Turner syndrome is a genetic disorder in females, it is due to the partial or complete loss of one of the X chromosomes. Turner syndrome is also known as monosomy of the X chromosome. Turner syndrome leads to various developmental problems and people with Turner syndrome are at risk of many diseases.
In 1938, Henry H. Turner described the condition first hence the name Turner syndrome.
Turner syndrome is the only viable monosomic chromosomal anomaly.
Turner syndrome causes retarded sexual development in females. They are mostly sterile with short stature and webbing of the skin in the neck region is present. Apart from these, there may be cardiac abnormalities, hearing impairment, vision loss, etc. may be present in a person with Turner Syndrome. There is no cure because it is a genetic disorder, but treatment may help in resolving issues such as learning difficulties, short stature and sexual development. Turner syndrome can be diagnosed by antenatal tests during pregnancy.
Turner Syndrome Causes and Types
Turner syndrome is a genetic disorder. It is due to aneuploidy of the sex chromosome. One X chromosome is missing in all the cells or some cells. Only females are born with this condition.
The occurrence of Turner syndrome is 1:2500 female births.
The turner syndrome can be due to many reasons
- Monosomy of X: This accounts for half of the Turner syndrome cases. There is a complete loss of one X chromosome. This results from the abnormal cell division during gamete formation. Eggs or sperm lack a sex chromosome. People with this type of Turner syndrome have all the cells lacking one X chromosome, i.e. they have 45 chromosomes in all the cells.
People with XO are found to have no Barr bodies, i.e. the X chromosome present is not inactivated but the active genes are required in pair for proper growth and development.
- Mosaicism: When the sex chromosome is lost during mitosis after fertilisation, i.e. during the development of the zygote, it results in some cells with 45 chromosomes (one X chromosome) and some cells having normal 46 chromosomes (XX chromosomes).
When the loss occurs during early in the development, there are a large number of cells with 45 chromosomes and they develop the symptoms of Turner syndrome.
If the loss occurs late in the development, the number of aneuploid cells are less so the severity of the symptom is reduced.
In some cases of somatic mosaics, there is a presence of 45 X cells and some cells with an extra X chromosome, i.e. 47 XXX. Girls are taller with this type of genetic constituent.
- X Chromosome abnormalities: In 20% of cases of Turner syndrome, two X chromosomes are present in the cells but one X chromosome has an abnormal structure.
This can be due to the presence of one circular shaped chromosome with joined ends known as ring chromosome.
Sometimes one X chromosome has two long arms instead of one short and one long arm known as isochromosome.
One X chromosome might be missing in some of the genetic material due to deletion.
In some females with Turner syndrome, apart from 45 X cells, there can be a small number of cells with a Y chromosome, i.e. 46 XY. This makes them at high risk of developing cancer known as gonadoblastoma.
Turner Syndrome Symptoms
The symptoms of Turner syndrome vary according to the genetic makeup of an individual. Mostly they are females with rudimentary ovary so they are sterile and have short stature.
Main symptoms of Turner syndrome include:
- Common facial features such as drooping eyelids, narrow palate, small jaws and low-set prominent earlobes
- Growth is irregular, no regular growth spurts and puberty is delayed
- Short stature as compared to other females
- Female may have normal intelligence and good reading and verbal skills but may have some learning difficulties, e.g. difficulty in memorising, difficulties in learning math and spatial concepts
- They might find difficulty in non-verbal communication and understanding of other’s emotions
- Poorly developed breasts, delayed or no onset of the menstrual cycle and infertile
- Murmuring of heart due to narrowing aorta and other abnormalities related to heart, liver and kidney
- Hypothyroidism and hypertension is frequent
- Insufficient estrogen leads to osteoporosis
- Chronic middle ear infection leading to hearing loss
Symptoms of Turner syndrome can be seen in the developing foetus also:
- Lymphedema is characterised by swelling due to excess fluid leaking in the body
- Swelling or thickness of the neck
- Lower than normal weight
Turner Syndrome Diagnosis
Turner syndrome can be diagnosed during pregnancy in ultrasound or by specific tests like amniocentesis to find out the karyotype of the foetus.
At birth, Turner syndrome can be diagnosed by swelling in hands and feet, heart or kidney problems, webbed neck, broad chest with widely placed nipples.
Sometimes Turner syndrome is not diagnosed until the adolescence stage when puberty does not occur.
Turner Syndrome Treatment
There is no cure for Turner syndrome. Whatever treatment is done, it is for complications related to Turner syndrome such as sexual development, hearing and vision impairment, infertility.
Preventive care can keep conditions such as heart complications and thyroid under check.
Hormone therapy is useful for short stature, inducing sexual development and reducing the risk linked to it.
IVF can help if a female with Turner syndrome wishes to get pregnant.
Learning difficulties can be overcome with proper training and educational support.