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2010-06-25-12 Monosomy X © Davidkov

Monosomy X

Mario Davidkov, MD, PhD.

Private Clinic of Obstetrics and Gynecology, Varna, Bulgaria.


Turner syndrome (Monosomy X)

Genetic disorder caused by partially or completely missing X chromosome. The disorder causes short stature, infertility, and characteristic facial, head and neck features and may also cause cardiac, endocrine and kidney abnormalities. Turner syndrome only affects females.                                                                                                                             
Turner syndrome was named after Dr. Henry H. Turner, an endocrinologist who described this condition in 1938. He noticed similarities between number of patients between ages 15 to 23, who were referred for dwarfism and lack of sexual development. The X chromosomal abnormality was not described until thirty years later.


Turner syndrome occurs in about 5: 10,000 live births.


About half of individuals with Turner syndrome have monosomy X, which means each cell in the individual's body has only one copy of the X chromosome instead of the usual two copies. In monosomy X, the chromosomal abnormality occurs as a random event during the formation of reproductive cells (eggs and sperm). An error in cell division called nondisjunction can result in reproductive cells with an abnormal number of chromosomes. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have a single X chromosome in each cell and will be missing the other sex chromosome.

Some women with Turner syndrome have a chromosomal changes in only some of their cells, which is known as mosaicism. Mosaic Turner syndrome is not inherited, but occurs as a random event during cell division in early fetal development. As a result, some of the affected cells have the usual two sex chromosomes and other cells have only one copy of the X chromosome.

Researchers have not determined which genes on the X chromosome are responsible for most of the features of Turner syndrome. They have, however, identified one gene called SHOX that is important for bone development and growth. Missing one copy of this gene likely causes the short stature and skeletal abnormalities in women with Turner syndrome. The X chromosome abnormality may occur as a random event during the formation of reproductive cells (monosomy X) or may be inherited.                                 

Signs and symptoms

Turner syndrome can present as a variety of signs and symptoms.
Structural abnormalities include: Flat, broad chest, webbed neck; low set ears; retrognathia; narrowing of the aorta, high arched palate; flat feet, scoliosis, rudimentary ovaries.


Turner syndrome may  be diagnosed in utero performing amniocentesis or chorionic villus sampling. Fetuses with Turner syndrome can be identified by abnormal ultrasound findings which are characteristic for this condition (i.e. heart defect, kidney abnormality, cystic hygroma, ascites).

Symptoms in sonography: A substantial proportion of fetuses with Turner syndrome shows early-onset signs that could be detected in the first trimester. The most common findings are: cystic hygroma, fetal hydrops, cardiac defects and increased nuchal translucency. Among heart defects, coarctation of the aorta is the most common (44.4% of all cardial defects).

Although the recurrence risk is not increased, genetic counseling is often recommended for families who have had a pregnancy or child with Turner syndrome.

Case report 1

Primigravida came to our department at 15 weeks of gestation. She had non-contributive family or personal history. We have seen cystic hygroma and fetal hydrops. The amniocentesis result showed monosomy X, 45 X0. The pregnancy was terminated afterwards.

Images 1,2: Image 1 shows a transverse view of the fetal neck showing cystic hygroma. Image 2 shows a 3D image of the cystic hygroma (note the arrow). Note deformities of the occipital and parietal bones.

Images 3,4: 3D images showing flat profile and cystic hygroma.

Images 5: Transverse view of the fetal thorax, note the hydrops.

Video 1- 4: Videos of the cystic hygroma and fetal hydrops, note flat profile of the fetus.

Case report 2

This is a case of pregnancy after in vitro fertilization (IVF). We examined the patient at 18 weeks of gestation. There was a large cystic hygroma of the neck and decreased amount of the amniotic fluid. The amniocentesis results confirmed our diagnosis, 45 X0.
Patient's consecutive pregnancy was also after IVF. This time, it was a twin pregnancy after two embryos transfer. At 17 weeks of gestation the female fetus showed all the ultrasound signs typical for Turner syndrome: cystic hygroma, hydrops. The fetus died in utero shortly after ultrasound examination. Patient delivered a healthy term boy. Placental examination showed fetus papyraceus, remnant of the affected twin.

Images 6,7,8: Image 6 shows a transverse view of the fetal neck with large cystic hygroma. Images 7,8 show 3D images of the fetal hygroma.

Images  9,10: Pictures of the fetus after pregnancy termination, note cystic hygroma.


1. Papp C, Beke A, Mezei G, Szigeti Z, Bán Z, Papp Z. Prenatal diagnosis of Turner syndrome: report on 69 cases. J Ultrasound Med. 2006 Jun; 25(6): 711-7; quiz 718-20.
2. Kaneko N, Kawagoe S, Hiroi M (1990). "Turner's syndrome--review of the literature with reference to a successful pregnancy outcome". Gynecol Obstet Invest.
3. Sybert VP, McCauley E (September 2004). "Turner's syndrome". N. Engl. J. Med. 351 (12): 1227–38.


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