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Sexual Differentiation : Gonadal Dysgenesis

Gonadal dysgenesis is characterized by Turner's syndrome in which women preset with an XO karyotype, short stature (mean adult height 141 + 0.6 cm), primary amenorrhea, streak gonads, and sexual infantilism. Other physical findings associated with classical forms of gonadal dysgenesis include: epicanthal folds, high arched palate, low nuchal hairline, webbed neck, shield chest, coarctation of the aorta, ventricular septal defect, renal anomalies, pigmented nevi, nail hypoplasia, cubitus valgus, and short fourth metacarpal. Hypertension is relatively common in adults with the disorder. They also frequently have autoimmune thyroid disorders (Hashimotos thyroiditis).

Turner's Synd
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Turner's Syndrome. Females with a 45,XO karyotype characteristically have short stature, primary amenorrhea, streak gonads, and sexual infantilism.
Credits: Adapted with permission from Jaffe R.B. Disorders of Sexual Development. In Yen S.S.C. and Jaffe R.B. eds Reproductive Endocrinology, W. B. Saunders Co., Philadelphia, 1986, p 287.

The disorder is a result of accelerated oocyte atresia in which these women under go menopause before they enter puberty. Both X chromosomes are required for female germ cell survival. Because of oocyte atresia ovarian development is altered and sex steroid secretion is deficient resulting in elevated FSH levels consistent with menopause. Additionally, the deficiency of the X chromosome results in abnormalities of skeletal structures; epiphyses, teeth, and skull. These patients also have an unusual cognitive defect which renders them unable to appreciate the shapes and relationships of objects to each other (space-form blindness). While Turner's syndrome (45, X) is the sine quo non of gonadal dysgenesis and is the chromosomal-complement found by pediatricians in 80% of young women manifesting these signs and symptoms, only 40% of women presenting with primary amenorrhea have the 45,X complement. The remainder are divided between 46,XX or 46,XY (40%) or X-chromosome structural abnormalities or mosaicism (20%). Approximately 20-30% of patients with 46,XY gonadal dysgenesis develop a dysgerminoma or gonadoblastoma, therefore gonads should be removed from individuals with 46,XY gonadal dysgenesis.