XY type gonadal dysgenesis, trisomy X and variants

Sex determination and differentiation depend on differentiation of the indifferent gonad to the testis or ovary, which leads to masculine or feminine differentiation of internal and external genitalia. Recently, genes involved in this cascade have been identified with the advance of molecular genetical analysis. XY gonadal dysgenesis, this is a condition that has XY chromosome but is characterized by the indifferent testis. There are complete and incomplete types. Complete type has bilateral gonads of cordee, does not show physical characteristics of Turner's syndrome, has the uterus and ovaries, and has the vagina in female type, though the external genitalia are immature. Incomplete type is characterized by bilateral testicular hypoplasia(male pseudohermaphroditism) or unilateral testicular hypoplasia and bilateral restiform gonads(mixed gonadal dyspenesis), and the sexuality of the external genitalia is unclear. XX gonadal dysgenesis, complete type is characterized by bilateral restiform gonads, female type internal and external genitalia and sexual immaturity, though it does not show any characteristics of Turner's syndrome. It presents hypergonadotropic hypogonadism endocrinologically. It shows a familial incidence with autosomal recessive inheritance, and sensorineural deafness is accompanied in some cases. Incomplete type has rudimentary ovaries and show a varying degree of secondary sexual characteristics. Mixed dysgenesis, many cases have XO/XY mosaic and this dysgenesis is characterized by unilateral hypoplastic testis and contralateral restiform gonad. It may occur in cases of incomplete type XY gonadal dysgenesis. Trisomy X, cases of trisomy X have three X chromosomes as this term indicates. There are some cases of polisomy with four or more X chromosomes. The frequency of trisomy X has been reported to be one in 1,000 births of female, which means that it is a relatively common chromosomal aberration. It has been reported that about 20% of cases of trisomy X have sexual dysfunction, predominantly with primary amenorrha.