TABLE I.

Conditions in Which Variations in Hormone Exposure or Sensitivity Allow for Assessment of the Biological Contribution to Sexual Differentiation of the Human Brain

Condition	Hormonal impact	Effects on sexual differentiation of the brain
DES exposure in utero	Elevated estradiol during brain development	Inconsistent or modest effects on masculinization or feminization
Estrogen insensitivity	Exceedingly rare but recently discovered men with mutations in the aromatase gene or estrogen receptor	Mild reduction in libido but otherwise normal
Androgen insensitivity syndrome	Spontaneous mutation of the androgen receptor gene results in complete or partial loss of cellular sensitivity to androgens	XY males develop as behaviorally phenotypic females
5-Alpha reductase deficiency	Reduced production of DHT leads to incomplete masculinization of genitalia at birth, masculinization proceeds at puberty	Majority of XY individuals choose to live as males post puberty
Congenital Adrenal hyperplasia (CAH)	Elevated androgen exposure in utero, girls born with partially masculinized genitalia	Small but significant increase in homosexuality, significant shift towards male-typic behaviors but within the normal range
Klinefelter syndrome (XXY)	Reduced androgen exposure in males throughout life	Behavioral changes and significant deficits in speech and language capabilities