Turner Syndrome Causes, Symptoms And Karyotypes
Turner syndrome is defined by the presence of a single X chromosome (sex chromosome disease, and not an autosomal disease like Down syndrome), complete or partial monosomy which is present in all cells or only in a certain proportion and associates phenotypic aspects such as nanism, defects in development of ovaries and various visceral malformations. Karyotype of this syndrome is 45x. It was noted that 15 of 1000 fetuses from recognized pregnancies are with Turner syndrome, but 99% of them are ending in miscarriage in the first trimester of pregnancy. Sexual chromatin and chromosome analysis indicate that about 1 in 2500-3000 female newborns have a 45x karyotype, so they are diagnosed with Turner syndrome.
It is estimated that the incidence of Turner syndrome, reported to all products of conception is 1% – 1.5%, Turner syndrome is one of the most common chromosomal abnormalities.
Turner Syndrome Causes
The cause for which, the majority of fetuses (95% – 99%) who are showing monosomy X, are aborted it is not known.
It concludes that monosomy X, would be lethal and that for survival would be required some degree of mosaicism. Moreover, 50% of patients with Turner syndrome, present a mosaic karyotype or structural aberrations of the second X chromosome.
It was found that 70% of cases with Turner syndrome appear as a non-mitotic disjunction with a preferential loss of the paternal X chromosome. It is estimated that half of patients with Turner syndrome present mosaics with one of the cell lines, which is having a 45X karyotype. Other cell lines may contain two X chromosomes, three X chromosomes, very rarely XY chromosomes, or may contain structural abnormalities of chromosome X or Y. Structural abnormalities of the X chromosome, occurring in 30% of cases of Turner syndrome are often of paternal origin and in this situation, paternal age can be considered a risk factor.
The clinical presentation Of Turner Syndrome (signs and symptoms)
Turner syndrome presents a clinical picture, in which the existence of certain abnormalities is leading to the recognition and diagnosis of the syndrome at birth. Phenotype becomes evident with puberty, when appear gonadal dysgenesis which amplify the clinical dysfunction.
At birth, some signs may be considered pathognomonic for Turner syndrome: lymphedema of the dorasl part of the hands and feet, short neck, dysplastic and low implanted ears, light ptosis, hypoplastic mandible, dystrophic nails and pterigium coli (webbed neck).
Since puberty, patients with Turner syndrome have short stature (150 cm in 90% of cases), which also stands in childhood (short stature after age 2-5 years), gonadal dysgenesis (fibrosis of gonads with follicles degenerate ) and absence of the installation of secondary female sexual characteristics: primary amenorrhea, mammary glands are not developt, axillary and pubic hair growth are underrepresented and infertility. It is also noted low implantation of hair, cardiovascular abnormalities of which coarctation of the aorta is the common.
Patients with Turner syndrome, often develop ear infections that can lead to deafness, also develop hypothyroidism or hyperthyroidism.
Intelligence is usually average or below average (IQ = 70-120). In patients with Turner syndrome, speech is not affected, but there is a motor deficit.
Described Karyotypes In Turner Syndrome
Turner syndrome is distinguished from other sex chromosome abnormalities, in particular from Klinefelter syndrome, by a variety of karyotype.
Besides the numerical abnormalities in Turner syndrome are structural abnormalities of one of the two X chromosomes, homogeneous or mosaic, all fitting as Turner syndrome cytogenetic varieties.
Turner syndrome cytogenetic variants and their frequency is the following::
- 45x in 53% of cases of Turner syndrome;
- Mosaicism 45x / 46XX in 15% of cases of Turner syndrome;
- X isochromosome, 46X,i(Xq) in 10% of cases of Turner syndrome;
- Mozacism 46X,i (Xq) / 46XX in 8% of cases of Turner syndrome;
- Deletions 46XXp- or 46XXq- in 6% of cases of Turner syndrome;
- Other mosaicism in 8% of cases of Turner syndrome.
Tests Used For diagnosis of Turner Syndrome
- Standrad Karyotype of peripheral blood;
- Molecular biology tests, because in 5% – 10% of cases of Turner syndrome there is an XY cell clone that can not be detected by classical cytogenetics. Such cases have an increased risk to develop gonadoblastoma and require a removal of gonadal rudiments.
The medical management of Turner syndrome:
Biosynthesised growth hormone is administered at early ages to improve the stature with 10 cm. Administration of appropriate hormonal therapy may induce the installation of menstruation. Treatment with estrogen and progesterone ensure a harmonious development, puberty and a normal sex life. This treatment prevents osteoporosis and reduces cardiovascular risks of Turner syndrome. Establishment of early therapy, allows the state of pregnancy through in vitro fertilization and birth.
Prenatal diagnosis of Turner syndrome:
Prenatal diagnosis in Turner syndrome is on the specific ultrasound signs, such as the vizualization of cystic higroma in first or second pregnancy trimester, fetal edema and highlighting the small size of the fetus. Is practice amniocentesis for fetal karyotype analysis.