Complete Androgen Insensitivity Syndrome (CAIS) is a genetic disorder characterized by insensitiveness or unresponsiveness to male hormones known as androgens. Children with CAIS are born with external sex characteristics as girls but do not have a uterus, ovaries or fallopian tubes (they have short blind-pouch vagina). Despite their female appearance (gender identity is usually female), they have male internal sex organs (testes). These undeveloped tested are undescended, which means they are abnormally located in the pelvis or abdomen. Generally, the condition is discovered at puberty when the child should menstruate but menstruation does not occur. In addition to the complete androgen insensitivity syndrome there are also forms of mild androgen insensitivity in which the patient responds partially to the androgen hormones. Patients with CAIS are infertile.
Children born with this genetic disease are usually not diagnosed until puberty. There are some circumstances that may lead to a presumptive diagnosis of the syndrome. For example, some ultrasound study may reveal the presence of a small vagina, no ovaries and undescendent tested. Sometime a lump in the inguinal region may prove to be an underdeveloped male organ. A surgery for hernia, appendicitis, or any other reason may reveal lack of uterus or presence on undeveloped testes. However, in the majority of cases the condition goes undetected until puberty when a girls should menstruate but do not. Many women may ask about painful sexual intercourse and then find that they have a very small vagina or may seek counseling for infertility.
Genetics of Complete Androgen Insensitivity Syndrome
According to the Genetics Home Reference of the U.S. National Library of Medicine, the incidence of complete androgen insensitivity syndrome is 2 to 5 in 100,000 people. Partial androgen syndrome (also called partial androgen resistance syndrome) incidence is unknown.
The sex of an individual is determined by the composition of chromosome 46. Females have two of the same kind of sex chromosome (XX), while males have two distinct sex chromosomes (XY). people with CAIS are phenotypic females with a chromosomal genotype of a male (46,XY). A mutation on the X chromosome (Xq11-q12) is responsible for CIAS. The gene Xq11-q12) codes for the androgen receptor (the dihydrotestosterone receptor).
Complete androgen insensitivity syndrome is an X-linked recessive trait. Females have two X chromosomes, while males have one X and one Y chromosome. Females can be carriers (women with a single mutated copy) of the affected gene but do not necessarily express the condition (as with all the X-linked recessive conditions carriers have some symptoms of the disease). Male children of female carriers (genetically 46,XY males) will have a 50% chance of having the syndrome from carrier females.
The CAIS condition can be successfully managed. One of the issues with CAIS in the increased risk of undescendent testes to become malignant tumors during the patient life. Once the condition has been established, it is generally recommended to surgically remove testes after puberty has been reached. Gonadectomy (testes removal) is followed by estrogen replacement therapy. Also, vaginal dilatation is performed to avoid a dyspareunia (painful sexual intercourse). .
Genetics Home Reference of the U.S. National Library of Medicine (https://ghr.nlm.nih.gov/condition=androgeninsensitivitysyndrome)
Androgen Insensitivity Syndrome by Bruce Gottlieb, PhD (https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=androgen)
X-Linked recessive (carrier mother). public domain: nih.gov (https://ghr.nlm.nih.gov/handbook/illustrations/xlinkrecessivemother)