Now more appropriately called the complete androgen insensitivity syndrome, this is a genetic disorder that makes XY fetuses insensitive (unresponsive) to androgens (male hormones). Instead, they are born looking externally like normal girls. Internally, there is a short blind-pouch vagina and no uterus, fallopian tubes or ovaries. There are testes in the abdomen or the inguinal canal.
The complete androgen insensitivity syndrome is usually detected at puberty when a girl should but does not begin to menstruate. Many of the girls with the syndrome have no pubic or axillary (armpit) hair. They have luxuriant scalp hair without temporal (male-pattern) balding. They are sterile and cannot bear children. They are at high risk for osteoporosis and so should take estrogen replacement therapy.
The gene for the syndrome is on the X chromosome in band Xq11-q12. The gene codes for the androgen receptor (also called the dihydrotestosterone receptor). This gene is mutant in the complete androgen insensitivity syndrome. Because of the mutation, the cells cannot respond to androgen. If a woman has the mutation on one of her X chromosomes, the risk for each of her XY offspring to receive the gene and have the syndrome is one-half (50%).
There are also partial androgen insensitivity syndromes. They usually result in micropenis with hypospadias and gynecomastia (male breast development). These conditions (which include a disorder called Reifenstein syndrome) are also due to mutations in the androgen receptor gene.
The complete androgen insensitivity syndrome was once referred to as testicular feminization (TFM). The name “complete androgen insensitivity syndrome” is scientifically accurate and is more satisfactory to patients and their families.
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