Urology :: Understanding Disorders of Sex Differentiation
Disorders of sex differentiation, also known as disorders of sexual development or DSD, are conditions in which the sexual development that occurs during fetal growth does not happen as it should. DSD can develop genetically, be inherited or have no identifiable cause. The most common disorders in newborns are congenital adrenal hyperplasia and mixed gonadal dysgenesis.
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 chromosomes are referenced as 46, XX, for a normal female or 46, XY, for a normal male.
During fetal development the tissue that eventually becomes the gonads (ovaries or testes) receives signals based on the child’s genetics. There is a gene located on the top portion of the Y chromosome, called "SRY," which, if present, will cause the gonad to become testes (indicating a male) around the sixth week of fetal life. This will also cause the regression of what would have been in the female reproductive tract. As the testes grow and start to produce testosterone, the penis, scrotum and urethra form.
In the absence of the “SRY” gene, the gonad will turn into an ovary (indicating a female). The female reproductive tract will continue to develop, forming the uterus and fallopian tubes. At the same time, what would have become the male reproductive organs goes away.
Besides the SRY gene, certain hormones can influence the development of the sexual organs. These hormones are secreted during the early weeks of pregnancy and include the anti-Müllerian hormone, testosterone hormone, and dihydrotestosterone, an active derivative of testosterone.
Children with DSD will normally have atypical-appearing genitalia (genitalia that do not look normal) at birth. Atypical genitalia may make determining the child’s sex more difficult. Children are quickly referred to one of our specialists for in depth analysis to determine the underlying disorder. Although most children with DSD will have atypical appearing genitalia not all children will. The appearance and severity of DSD varies greatly in each child.