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Swyer syndrome, or XY gonadal dysgenesis, is a type of hypogonadism in which no functional gonads are present to induce puberty in an externally female person whose karyotype is then found to be XY. The gonads are found to be nonfunctional streaks. Estrogen and progesterone therapy is usually then commenced. The gonads are normally removed surgically because they do not function and may develop cancer.
There are several forms of gonadal dysgenesis. The term “pure gonadal dysgenesis” (PGD) has been used to describe conditions with normal sets of sex chromosomes (e.g., 46,XX or 46,XY), as opposed to those whose gonadal dysgenesis results from missing all or part of the second sex chromosome. The latter group includes those with Turner syndrome (e.g., 45,X) and its variants, as well as those with mixed gonadal dysgenesis and a mixtures of cell lines, some containing a Y chromosome (e.g., 46,XY/45,X).
Thus Swyer syndrome is referred to as PGD, 46,XY, and XX gonadal dysgenesis as PGD, 46,XX.[1] Patients with PGD have a normal chromosomal constellation but may have defects of a specific gene on a chromosome.
The first known step of sexual differentiation of a normal XY fetus is the development of testes. The early stages of testicular formation in the second month of gestation require the action of several genes, of which one of the earliest and most important is SRY, the “sex-determining region of the Y chromosome”. Mutations of SRY account for many cases of Swyer syndrome.
When such a gene is defective, the indifferent gonads fail to differentiate into testes, in an XY (genetically male) fetus. Without testes, no testosterone or antimullerian hormone (AMH) are produced. Without testosterone the external genitalia fail to virilize, resulting in normal female genitalia, and the wolffian ducts fail to develop, so no internal male organs are formed. Without AMH, the mullerian ducts develop into normal internal female organs (uterus, fallopian tubes, cervix, vagina).
A baby who is externally a girl is born and is normal in all anatomic respects except that she has nonfunctional streak gonads instead of ovaries or testes. As girls’ ovaries normally produce no important body changes before puberty, a defect of the reproductive system typically remains unsuspected in girls with Swyer syndrome until puberty fails to occur.
Because of the inability of the streak gonads to produce sex hormones (both estrogens and androgens), most of the secondary sex characteristics do not develop. This is especially true of estrogenic changes such as breast development, widening of the pelvis and hips, and menstrual periods. Because the adrenal glands can make limited amounts of androgens and are not affected by this syndrome, most of these persons will develop pubic hair, though it often remains sparse.
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