XY gonadal dysgenesis
Medical condition From Wikipedia, the free encyclopedia
Medical condition From Wikipedia, the free encyclopedia
XY complete gonadal dysgenesis, also known as Swyer syndrome, is a type of defect hypogonadism in a person whose karyotype is 46,XY. Though they typically have normal vulvas,[1] the person has underdeveloped gonads, fibrous tissue termed "streak gonads", and if left untreated, will not experience puberty. The cause is a lack or inactivation of an SRY gene which is responsible for sexual differentiation. Pregnancy is sometimes possible in Swyer syndrome with assisted reproductive technology.[2][3][4] The phenotype is usually similar to Turner syndrome (45,X0) due to a lack of X inactivation. The typical medical treatment is hormone replacement therapy.[5] The syndrome was named after Gerald Swyer, an endocrinologist based in London.
| XY gonadal dysgenesis | |
|---|---|
| Other names | Swyer syndrome |
| |
| Protein SRY | |
| Specialty | Medical genetics |
Those with Swyer syndrome develop phenotypes typical of females and nonfunctional gonads. Individuals are most commonly diagnosed during adolescence after puberty fails to occur.[6]
The consequences of Swyer syndrome without treatment:
Genetic associations of Swyer syndrome include:
| Type | OMIM | Gene | Locus |
|---|---|---|---|
| 46,XY gonadal dysgenesis, complete, SRY-related | 400044 | SRY | Yp11.3 |
| 46,XY gonadal dysgenesis, complete or partial, DHH-related | 233420 | DHH | 12q13.1 |
| 46,XY gonadal dysgenesis, complete or partial, with or without adrenal failure | 612965 | NR5A1 | 9q33 |
| 46,XY gonadal dysgenesis, complete, CBX2-related | 613080 | CBX2 | 17q25 |
| 46,XY gonadal dysgenesis, complete or partial, with 9p24.3 deletion | 154230 | DMRT1/2 | 9p24.3 |
Seven other genes have been identified with probable associations that are as yet less clearly understood.[9]
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 (i.e., 45,X) and its variants, as well as those with mixed gonadal dysgenesis and a mixture 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.[10] People with PGD have a normal karyotype but may have defects of a specific gene on a chromosome.
The first known step of sexual differentiation of a male fetus is the development of testes. The early stages of testicular formation in the second month of gestation requires the action of several genes, one of the earliest and most important of which is SRY: the sex-determining region of the Y chromosome.[11][12]
When such a gene is defective, the indifferent gonads fail to differentiate into testes in an XY fetus. Without testes, no testosterone or anti-Müllerian hormone (AMH) is produced. Without testosterone, the Wolffian ducts fail to develop, so no internal male organs are formed. Also, the lack of testosterone means that no dihydrotestosterone is formed and consequently the external genitalia fail to virilize, resulting in a normal vulva.[13] Without AMH, the Müllerian ducts develop into normal internal female organs (uterus, fallopian tubes, cervix, vagina).[14]
Due to 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.[15] As 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.[16]
Evaluation of delayed puberty usually reveals elevation of gonadotropins, indicating that the pituitary is providing the signal for puberty but the gonads are failing to respond. The next steps of the evaluation usually include checking a karyotype and imaging of the pelvis.[17] The karyotype reveals XY chromosomes and the imaging demonstrates the presence of a uterus but no ovaries (the streak gonads are not usually seen by most imaging). Although an XY karyotype can also indicate a person with complete androgen insensitivity syndrome, the absence of breasts, and the presence of a uterus and pubic hair exclude the possibility. At this point it is usually possible for a physician to make a diagnosis of Swyer syndrome.[18]
Swyer syndrome represents one phenotypic result of a failure of the gonads to develop properly, and hence is part of a class of conditions termed gonadal dysgenesis. There are many forms of gonadal dysgenesis.[19]
Swyer syndrome is an example of a condition in which an externally unambiguous female body carries dysgenetic, atypical, or abnormal gonads.[20] Other examples include complete androgen insensitivity syndrome, partial X chromosome deletions, lipoid congenital adrenal hyperplasia, and Turner syndrome.[21]
Upon diagnosis, estrogen and progestogen therapy is typically commenced, promoting the development of female characteristics.
Hormone replacement therapy can also reduce the likelihood of osteoporosis.[1]
A 2017 study estimated that the incidence of Swyer syndrome is approximately 1 in 100,000 females.[22] Fewer than 100 cases have been reported as of 2018. There are extremely rare instances of familial Swyer syndrome.[23][24]
Swyer syndrome was first described by G. I. M. Swyer in 1955 in a report of two cases.[23]
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