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Gonadal Dysgenesis: Causes of Swyer and Turner Syndrome

General Definition:

Gonadal dysgenesis is a congenital developmental disorder of the gonads: the gonads lack parts of the reproductive and hormone-active tissue, this is replaced with connective tissue. The maximum variant of gonadal dysgenesis are streak gonads without any significant hormone production or reproductive tissue.

Causes and Symptoms of Gonadal Dysgenesis

Turner Syndrome:

Turner syndrome results in females with gonadal dysgenesis due to a missing or non-functioning X chromosome (monosomy 45,X, various mutations/arm losses on the X chromosome at 46,XX or mosaic 45,X/46,XX). Leading symptoms are lack of sexual development and a very small body size (133 to 153 cm). Typical external physical anomalies are lymphedema of extremities and nuchal fold (pterygium colli) after birth, micrognathia, epicanthus folds, low ear base, and fassthorax. Malformations of internal organs are common (aorta, heart, urinary tract).

Therapy consists in hormone substitution: to increase height, high-dose therapy with growth hormones for several years is necessary. The therapeutic gain is about 10 cm in 3–7 years. Estrogen and progesterone substitution from puberty onwards ensures development of secondary sexual characteristics and may enable a menstrual cycle.

46,XY gonadal dysgenesis (Swyer syndrome):

Swyer syndrome causes a female phenotype with normal development until puberty, normal body size, bilateral gonadal dysgenesis with streak gonads, elevated gonadotropins, and missing onset of puberty and sexual development. The cause is mutations of the Y chromosome, more specifically of the SRY gene or other downstream genes necessary for SRY action. In case of large arm losses of the Y chromosome, additional stigmata of Turner syndrome are present.

Cyclic estrogen and progesterone substitution from puberty onwards ensures sexual development. There is a high risk (30%) for a malignant gonadal tumor after puberty, prophylactic removal of the gonads due to the tumor risk is recommended.

46,XX gonadal dysgenesis:

46,XX gonadal dysgenesis is a rare form of congenital primary ovarian failure, caused by isolated gene defects on the X chromosome. The symptoms and therapy correspond to those of 46,XY gonadal dysgenesis, but surgical removal of the gonads is unnecessary due to low tumor risk.

45,X/46,XY mixed gonadal dysgenesis:

45,X/46,XY mixed gonadal dysgenesis is a mosaic with 45,X and 46,XY, the resulting phenotype is variable and depends on the extent of Y chromosome function. Symptoms are asymmetric gonads (unilateral testis with contralateral streak gonad), variable incomplete masculinization, urogenital sinus with uterus and vagina. Physical stigmata of Turner syndrome are possible. The risk of Wilms tumor is increased (Denys-Drash syndrome). Treatment options during puberty include hormone replacement to support the desired gender role, sex reassignment surgery if necessary, and prophylactic removal of the gonads due to the tumor risk.

References

C. Radmayr, G. Bogaert, H. S. Dogan, and Tekg&uuml, “EAU Guidelines: Paediatric Urology,” 2022. [Online]. Available: https://uroweb.org/guidelines/paediatric-urology/.

  Deutsche Version: Gonadale Dysgenesie, Turner-Syndrom und Swyer-Syndrom