Disorders of Sex Development

Introduction Sexual differentiation is the process of development of the differences between male and female from an undifferentiated zygote (fertilised egg). Sex and gender are both important determinants of health. The term “gender” describes those characteristics of females and males that are largely socially created, whereas “sex” encompasses those characteristics that are biologically determined. Disorders of sex development (DSDs) have been endorsed by the Chicago Consensus to replace the term “intersex”. The proposed changes in terminology are summarised in Table 99.1. DSD is defined as a congenital condition in which development of chromosomal, gonadal, or anatomical sex is atypical. Approximately 1 in 2,000 children globally is born with a DSD condition. This term uses chromosomes, rather than gonads, as the most important classifier of an individual’s sex. In some DSDs, there is an associated obvious genital ambiguity at birth, whereas in others, the external genitalia are typically male or typically female, but the internal anatomy is discordant. Associated endocrinal and other congenital anomalies are always present. Demographics DSDs occur more commonly in developing countries. Certain areas of the world have a high incidence for certain genetic forms of DSD (see section on “Aetiology and Classification” for a discussion of gene deficiencies). 5α-reductase deficiency was first reported on one island in the Dominican Republic. It is also prevalent in southern Lebanon and the Eastern Highlands Province of Papua New Guinea, but is relatively rare in caucasians. 17β-Hydroxysteroid dehydrogenase deficiency is very common in the Gaza Strip. Both of these conditions can lead to a gradual transition in gender identity from female to male. In southern African blacks, 46,XX ovotesticular DSD has an unusually high prevalence.