Ovarian dysgenesis

Gonadal dysgenesis is classified as any congenital developmental disorder of the reproductive systemin the male or female. It is the defective development of the gonads in an embryo,with reproductive tissue replaced with functionless, fibrous tissue, termed streak gonads.Streak gonads are a form of aplasia, resulting in hormonal failure that manifests as sexual infantism and infertility, with no initiation of puberty and secondary sex characteristics. Gonadal dysgenesis is classified as any congenital developmental disorder of the reproductive systemin the male or female. It is the defective development of the gonads in an embryo,with reproductive tissue replaced with functionless, fibrous tissue, termed streak gonads.Streak gonads are a form of aplasia, resulting in hormonal failure that manifests as sexual infantism and infertility, with no initiation of puberty and secondary sex characteristics. Gonadal development is a genetically controlled process by the chromosomal sex (XX or XY) which directs the formation of the gonad (ovary or testis). Differentiation of the gonads requires a tightly regulated cascade of genetic, molecular and morphogenic events.At the formation of the developed gonad, steroid production influences local and distant receptors for continued morphological and biochemical changes.This results in the appropriate phenotype corresponding to the karyotype (46,XX for females and 46,XY for males). Gonadal dysgenesis arises from the failure of signalling in this tightly regulated process during early foetal development. Manifestations of gonadal dysgenesis are dependent on the aetiology and severity of the underlying defect. 46,XX gonadal dysgenesis is characteristic of female hypogonadism with a karyotype of 46,XX. Streak ovaries are present with non-functional tissues unable to produce the required sex steroid oestrogen Low levels of oestrogen effect the HPG axis with no feedback to the anterior pituitary to inhibit the secretion of FSH and LH.FSH and LH are secreted at abnormal elevated levels. Improper levels of these hormones will cause a failure to initiate puberty, undergo menarche, and develop secondary sex characteristics.If sufficient functional ovarian tissue is present, limited menstrual cycles can occur. The pathogenesis of 46,XX gonadal dysgenesis is unclear, as it can manifest from a variety of dysregulations.Interruption during ovarian development in embryogenesis can cause 46,XX gonadal dysgenesis with cases of abnormalities in the FSH receptorand mutations in steroidogenic acute regulatory protein (StAR protein) which regulates steroid hormone production. 46,XY gonadal dysgenesis is characteristic of male hypogonadism with karyotype 46,XY. In embryogenesis, the development of the male gonads is controlled by the testis determining factor located on the sex-determining region of the Y chromosome (SRY).The male gonad is dependent on SRY and the signalling pathways initiated to several other genes to facilitate testis development.