Definition: Chromosomal disorder of female patients, described by Turner in 1938[1], characterized by the absence of one X sex chromosome (45,X0).

Synonym: Monosomy X, Ullrich-Turner syndrome[2].

Incidence: 2.5-5.5: 10,000 live birth females in Caucasian population. In Japanese population it has been estimated to be 7-21: 10,000 live birth females7. The incidence in all pregnancies however, is considered much higher since Turner syndrome accounts for one fourth of the spontaneous abortions caused by chromosomal anomalies[3].

Etiology: Absence of one sex chromosome, in general the paternal chromosome which occurs sporadically in most cases. 8-16% of all cases are mosaic. Advanced maternal age is not associated with this aneuploidy.

Recurrence risk: Considering that Turner syndrome is a sporadic event in the majority of the cases, chances of recurrence are extremely low, although not precisely known.

Diagnosis: Cystic hygroma is the most characteristic prenatal feature in this syndrome. In general, the finding is consistent with a large septated cystic mass posterior to the neck (fig. 1-2), caused by abnormal connections of the lymphatic circulation. Spontaneous remission of the cyst may occur, resulting in many cases in webbing of the neck. Other common findings include lymphedema, in particular of the dorsum of hands and feet or in the more severe cases anasarca, hydrops, short cervical spine, intrauterine growth retardation, short neck, prominent auricles, horseshoe kidney, heart defects (coarctation and bicuspid aortic valve), bone dysplasia, and short stature (fig. 3). Dysgenesis of the ovaries occurs in 90% of cases, causing absent menses and infertility in adult life. Variable degrees of mental and developmental retardation are also frequently seen[4].  Elevated maternal serum beta hCG has been reported in association with Turner syndrome[5].

Figure 1: Sagittal view of the neck demonstrate large septated masses.

Figure 2: Axial view of the neck demonstrate large septated masses.

Figure 3: The fetus at autopsy.

Differential Diagnosis: Head and neck cystic mass such as cephalocele and meningocele must be excluded. Usually these conditions are associated with hydrocephalus, cranial and spine defects. Often the angle of junction of the cystic mass with skin can be used in the differential diagnosis. Cystic hygroma that lift the subcutaneous tissues tend to have smooth junction angle, while cephaloceles that herniate through the skin tend to have acute angle of junction.

Cystic hygroma may occasionally be present in Robert's syndrome, and other autosomal recessive disorders2^{, [6]} Chromosomal analysis can exclude these conditions.

Genetic anomaly: Absence or structural abnormalities of one X chromosome, such as deletion of the sex-determining region (XY Yp deletion) or mosaicism (45,X/ 46,XX or 45X/ 46XY) can also be responsible for this condition[7].

Prognosis: Intrauterine demise occurs in many cases in general caused by hydrops, which is the major intrauterine complication. Among survivors, the prognosis will depend basically on the severity of the associated anomalies. Mosaics tend to have a better prognosis, and some cases with discrete manifestations  the syndrome remains undiagnosed for years[8].

Management: A karyotype is recommended when Turner syndrome is suspected. Termination of pregnancy can be offered before viability.  After viability, standard prenatal care is not altered.

References:

[1]  Turner HH. A syndrome of infantilism, congenital webbed neck, and cubitus valgus. Endocrinology, 23: 566 (1938).

[2] Blagowidow N, Page DC, Huff D, Mennuti MT. Ullrich-Turner syndrome in an XY female fetus with deletion of the sex-determining portion of the Y chromosome. Am. J. Med. Genet. 34: 159-162 (1989)

[3] Robinow M, Spisso K, Buschi AJ, Brenbridge ANAG. Turner syndrome: sonography showing fetal hydrops simulating hydramnios. AJR 135: 846-848 (1980)

[4] Jones KL. X0 syndrome ( Turner syndrome) in Smith’s Recognizable Patterns of Human Malformation.  WB Saunders Company – Philadelphia – 81-87 (1997)

[5] Laundon CH, Spencer K, Macri JN, Anderson RW, Buchanan PD. Free beta hCG screening of hydropic and non-hydropic Turner syndrome pregnancies. Prenat Diagn. 16: 853-856 (1996)

[6] Brown BSJ, Thompson DL. Ultrasonographic features of the fetal Turner syndrome. J Can. Assoc. Radiol., 35(1): 40-46 (1984)

[7] Gravholr CH, Juul S, Naeraa RW, Hansen J. Prenatal  and postnatal prevalence of Turner’s syndrome: a registry study. BMJ 312: 16-21(1996)

[8] Koeberl DD, McGillivray B, Sybert VP. Prenatal diagnosis of 45,X/46XX mosaicism and 45,X: implications for postnatal outcome. Am. J. Hum. Genet., 57: 661-666 (1995)