The prevalence of Turner syndrome is 1:2500 female births. Turner syndrome consists of approximately 2% of all conceptions and 20% of all miscarriages. Approximately 98-99% of the fetuses with this condition are spontaneously aborted, 75% are aborted between 12-40 weeks and 50% between 16 and 40 weeks. Turner syndrome is not associated with advanced maternal age and the recurrence risk is not increased over the general population risk. Only in 50% of the children with Turner syndrome is the karyotype 45,X. In about 15% of the cases, isochromosome X is detected and 40% of the cases are mosaic (45,X/46,XX and 45,X/46,XY). Patients with mosaicism tend to have milder manifestation. Hall et al noted that 1/3 of the cases are diagnosed in the newborn period, 1/3 in childhood and 1/3 during puberty due to amenorrhea and failure to develop secondary sexual characteristic.
The most common prenatal ultrasound findings include cystic hygroma, hydrops fetalis, cardiac abnormalities and renal abnormalities, mainly horseshoe kidney. Of the fetuses with cystic hygroma detected during the first trimester of pregnancy, about 20% have 45,X. However, in the second trimester of pregnancy, 40% of the cases detected with cystic hygroma have 45,X karyotype. In the newborn period, the major clinical manifestations include dysmorphic facial features with epicanthic folds, ptosis, hypoplasia of the malar areas, prominent ears and retrognathia. The neck is short and webbed with low nuchal hairline, the internipple distance is increased and there is a broad chest. Coarctation of the aorta occurs in about 50% of the cases with 45,X and 15% of the cases with other chromosome abnormalities associated with Turner syndrome. Less common cardiac anomalies include bicuspid aortic valve, VSD, ASD and hypoplastic left heart. Lymphoedema, usually transient in childhood, occurs in about 80% of the newborns and is mainly noted on the hands and feet. In some, the lymphoedema recurs. Renal abnormalities, mainly in the form of horseshoe kidney occur in 20% of the newborns and other renal abnormalities are seen in 20% of the cases. Obstructive uropathy with oligohydramnios, Potter sequence and cystic dysplasia have also been reported. Gonadal dysgenesis or streak gonads are characteristic but usually develop after infancy. Skeletal findings include cubitus valgus, short fourth metacarpals, hypoplasia of the cervical vertebrae. Without hormone therapy, the bone age remains delayed and osteopenia develops. Hypothyroidism, diabetes mellitus, and autoimmune thyroiditis are common. Maternal serum screening between 15 and 18 weeks gestation was found positive for Down syndrome in Turner syndrome associated with hydrops fetalis, with both human chorionic gonadotropin and estriol contributing.
Cystic hygroma can be associated with other chromosome abnormalities including trisomy 21, 13 and 18. It is also associated with single gene disorders including autosomal dominant cystic hygroma/pterygium colli, Noonan syndrome, achondroplasia, lethal multiple pterygium syndrome, Roberts syndrome, Cumming syndrome, Cowchock syndrome and achondrogenesis type II among others. Short stature can be seen in Noonan syndrome, familial short stature, growth hormone deficiency, hypothyroidism, multiple pterygium syndrome, prenatal exposure to teratogens such as alcohol and due to chronic condition. Lymphoedema can be seen in Milroy syndrome, lymphoedema with distichiasis, Hennekam syndrome, and lymphoedema with intestinal lymphangiectasis.
Non-immune hydrops fetalis