Variations of Sex Characteristics/Differences of Sex Development
The development of any person's sex characteristics is the result of a complex interaction between chromosomes (structures composed of DNA and proteins contained in each cell) and hormones (molecules –proteins or steroids– produced by endocrine glands and released into the bloodstream). In humans, the genetic information contained in each cell is divided into 46 chromosomes (23 pairs). The twenty-third pair determines our chromosomal sex; females usually have two X chromosomes (46,XX), while males usually have one X chromosome and one Y chromosome (46,XY).
At the beginning of fetal development, the tissue that will give rise to the gonads (testes or ovaries) is undifferentiated: it can develop in either direction. If there is a gene located on the Y chromosome, the so-called “SRY” gene, the undifferentiated gonad will become a testis. While the testes are producing testosterone, the typical male internal and external genitalia are formed. Later on, during the seventh to eighth month of pregnancy, the testes slide down into the scrotum. Without the SRY gene, the gonad will differentiate into ovaries, and the typically female anatomical structures will form.
Various genetic, hormonal and environmental factors can influence this process and cause variations referred to as “Variations of Sex Characteristic” (VSCs) or "Differences of Sex Development" (DSDs), which will be described one by one.
