Swyer Syndrome: A Look into Women with a Y-Chromosome

When we refer to our sex, what do we really mean? While it is easy to say that sex merely refers to what type of genitals we have, in reality, it is a little more complicated than that.

All humans have a pair of chromosomes. Females contain two X-chromosomes, while males have one X-chromosome and one Y-chromosome. This means that all humans have at least one X-chromosome. This chromosome is vital to the proper formation of our body. The X chromosomes also contains information relating to the formation of female-specific sex characteristics, such as the formation of a uterus, vagina, and ovaries. The Y-chromosome, on the other hand, is much smaller, and mostly contains information related to the formation of male-specific characteristics, such as the formation of male genitals. A fetus will, by default, be a female (as, barring any severe genetic disorders, it will always have at least one X-chromosome), and will only become a male if they also have a Y-chromosome. Otherwise, females will simply have an extra X-chromosome in place of a Y-chromosome. Thus, the chromosomal makeup for females will typically be XX, while the chromosomal makeup for males will be XY. Note, however, the use of the word “typically.” While genetic sex (an individual’s sex chromosomes) will typically match with their phenotypic sex (an individual’s genitalia), certain chromosomal disorders can trigger a discrepancy between the two. One such disorder is called Swyer Syndrome.

Swyer Syndrome refers to a chromosomal disorder in which a genetic male has a dysfunctional Y-chromosome. Specifically, the parts of the Y-chromosome which control the development of male genitalia are unable to function. As explained before, all fetuses will be female by default, unless a Y-chromosome is present. If the Y-chromosome is unable to actually alter the development of the fetus, however, the fetus will remain a female despite having a Y-chromosome. This fetus will thus be phenotypically female despite being genetically male, meaning that the fetus will develop female external genitalia, despite being genetically male. This alteration is not without consequence though. For one, the female will be unable to develop functioning ovaries due to only having one X-chromosome. Instead, benign tumors called gonadoblastoma will develop in place of the ovaries, rendering the female genetically sterile, and thus unable to achieve menstruation.

Another consequence is that the female will begin to experience hormonal imbalances starting at puberty, due to the presence of the Y-chromosome. While the Y-chromosome is unable to allow the formation of male genitalia, its partial functionality still reduces the overall estrogen levels of the female as she reaches puberty. If left untreated, these lower estrogen levels can prevent the female from developing certain secondary sexual characteristics. This means that females with untreated Swyer Syndrome will typically be taller than the average woman,  with smaller breasts, and an overall body type closer to that of a eunuch (a male castrated before puberty) than a of mature woman. Other negative health side effects include reduced bone mineral density, and higher risk of developing cancer due to the presence of gonadoblastoma in the body.

Swyer Syndrome can be difficult to treat, as it is symptoms don’t typically manifest until puberty, and it can only be properly diagnosed with an MRI scan. Upon identification, Swyer Syndrome is typically treated with hormone therapy throughout puberty, where additional estrogen is supplied to the patient to compensate for their own body’s lack of it. The gonadoblastoma are also typically surgically removed, so as to eliminate the cancer risk they present. With these treatments, a woman with Swyer Syndrome can avoid some of the more severe medical disorders caused by Swyer Syndrome. Furthermore, while women with Swyer Syndrome don’t have functioning ovaries, the rest of their genitalia should function normally. In fact, a woman with Swyer Syndrome can even successfully carry a fetus to term, should they opt to receive a donated ovum (though their uterus is usually smaller than those of genetic females, often necessitating a C-section). Overall, with the correct treatments, a woman with Swyer Syndrome can live a fairly normal and healthy life.


“Swyer Syndrome : Current Opinion in Endocrinology, Diabetes and Obesity.” LWW, journals.lww.com/co-endocrinology/Fulltext/2014/12000/Swyer_syndrome.13.aspx.

George Galanis