Turner Syndrome

Turner syndrome is a genetic disease in females, caused by the loss of an X chromosome. In 1938, Henry H. Turner first observed the condition. Like all other genetic disorders, Turner Syndrome has no cure, but lifestyle quality can be improved through special care for the affected individuals.

Causes of Turner Syndrome

Aneuploidy is the condition in which there is a variation in the number of chromosomes that results in the addition or loss of one or more chromosomes. The aneuploidy related to the loss of one chromosome to an otherwise diploid genome is known as monosomy, depicted as (2n−1) complement.

Monosomy of the X chromosome is the only viable monosomic aberration that causes Turner Syndrome (designated 45, XO) in females. In the full 45, X individuals, a Barr body is absent. In mosaic cases (some 46, XX cells present), a Barr body may be present in the 46, XX cells. Turner Syndrome is found in approximately 1 infant in every 2000 live female births; most of the (45, XO) foetuses die in utero and are aborted spontaneously.

Nondisjunction of the X Chromosome

The shortage of an X chromosome exists due to the nondisjunction of the X chromosome during meiosis.
Nondisjunction happens when the paired homologs of X chromosomes fail to disjoin and segregate properly during Anaphase I or Anaphase II of meiosis, during gamete formation.
It led to the formation of gametes containing the atypical chromosome composition like (n+1) or (n−1).
Subsequent fertilisation of the (n−1) chromosome containing gamete with a normal one results in the monosomic condition.

Mosaicism in Turner Syndrome

During early development, nondisjunction might occur during the mitotic division in the zygote, resulting in two different cell lines: some normal cells with 46 chromosomes and some cells with the monosomy of X. If the error occurs late in the development, the number of cells with monosomic aberration is less in number, reducing the severity of the symptom. The affected individuals show a mixture of karyotypes and exhibit varying aspects of Turner Syndrome.

Some individuals have cell lines containing Y-chromosome material (e.g., mosaic 45,X/46,XY). The presence of Y material increases the risk of gonadoblastoma (a type of cancer).

In some cases, two X chromosomes are present in the cells, but one has an abnormal structure due to the presence circular-shaped ring chromosome or deletion of segments.

Effects of Turner Syndrome

Affected individuals have female external genitalia and internal ducts, but their ovaries are rudimentary.
Primary amenorrhea (absence of menarche) and ovarian failure are common. Most affected women are infertile without assisted reproduction.
Osteoporosis due to insufficient oestrogen level.
A broad shield-like chest with underdeveloped breasts.
Skin folds on the back of the neck.
Average intelligence with some cognitive impairment; faces difficulties in memorising and learning numerical or spatial concepts.
Short stature is typical. It is largely because the pubertal growth spurt is absent or diminished. (Final adult height is reduced unless treated with growth hormone.)
Aortic narrowing due to a recognised cardiac lesion in Turner syndrome. It can cause hypertension and heart murmurs and requires cardiology evaluation.
Chronic middle ear infections.
Hypothyroidism.
Hypertension.
Typical craniofacial features include micrognathia (small jaw), low-set ears, high-arched (narrow) palate, and low posterior hairline.

Prenatal diagnosis is possible (CVS or amniocentesis), and some cases are detected antenatally. Many affected individuals are also first recognised in childhood/adolescence due to short stature or delayed puberty.

Treatment for Turner Syndrome

Turner syndrome does not have a cure. The treatments available treat the complications related to the syndrome.
Cardiac complications and thyroid issues are dealt with through preventive care.
Growth hormone therapy for short stature.
Estrogen replacement (often followed by cyclic progesterone) is used to induce/maintain secondary sexual development and protect bone health.
Spontaneous pregnancy is rare. Pregnancy is possible with assisted reproduction using donor oocytes and IVF. But it carries increased maternal cardiovascular risk and requires thorough cardiac evaluation and specialist care.
Proper training and support for learning disabilities.

Frequently Asked Questions (FAQs)

Q1. Can girls with Turner Syndrome live a normal lifespan?

Yes. With proper medical care for heart, thyroid, and hormonal health, most individuals with Turner Syndrome can live a normal lifespan.

Q2. Is Turner Syndrome inherited from parents?

No. Turner Syndrome usually occurs due to a random error (nondisjunction) during the formation of reproductive cells. It is generally not passed down from parents.

Q3. Can women with Turner Syndrome become pregnant?

Most women with Turner Syndrome are infertile, but pregnancy is possible with donor eggs and IVF, though it carries increased health risks that must be closely monitored by specialists.