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.\n\nChromosomes contain the genetic instructions for how the body develops and functions. 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 reproductive structures. 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.\n\nBecause they appear female on the outside, babies with Swyer syndrome are usually raised as girls and develop a female gender identity, which is a person's sense of their gender (girl, boy, a combination, or neither). 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 early adolescence to start puberty, causing the breasts and uterus to grow, and eventually leading to menstruation. Hormone replacement therapy is also important for bone health and helps reduce the risk of low bone density (osteopenia) and fragile bones (osteoporosis). Women with Swyer syndrome do not produce eggs (ova), but if they have a uterus, they may be able to become pregnant with a donated egg or embryo.\n\nPeople with Swyer syndrome have female external genitalia and some female internal reproductive structures. These individuals usually have a uterus and fallopian tubes, but their 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 cancer that is often hard-to-detect, so it is usually removed surgically. Swyer syndrome is also called 46,XY complete gonadal dysgenesis; the medical term “dysgenesis” means "abnormal development." [from MedlinePlus Genetics]
