Disorders of Sex Development
When a child's gender is in question at birth, because the genitals may not appear clearly male or female, the child is said to have atypical genitalia, also known as ambiguous genitalia. Atypical genitalia can be a difficult experience for families.
What are disorders of sex development (DSD)?
Early in fetal development, the tissue that will become the gonads (ovaries or testes) is undifferentiated and has the potential to become either ovaries or testes, depending on the genetics of the fetus. Humans have 46 chromosomes in each cell of their bodies, or 23 pairs. The 23rd pair determines our gender; females have two X chromosomes, while males have one X and one Y chromosome. The description of human chromosomes is written: 46, XX, typical female or 46, XY, typical male.
There is a gene located on the short arm (top half) of the Y chromosome, called "SRY," which, if present, will cause the undifferentiated gonad to become testes (indicating a male) around the 6th week of fetal life. At the same time, regression of what would have been the female reproductive tract occurs. As the testes produce testosterone, the phallus (penis), scrotum, and urethra form. Later, during the 7th to 8th month of the pregnancy, the testes will descend into the scrotum.
In the absence of the SRY gene, the gonad will differentiate into an ovary (indicating a female). Likewise, the female reproductive tract will continue to develop, forming the uterus and fallopian tubes. At the same time, regression of what would have become the male reproductive organs occurs.
Besides the SRY gene, certain hormones can influence the development of the sexual organs. These hormones are secreted during the early weeks of gestation and include the anti-Müllerian hormone, testosterone hormone, and dihydrotestosterone, an active derivative of testosterone.
A variety of genetic and environmental factors may influence this development, leading to atypical genitalia. Ambiguous genitalia, as the term implies, may make determining the child's gender more difficult. Very few infants with atypical genitalia have genitals that are so ambiguous that a gender determination is not made at birth. Far more common are the following observations at birth:
A female with severe virilization (overproduction of male hormones) who appears to have a small penis
A male with an abnormally small penis that resembles a female clitoris (due to an insensitivity to male hormones or failure to produce male hormones)