical vertebral column. Two segments of the vertebral column, namely cervical and lumbar, are normally lordotic, that is, they are set in a curve that has its convexity anteriorly and concavity...
, reduced muscle tone, ovarian failure, mental retardation
Mental retardation
Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
, and infertility
Infertility
Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to full term...
. Females with the condition may have menstrual irregularities and, although rarely exhibiting severe mental impairments, have an increased risk of learning disabilities, delayed speech, deficient language skills and delayed development of motor skills.
There are seldom any observable physical anomalies in Triple X females, other than being taller than average. Most women with Triple X have normal sexual development. Some experience an early onset of menstruation
Menstruation
Menstruation is the shedding of the uterine lining . It occurs on a regular basis in sexually reproductive-age females of certain mammal species. This article focuses on human menstruation.-Overview:...
. Triple X women are rarely diagnosed, apart from pre-natal testing methods, unless they undergo amniocentesis
Amniocentesis
Amniocentesis is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amnion or amniotic sac surrounding a developing fetus, and the fetal DNA is examined for...
and blood tests for medical reasons later in life. Most medical professionals do not regard the condition as a disability
Disability
A disability may be physical, cognitive, mental, sensory, emotional, developmental or some combination of these.Many people would rather be referred to as a person with a disability instead of handicapped...
. However, if mild delays are present, such status can be sought by parents for early intervention treatment
Therapy
This is a list of types of therapy .* Adventure therapy* Animal-assisted therapy* Aquatic therapy* Aromatherapy* Art and dementia* Art therapy* Authentic Movement* Behavioral therapy* Bibliotherapy* Buteyko Method* Chemotherapy...
.
Incidence
Triple X syndrome occurs in around 1 in 1,000 girls. On average, five to ten girls with triple X syndrome are born in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
each day.
First case
The first published report of a woman with a 47,XXX karyotype was by Patricia A. JacobsPatricia Jacobs
Patricia Ann Jacobs FRS FMedSci is a British geneticist, fellow of the Royal society. She is Professor of Human Genetics in University of Southampton at Salisbury District Hospital...
, et al. at Western General Hospital
Western General Hospital
The Western General Hospital , at Crewe Road, Edinburgh, Scotland is part of NHS Lothian, a Heath Board which provides a comprehensive range of adult and paediatric care to the people of Edinburgh, the Lothians and beyond.It is one of the main teaching hospitals affiliated to the University of...
in Edinburgh, Scotland, in 1959. It was found in a 35‑year-old, 5 ft. 9 in. (176 cm) tall, 128 lb. (58.2 kg) woman who had premature ovarian failure
Premature ovarian failure
Premature Ovarian Failure , also known as premature ovarian insufficiency, primary ovarian insufficiency , premature menopause, hypergonadotropic hypogonadism, is the loss of function of the ovaries before age 40...
at age 19; her mother was age 41 and her father was 40 at the time of her conception.
Statistics
In DenmarkDenmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
between 1970-1984 76% of the prenatally diagnosed fetuses with triple-X were aborted. Between 1985-1987 this figure dropped to 56%. With improved information the number of abortions diminished. The experience in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
demonstrates that during the period 1991-2000 33% (18/54) of the couples that were confronted with a prenatal diagnosis of 47,XXX elected to abort. If balanced information is provided to prospective parents, pre-natally, the incidence of voluntary termination (abortion) is reduced.
See also
- Klinefelter syndrome
- XYY syndromeXYY syndromeXYY syndrome is an aneuploidy of the sex chromosomes in which a human male receives an extra Y-chromosome, giving a total of 47 chromosomes instead of the more usual 46. This produces a 47,XYY karyotype...
- Turner syndromeTurner syndromeTurner syndrome or Ullrich-Turner syndrome encompasses several conditions in human females, of which monosomy X is most common. It is a chromosomal abnormality in which all or part of one of the sex chromosomes is absent...
- XXXX syndromeXXXX syndromeXXXX syndrome is a rare chromosomal disorder caused by the presence of four X chromosomes instead of two X chromosomes. This condition occurs only in females, as there are no Y chromosomes present. Tetrasomy X was first described in 1961, and since then approximately 100 cases have been reported...
- XXXXX syndromeXXXXX syndromeXXXXX syndrome is the presence of three additional X chromosomes. Diagnosis is done by karyotyping. Approximately 25 females have been described in medical literature worldwide with this extremely rare condition. The condition was first described in 1963...
External links
- NLMUnited States National Library of MedicineThe United States National Library of Medicine , operated by the United States federal government, is the world's largest medical library. Located in Bethesda, Maryland, the NLM is a division of the National Institutes of Health...
(2007). Triple X syndrome Genetics Home Reference - Guy's HospitalGuy's HospitalGuy's Hospital is a large NHS hospital in the borough of Southwark in south east London, England. It is administratively a part of Guy's and St Thomas' NHS Foundation Trust. It is a large teaching hospital and is home to the King's College London School of Medicine...
Clinical Genetics Department (2001). Triple X information leaflet - Nielsen, Johannes (1998). Triple-X Females. An Orientation. The Turner Center, AarhusAarhusAarhus or Århus is the second-largest city in Denmark. The principal port of Denmark, Aarhus is on the east side of the peninsula of Jutland in the geographical center of Denmark...
Psychiatric Hospital, RisskovRisskovRisskov is one of the most affluent areas in Denmark, and a district to the city of Aarhus. The name literally means The Forest of Riis, as described on the memorial stone marking the entrance to the area.-Origin of name and history of Riis Skov:...
, DenmarkDenmarkDenmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
.- Triple X information booklet by Dr. Nielsen, a psychiatrist and geneticist who led the longest running of 8 international newborn screening studies of sex chromosome abnormalities.