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.
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.
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)