Normal Sexual Development

Sexual differentiation in humans is controlled by genetics (presence of Y chromosome determines development of testis and absence determines development of ovary with additional X chromosome), environment (e.g., nutrition), and hormones (MacLaughlin and Donahoe, 2004). Congenital conditions associated with aberrations of chromosomal, gonadal, or anatomic sexual development are called "disorders of sex development (DSD)" (Houk et al., 2006). In the postgonadal phase, hormones control external genitalia differentiation and secondary sexual development. Puberty refers to a physiologic transition phase (>4 years) between childhood and adulthood during which there is pubertal growth spurt and development of secondary sexual characteristics. Puberty is preceded by adrenarche (6-7 years in females and 7-8 years in males), marked by increasing amounts of adrenal androgens (DHEA, DHEA-S, and androstenedione). The growth spurt (striking increase in growth velocity during puberty) is a complex hormonal phenomenon in which GH, thyroid hormones, and sex steroids play a major role. Gonadarche (secretion of gonadal sex steroids) follows adrenarche and is initiated by activation of the GnRH pulse generator in the hypothalamus. These GnRH pulses result in increased gonadotropin secretion and subsequent production of sex hormones by the gonads.

Sexual maturation in females starts with breast development (thelarche) at a mean age of 11 years, followed by pubic hair development and menses (menarche). In males it starts with scrotal corrugation and testicular enlargement at a mean age of 11.5 years, followed by growth of the penis and pubic hair.

In males, release of LH stimulates testicular Leydig cells to produce testosterone. FSH, in conjunction with testosterone, stimulates spermatogenesis. In females, FSH stimulates development of primary ovarian follicles and increases production of estrogen from ovarian granulosa cells. LH in females stimulates ovarian theca cells to produce andro-gens and the corpus luteum to synthesize progesterone. LH induces ovulation through the midcycle surge.

Estradiol production in males increases the bone age, bone mineral density, and rate of epiphyseal fusion. In females it stimulates the development of breasts, labia, vagina, and uterus and proliferation of endometrium. In addition, estra-diol enhances development of, and increase in, the ducts of the breast and body fat. Estrogen in low levels enhances linear growth, and high levels increase the rate of fusion of epiphy-ses. Testosterone is responsible for the increase in muscle mass, sebaceous glands, and voice changes seen in pubertal males and is a linear growth accelerator. In females, testosterone accelerates linear growth and stimulates pubic and axillary hair development. Progesterone in females is responsible for development of a secretory endometrium and plays a role in breast development. Linear growth and pubic hair development in both males and females are caused by androgens from the adrenal gland. Figures 35-5 and 35-6 show normal pubertal developmental stages of Marshall and Tanner.

• Evaluation should begin if signs of puberty develop in girls younger than 8 years or boys younger than 9 years.

• Diagnoses of true puberty and pseudopuberty should be differentiated.

• Evaluation includes a comprehensive history and physical examination, growth chart, and wrist radiograph.

• If true puberty is suspected, consider cranial CT or MRI to rule out CNS lesions.

Evaluation of suspected abnormal puberty begins with obtaining a detailed history, including growth and development (timing of physical and developmental milestones), medical conditions, dietary history, social history, ethnicity, and family history. Physical examination should be thorough, including current weight and a focus on development of secondary sexual characteristics and genitalia. A detailed growth chart from birth to present day should be obtained. A radiograph of the left wrist is needed to estimate bone age (Blondell et al., 1999).

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