SRY Gene

Swyer syndrome is a condition that affects sex development. Sex development usually follows a particular path based on an individual's chromosomes; however, in Swyer syndrome, sex development is not typical for the affected individual's chromosomal pattern.

People usually have 46 chromosomes in each cell. Two of the 46 chromosomes, known as X and Y, are called sex chromosomes because they help determine whether a person will develop male or female sex characteristics. Girls and women typically have two X chromosomes (46,XX karyotype), while boys and men typically have one X chromosome and one Y chromosome (46,XY karyotype). In Swyer syndrome, individuals have one X chromosome and one Y chromosome in each cell, which is the pattern typically found in boys and men; however, they have female reproductive structures.

People with Swyer syndrome have female external genitalia and some female internal genitalia;  the uterus and fallopian tubes are normally-formed, but the gonads (ovaries or testes) are not functional. Instead, the gonads are small and underdeveloped and contain little gonadal tissue. These structures are called  streak gonads. The streak gonadal tissue is at risk of developing hard-to-detect cancers, so it is usually removed surgically. Swyer syndrome is sometimes called 46,XY complete gonadal dysgenesis; the medical term “dysgenesis” indicates that development (in this condition, development of the gonads) is reduced and not typical.

People with Swyer syndrome are usually raised as girls and have a female gender identity. Swyer syndrome may be identified before birth, at birth, or later when a child does not go through puberty as usual. Because they do not have functional ovaries that produce hormones, affected individuals often begin hormone replacement therapy during adolescence to start puberty, causing the breasts and uterus to grow, and eventually leading to menstruation. Hormone replacement therapy also stimulates bone development and helps reduce the risk of abnormally low bone density (osteopenia and osteoporosis). Women with Swyer syndrome do not produce eggs (ova), but they may be able to become pregnant with a donated egg or embryo.