Gonadal dysgenesis

Gonadal dysgenesis is a term used to describe multiple reproductive system development disorders. They are conditions of genetic origin. It is characterized by a progressive loss of primordial germ cells on the developing gonads of an embryo. This loss leads to extremely hypoplastic (underdeveloped) and dysfunctioning gonads mainly composed of fibrous tissue, hence the name streak gonads.

It originally referred to Turner syndrome, but use of the term has expanded to cover other conditions.

Pathogenesis
During embryogenesis, without any external influences for or against, the human reproductive system is intrinsically conditioned to give rise to a female reproductive organisation. As a result, if a gonad cannot express its sexual identity via its hormones—as in gonadal dysgenesis—then the affected person, no matter whether genetically male or female, will develop both internal and external female genitalia.

In both sexes, the commencement and progression of puberty require functional gonads that will work in harmony with the hypothalamic and pituitary glands to produce adequate hormones. For this reason, in gonadal dysgenesis the accompanying hormonal failure also prevents the development of secondary sex characteristics in either sex, resulting in a sexually infantile female appearance and infertility.

Embryology
This condition will occur if there is an absence of both Mullerian inhibiting factor and testosterone. The absence of testosterone will result in regression of the Wolffian ducts; normal male internal reproductive tracts will not develop. The absence of Mullerian inhibiting factor will allow the Mullerian ducts to differentiate into the oviducts and uterus. In sum, this individual will be genotypically male (i.e., XY), yet will possess female-like internal and external reproductive characteristics.

Causes
The condition may be due to:
 * Turner syndrome, and its variations (i.e. mosaicism)
 * XX gonadal dysgenesis, also pure gonadal dysgenesis, 46, XX
 * Swyer syndrome, also pure gonadal dysgenesis, 46, XY
 * Perrault syndrome, XX gonadal dysgenesis + sensorineural hearing loss
 * Mixed gonadal dysgenesis
 * Endocrine disruptors