Turner syndrome is one of the most common chromosomal disorders with an incidence of 1:2,500 in female newborns and an estimated 1:100 conceptions (98% of these pregnancies end in miscarriage in the 1st trimester). Prenatal ultrasound may reveal early hygroma colli or hydrops fetalis which often leads to invasive prenatal screening and detection of the chromosomal disorder. The clinical manifestations are short stature (approximately 150 cm), primary amenorrhea, streak gonads, a webbed neck and slight facial dysmorphic signs such as outwardly sloping eyelids. Intelligence is within the normal range. Prenatally, dilatation of the lymphatic vessels with lymphedema and cystic hygroma is common. Hormone treatment is necessary for the development of secondary sexual characteristics. Although there is no growth hormone deficiency, growth in many patients can be improved by supplementary growth hormone therapy. Where there is 45,X/46,XY mosaicism, sonographic monitoring of the gonads is recommended due to an increased risk of gonadoblastoma. Noonan syndrome should be considered as the primary differential diagnosis.
In about 55% of patients, a complete monosomy X is present, whereas in the remaining patients, there are gonosomal mosaics or X-linked structural anomalies.
Boucher et al. 2001, J Med Genet 38:591 / Ogata et al. 2001, J Med Genet 38:1 / Wieacker 2001, Medgen 13:3 / Tarani et al. 1998, Gynecol Endocrinol 12:83 / Swillen et al. 1993, Genet Counsel 4:7