[Grouping of abnormal sexual development--guide to diagnosis]

Sexual differentiation and development is a process from the moment of fertilization of a ovum by a spermatozoon to achievement of reproductive ability as a male or female. The process includes three steps; establishment of sex chromosome composition, gonadal differentiation and development, and acquirement of phenotypic expression by gonadal hormones. Therefore, abnormal sexual development is divided into three categories according to the above three steps. In humans, however, gender is assigned at birth. Then, individuals grow under social environment provided according to the gender assigned and acquire gender role during childhood and gender identity during puberty. As observed in those with trans-sexualism, it appears likely that gender identity plays a major role on sexual behavior of humans.