An inherited disorder caused by androgen insensitivity with affected males having a normal male (46,XY) karyotype, but female phenotype with normal female external genitalia and abnormal or absent internal female organs. The testes are often intraabdominal, inguinal, or labial.
Testicular Feminization; Androgen Receptor Deficiency; Dihydrotestosterone Receptor Deficiency; Male Pseudohermaphroditism as a Result of Androgen Insensitivity; Hairless Women Syndrome.
Estimates vary 1-5:100,000 live births. No racial predilection has been reported.
X-linked recessive with the responsible gene encoding for the androgen receptor being located on Xq12. More than 200 different mutations have been described.
The basic etiology of androgen insensitivity syndrome (AIS) is a mutation in the androgen receptor gene that results in the gene’s loss of function. The functional defects can range from complete absence of receptors on the cell surface to decreased substrate binding affinity with loss of signal transmission. Despite normal or elevated levels of androgen, functional loss of the androgen receptor is clinically equivalent to a lack of androgen and results in prenatal undervirilization of external genitalia, and absence of pubic and axillary hair, lack of acne, and absence of voice changes in puberty. Leydig cell stimulation to estrogen production occurs probably due to a failure in feedback repression of the pituitary gland, which shares the unresponsiveness to androgen. Peripheral conversion of testosterone and androstenedione to estradiol finally results in elevated estrogen serum levels. This on the one hand explains the absence of (androgen mediated) axillary and pubic hair, acne, and voice changes and on the other hand the development of normal breasts in these patients.
The clinical findings of inguinal hernia with a labial mass in infancy and primary amenorrhea despite typical female secondary sex characteristics, but scant or absent pubic and axillary hair in puberty should raise suspicion for AIS. Affected males have female external genitalia associated with normal or high testosterone serum levels. In infancy, plasma luteinizing hormone (LH) and testosterone levels and the response to luteinizing hormone-releasing hormone (LHRH) are higher than in age-matched controls. In puberty, the androgen insensitivity, which also affects the hypothalamic-pituitary area, results in elevated testicular androgen and estradiol synthesis.
These genotypic male patients are phenotypic females. Anatomically, they have normal female external genitalia but a blind-ending vaginal pouch and absent uterus and fallopian tubes. The testes usually are located intraabdominally, in the inguinal canal, or in the labia. Leydig cells appear hyperplastic and form adenomatous clumps. Primary amenorrhea and scant pubic and axillary hair contrast with well-developed female personality and body shape (including breasts). The patients often appear tall for females, and the clinical signs result from high estrogen levels. Other features ...