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Phenotypic females with 45,X/46,XY mosaicism have a 15–30% risk of developing gonadoblastoma. Some of the patients with Turner syndrome phenotype and a Y cell line exhibit masculinization. This variant is estimated to represent approximately 6% of patients with mosaic Turner syndrome. Patients with 45,X/46,XY mosaicism can have Turner syndrome, although this form of mosaicism can also be associated with male pseudohermaphroditism, male or female genitalia in association with mixed gonadal dysgenesis, or a normal male phenotype. Guidelines for health supervision for children with Turner syndrome are published by the American Academy of Pediatrics (AAP) and include pubertal induction, as well as treatment with growth hormone and oxandrolone. They are also at increased risk for behavioral problems and deficiencies in spatial and motor perception. Most patients tend to be of normal intelligence, but intellectual disability is seen in up to 6% of affected children. These children should receive regular endocrinologic testing (see Chapter 604). There is primary amenorrhea and lack of secondary sex characteristics. The gonads are generally streaks of fibrous tissue ( gonadal dysgenesis). The most common heart defects are bicuspid aortic valves, coarctation of the aorta, aortic stenosis, and mitral valve prolapse. Congenital heart defects (40%) and structural renal anomalies (60%) are common. Older children and adults have short stature and exhibit variable dysmorphic features. It has been estimated that 95–99% of 45,X conceptions are miscarried.Ĭlinical findings in the newborns can include small size for gestational age, webbing of the neck, protruding ears, and lymphedema of the hands and feet, although many newborns are phenotypically normal ( Fig. 45,X is one of the chromosome abnormalities most often associated with spontaneous abortion. In 75% of patients, the lost sex chromosome is of paternal origin (whether an X or a Y). Turner syndrome occurs in approximately 1 in 5,000 female live births. Maternal age is not a predisposing factor for children with 45,X. The other half exhibit mosaicism and varied structural abnormalities of the X or Y chromosome. Half the patients with Turner syndrome have a 45,X chromosome complement. Turner syndrome is a condition characterized by complete or partial monosomy of the X chromosome and defined by a combination of phenotypic features ( Table 98.16). Kliegman MD, in Nelson Textbook of Pediatrics, 2020 Turner Syndrome