Disorders of sexual differentiation are individually rare but in aggregate not uncommon. In this chapter we consider those disorders most likely to occur in adolescent females or infants with genital ambiguity. This chapter reflects a number of research contributions. 1,2 Primordial germ cells originate in the endoderm of the yolk sac and migrate to the genital ridge to form the indifferent gonad, which is initially indistinguishable in 46,XY and 46,XX embryos. Indifferent gonads develop into testes if the embryo – or more specifically the gonadal stroma – is 46,XY. This process begins about 43 days after conception. Testes become morphologically identifiable 7-8 weeks after conception (9-10 gestational or menstrual weeks).
