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Sex development begins in utero but continues into young adulthood with the achievement of sexual maturity and reproductive capability. The major determinants of sex development can be divided into three components: chromosomal sex, gonadal sex (sex determination), and phenotypic sex (sex differentiation) (Fig. 390-1). Variations at each of these stages can result in differences (or disorders) of sex development (DSDs) (Table 390-1). In the newborn period, ~1 in 5000 babies undergo investigation because of atypical or ambiguous genitalia. Urgent assessment is indicated, because some causes such as congenital adrenal hyperplasia (CAH) can be associated with life-threatening adrenal crises. An experienced multidisciplinary team is important for counseling, planning appropriate investigations, discussing long-term well-being, supporting parents, and providing clear communication about the diagnosis and management options. DSDs can also present at other ages and to a range of health professionals (Table 390-2). Subtler forms of gonadal dysfunction (e.g., Klinefelter syndrome [KS], Turner syndrome [TS]) often are diagnosed later in life by internists. Because DSDs are associated with a variety of psychological, reproductive, and potential medical consequences, an open dialogue must be established between the patient and health care providers to ensure continuity and attention to these issues across the life span. Gender variance and gender dysphoria are more common among some individuals with DSD than in the general population. Thus, attention to and comfort discussing gender identity is important. Support groups also have a valuable role to play for many patients and families.

FIGURE 390-1

Sex development can be divided into three major components: chromosomal sex, gonadal sex, and phenotypic sex. AMH, anti-müllerian hormone also known as Müllerian-inhibiting substance, MIS; DHT, dihydrotestosterone; T, testosterone.

TABLE 390-1Classification of Disorders of Sex Development (DSDs)a

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