The genetics of disorders of sex development in humans

One of the defining events during human embryonic development with the most far-reaching effects for the individual is whether the embryo develops as male or female. The crucial step in this process is the differentiation of the bipotential embryonic gonads into either testes or ovaries. If the embryo inherits X and Y sex chromosomes, the Y-linked SRY (sex determining region in Y) gene initiates a network of genes that results in a functional testis and ultimately a male phenotype. By contrast, in an embryo with 2 X chromosomes, the undifferentiated gonad develops as an ovary resulting in a female phenotype. Perturbation of any of the genes in either the testicular or ovarian developmental pathway can result in individuals with disorders of sex development. In this review, we provide a summary of known components of testicular or ovarian pathways and their antagonistic actions and give a brief overview of new technologies currently used to identify the missing pieces of the sex development network.